tag:theconversation.com,2011:/us/topics/snow-1407/articlesSnow – The Conversation2024-03-13T19:15:13Ztag:theconversation.com,2011:article/2255812024-03-13T19:15:13Z2024-03-13T19:15:13ZTennis anyone? Bad news for skiers as snow season could shrink by 78% this century<p>As the days shorten, many of us, particularly in Australia’s south-east, are looking forward to cooler times, and perhaps the allure of snow on the horizon. In the past week many in this region experienced their <a href="https://www.theguardian.com/australia-news/2024/mar/10/hobart-endures-hottest-night-in-112-years-as-severe-heatwave-hits-south-eastern-australia">warmest days for over a century</a>. What does this bode for times to come?</p>
<p><a href="https://doi.org/10.1371/journal.pone.0299735">Research</a> released overnight suggests ski areas in Australia and Aotearoa New Zealand will soon have much less snow due to climate change. German researcher Veronika Mitterwallner and her colleagues show average annual snow-cover days may decline by 78% in the Australian Alps and 51% in the Southern Alps of Aotearoa New Zealand (under a high-emissions scenario) by 2071–2100. Worldwide, they found 13% of ski areas will lose all natural snow cover by the end of the century. </p>
<p>It’s <a href="https://www.facebook.com/photo.php?fbid=617796527113271&set=pb.100066487878368.-2207520000&type=3&paipv=0&eav=AfaxRFHwY-3bvBmVsaq89GJJD_KbCitxFy9ExZef_YY5iwR1SbFy80eVARtIAgSDcuI&_rdr">often said</a> Australia gets more snow than Switzerland, though the evidence <a href="https://business.weatherzone.com.au/news/does-australia-really-have-more-snow-than-switzerland/">says otherwise</a>. The fact remains that the Australian Alps cover a large area, more than 12,000km, with a <a href="https://www.int-res.com/articles/cr2016/68/c068p025.pdf">third or more</a> covered in snow at peak times. So these changes will have a broad impact on local economies and threaten fragile alpine ecosystems.</p>
<figure class="align-center ">
<img alt="a panoramic view of the Australian Alps covered in snow" src="https://images.theconversation.com/files/581462/original/file-20240313-20-3ydx39.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581462/original/file-20240313-20-3ydx39.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=243&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581462/original/file-20240313-20-3ydx39.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=243&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581462/original/file-20240313-20-3ydx39.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=243&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581462/original/file-20240313-20-3ydx39.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=306&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581462/original/file-20240313-20-3ydx39.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=306&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581462/original/file-20240313-20-3ydx39.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=306&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">If Australia loses three-quarters of its snow-cover days, a surprisingly big area will be affected.</span>
<span class="attribution"><span class="source">Greg Brave/Shutterstock</span></span>
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</figure>
<h2>How did the study make these findings?</h2>
<p>Mitterwallner’s team used a high-resolution climate data set for the global land surface area to identify the annual number of natural snow-cover days. Then, they projected those data under three emissions scenarios, and looked at historical (1950-2010), present (2011-2040), immediate future (2041-2070) and near future (2071-2100) data to examine changes over time.</p>
<p>Under most modelled emission scenarios, they found the annual number of snow-cover days will greatly decrease worldwide. For Australia and Aotearoa New Zealand, in particular, they found the average number will decrease by 78% and 51% respectively. These were the two regions with the greatest losses of snow.</p>
<p>However, under a low-emissions scenario, the good news is no regions will fall below an average of 100 snow-cover days a year. This is historically the minimum number of days a ski resort needs in seven out of ten winters <a href="https://link.springer.com/article/10.1007/s00484-020-01867-3#">to remain viable</a> (cover must be at least 30–50cm).</p>
<h2>How will we adapt to the loss of snow?</h2>
<p>Will the way we use our alpine areas have to change permanently? Many resorts have already pivoted to activities such as mountain biking that don’t rely on snow. Skiing may be off the agenda – tennis anyone?</p>
<p>The prognosis of such research has driven the formation of groups such as <a href="https://protectourwinters.org/about-pow/">Protect Our Winters</a>. The mission of the <a href="https://protectourwinters.org.au">Australian section</a> is to help Australia’s outdoor community protect the integrity of our unique alpine environment and lifestyle from climate change.</p>
<p>Beyond Australia, New York recently had its <a href="https://abcnews.go.com/US/live-updates/snowstorm-northeast-nyc/snow-totals-near-new-york-city-107198753?id=107160643">highest snowfall in two years</a>. Across the United States in general, though, they just experienced the <a href="https://edition.cnn.com/2024/03/08/weather/winter-warmth-record-climate/index.html">warmest winter ever</a>.</p>
<p>What is going on? And what might this new research mean, particularly for Australia and Aotearoa New Zealand?</p>
<p>These predictions, for almost all emissions scenarios, do not bode well for the skiers among us. More importantly, as many <a href="https://www.sciencedirect.com/science/article/pii/S2468312421000183#ab010">communities in the Himalaya</a> are finding out, snow is not just a recreational “nice to have”. It’s a life-source for alpine communities, both human and non-human, and all those that depend on rivers sustained by snow melt around the globe.</p>
<p>Perhaps a greater concern in our region is the potential for ecological damage as resorts seek to increase ski slope metreage in areas that remain snow-covered. Expanding resort footprints is not a sustainable approach to a problem that probably won’t be going away. </p>
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<img alt="A snow machine shoots out a plume of snow in the Snowy Mountains" src="https://images.theconversation.com/files/581468/original/file-20240313-16-f1zu2a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/581468/original/file-20240313-16-f1zu2a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=364&fit=crop&dpr=1 600w, https://images.theconversation.com/files/581468/original/file-20240313-16-f1zu2a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=364&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/581468/original/file-20240313-16-f1zu2a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=364&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/581468/original/file-20240313-16-f1zu2a.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=457&fit=crop&dpr=1 754w, https://images.theconversation.com/files/581468/original/file-20240313-16-f1zu2a.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=457&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/581468/original/file-20240313-16-f1zu2a.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=457&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Resorts can make artificial snow, but that doesn’t solve the problem of it melting if the alps get warmer.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/snow-machine-sunset-snowy-mountians-background-2321559725">Edward Atkin/Shutterstock</a></span>
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</figure>
<h2>Is artificial snow an option?</h2>
<p>So how might we support the goals of Protect Our Winters? What alternatives do we have? How about artificial snow, would that work?</p>
<p>As part of my PhD studies many years ago, at the University of Cambridge’s Scott Polar Research Institute, I made masses of “polar snow” in a cold room (while effectively destroying the air-conditioning units at the same time). Artificial snow can be created quite readily, assuming enough water is at hand. </p>
<p>Artificial snow will have a different form and its density and microstructure will differ, potentially affecting longevity. (You can read more about snow mechanics <a href="https://blogs.egu.eu/divisions/cr/2022/06/10/what-is-snow-mechanics-and-why-should-we-care/">here</a>.) </p>
<p>But once on the ground, artificial snow, like natural snow, is subject to the vagaries of our weather. If the sun is shining and the day is hot, snow won’t last long, regardless of whether it’s natural or artificial.</p>
<p>There’s a lot to think on here as we contemplate what our world and our region might look like when skiing and snow-covered ground become no more than a memory in some areas. Yes, our recreational activities might change as we wonder whether it’s worth waxing up the skis this year – or is it time to break out the racquets? The ongoing survival of many communities might be jeopardised as a result.</p><img src="https://counter.theconversation.com/content/225581/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adrian McCallum does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The two alpine regions projected to suffer the greatest loss of snow cover in the world are in Australia and Aotearoa New Zealand.Adrian McCallum, Discipline Lead - Engineering, University of the Sunshine CoastLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2231532024-03-04T18:25:48Z2024-03-04T18:25:48ZGlobal warming may be behind an increase in the frequency and intensity of cold spells<figure><img src="https://images.theconversation.com/files/575431/original/file-20240213-30-h2gkre.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5991%2C3988&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/bradford-uk-02-08-2024-electronic-2423109221">bennphoto / Shutterstock</a></span></figcaption></figure><p>Global warming caused by increased concentrations of greenhouse gases is already affecting our lives. Scorching summers, more intense heatwaves, longer drought periods, more extended floods, and wilder wildfires are consequences linked to this warming.</p>
<p>One less obvious consequence of global warming is also getting growing attention from scientists: <a href="https://www.scientificamerican.com/article/extreme-cold-snaps-could-get-worse-as-climate-warms/#:%7E:text=Many%20studies%20have%20shown%20that,and%20understood%20from%20physical%20reasoning.">a potential increase</a> in the intensity and frequency of winter cold snaps in the northern hemisphere.</p>
<p>Weather phenomena like the <a href="https://www.theguardian.com/uk-news/2018/feb/26/uk-braces-for-beast-from-the-east-as-met-office-warns-of-snow">Beast from the East in winter 2018</a>, the <a href="https://www.ncei.noaa.gov/news/great-texas-freeze-february-2021">cold spell of Arctic air</a> that reached as <a href="https://www.texastribune.org/2022/02/17/texas-winter-storm-2021-stories/">far South as Texas in February 2021</a>, or the storm that left <a href="https://www.nytimes.com/2021/01/11/world/europe/spain-snow-storm-filomena.html">Madrid</a> and <a href="https://www.theguardian.com/artanddesign/gallery/2021/feb/16/unusually-heavy-snow-blankets-athens-in-pictures">Athens</a> unusually covered in snow for days in early 2021 are becoming more common.</p>
<p>Some of the mechanisms that lead to their occurrence are strengthened by global warming. Key climate mechanisms, like exchanges of energy and air masses between different altitude ranges in the atmosphere, are evolving in ways expected to cause an increase in both the intensity and duration of cold snaps. These link to the behaviour of a region in the high atmosphere called the stratosphere.</p>
<p>Winter cold snaps have major societal impacts, from direct effects on health and loss of life, to effects on transport and infrastructure, surges in energy demand and damage to agricultural resources. </p>
<figure class="align-center ">
<img alt="Acropolis in 2021." src="https://images.theconversation.com/files/577870/original/file-20240226-21-zie9ae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/577870/original/file-20240226-21-zie9ae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/577870/original/file-20240226-21-zie9ae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/577870/original/file-20240226-21-zie9ae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/577870/original/file-20240226-21-zie9ae.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/577870/original/file-20240226-21-zie9ae.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/577870/original/file-20240226-21-zie9ae.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The Acropolis in Athens covered in snow in 2021.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/athens-greece-february-16-2021-acropolis-2258307795">Savvas Karmaniolas / Shutterstock</a></span>
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<p>This winter, we have seen these effects over large parts of Europe and the US, with flight cancellations, airport closures, road queues and drivers trapped in extreme cold temperatures. There have also been sharp increases in energy demand to cope with indoor heating, an increase in cold-related hospital admissions and the activation of services needed to assist the most vulnerable.</p>
<p>We need to develop forecasting tools that can predict these events further in advance.</p>
<h2>Polar vortex</h2>
<p>Some of these cold snaps are linked to disruptions in a seasonal atmospheric phenomenon called the stratospheric polar vortex (SPV). </p>
<p>In the northern hemisphere, this vortex consists of masses of cold air centred over the north pole, surrounded by a jet of very strong westerly winds between 15-50km above ground. These spinning winds act as a wall and keep cold air confined to the Arctic region, stopping it from travelling to lower latitudes. </p>
<p>Something that can disrupt the vortex is a sudden stratospheric warming (SSW), when the stratosphere experiences an abrupt increase in temperature due to energy and momentum being transferred from lower to higher altitudes. </p>
<p>When a major SSW occurs, the wall of strong winds around the polar stratosphere can break, allowing cold air to escape the polar vortex and travel down to lower atmospheric altitudes and lower latitudes. When that air approaches the Earth’s surface, significant cold spells can occur.</p>
<p>Even when SSWs are not strong enough to break the vortex, they can weaken it. This can cause polar air circulation patterns to meander further south into lower latitudes, reaching populated areas of North America and Eurasia, instead of staying nearer the north pole. Those areas can then experience temperatures tens of degrees lower than their winter average.</p>
<p>Under climate change, the transfer of energy from the lowest layers of the Earth’s atmosphere to the higher stratospheric layer is changing and seems to be disrupting the polar vortex to a greater degree. A <a href="https://acp.copernicus.org/articles/23/1259/2023/">study has shown</a> that the strength and duration of SSWs in the stratosphere have increased over the last 40 years. This increase is also expected to result in stronger winter cold snaps at surface levels.</p>
<figure class="align-center ">
<img alt="Polar Vortex" src="https://images.theconversation.com/files/579217/original/file-20240301-22-1lzoqr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/579217/original/file-20240301-22-1lzoqr.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=359&fit=crop&dpr=1 600w, https://images.theconversation.com/files/579217/original/file-20240301-22-1lzoqr.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=359&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/579217/original/file-20240301-22-1lzoqr.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=359&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/579217/original/file-20240301-22-1lzoqr.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=451&fit=crop&dpr=1 754w, https://images.theconversation.com/files/579217/original/file-20240301-22-1lzoqr.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=451&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/579217/original/file-20240301-22-1lzoqr.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=451&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption">The polar vortex is a crucial component in cold snaps affecting the Northern Hemisphere.</span>
<span class="attribution"><a class="source" href="https://ozonewatch.gsfc.nasa.gov/facts/vortex_NH.html">NASA</a></span>
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<h2>Forecasting challenge</h2>
<p>Accurately forecasting these cold snaps is crucial for helping society prepare appropriately for them. Developing computer-based forecasting tools that reproduce realistic interactions between the lower levels of the troposphere and the stratospheric region is an essential step towards this goal.</p>
<p>To correctly simulate the behaviour of the stratosphere and how it interacts with the troposphere, forecasting tools must include realistic descriptions of the abundance and distribution of stratospheric ozone. Ozone influences the interaction of air masses outside and inside the vortex, and therefore also the transport of colder air from higher to lower altitudes.</p>
<p>However, including all the chemical processes that ozone is involved in, at the resolution needed to predict these weather events, is prohibitive in terms of the computing power needed. This is even truer if we want to predict events one season ahead. </p>
<p>My research looks at ways to improve forecasting models to better capture the type of stratospheric behaviour that leads to these cold spells. To do this I have developed alternatives that can realistically simulate processes in the stratosphere, including aspects of ozone chemistry, using less computing power. </p>
<p>In a <a href="https://acp.copernicus.org/articles/22/4277/2022/">study I led</a>, we used these alternatives to simulate interactions between the ozone layer, temperature and solar radiation in the global computer model used to produce some of the best weather forecasts in the world.</p>
<p>The experiments we did with this model showed that including this realistic alternative representation of stratospheric ozone led to improvements in simulations of temperature distribution in the stratosphere. This means that it can help provide useful information about triggers of cold spells like SSWs.</p>
<p>Developing and using these alternatives in climate modelling is a significant milestone towards what we call seamless prediction: using the same computer modelling tools to predict both weather and climate. This allows for a more accurate establishment of causal links between climate change and extreme weather events.</p>
<p>A question many may be wondering is if this extreme cold could be counteracting global warming. Unfortunately, not. While this winter has brought days of extremely cold temperatures and heavy snowfall in the northern hemisphere, the current summer in the southern hemisphere has seen some of the hottest days on record for populated areas of Australia, with temperatures of around 50ºC.</p>
<p>Global warming makes extreme weather more extreme, and scientific studies are starting to provide proof that this also applies to extreme winter cold spells. Developing the best possible modelling tools is essential to predict the evolution of extreme weather events in the coming years so that we can be better prepared for them.</p>
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<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p class="fine-print"><em><span>Beatriz Monge-Sanz does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Cold snaps can affect everyday services and infrastructure, putting lives at risk.Beatriz Monge-Sanz, Senior Researcher, Department of Physics, University of OxfordLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2228512024-02-26T13:38:23Z2024-02-26T13:38:23ZHow is snow made? An atmospheric scientist describes the journey of frozen ice crystals from clouds to the ground<figure><img src="https://images.theconversation.com/files/576863/original/file-20240220-22-v6kq2o.jpg?ixlib=rb-1.1.0&rect=22%2C5%2C3764%2C2055&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Some parts of the U.S. see well over 100 inches (2.5 meters) of snow per year.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/downhill-sledging-royalty-free-image/488074477?phrase=sledding+in+snow">Edoardo Frola/Moment Open via Getty Images</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
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<blockquote>
<p><strong>How is snow made? – Tenley, age 7, Rockford, Michigan</strong></p>
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<p>The thought of snow can conjure up images of powdery slopes, days out of school or hours of shoveling. For millions of people, it’s an inevitable part of life – but you may rarely stop to think about what made the snow.</p>
<p>As a <a href="https://www.eaps.purdue.edu/people/profile/ablanch.html">professor of atmospheric and planetary sciences</a>, <a href="https://scholar.google.com/citations?user=xClwTzUAAAAJ&hl=en&oi=ao">I’ve studied how ice crystals floating</a> in the sky become the snow that coats the ground.</p>
<p>It all starts in the clouds.</p>
<p>Clouds form when air near the Earth’s surface rises. This happens when sunlight warms the ground and the air closest to it, just like the Sun can warm your face on a cold winter day. </p>
<p>As the slightly warmer air rises, it cools – and the water vapor in that rising air condenses to form liquid water or water ice. From that, <a href="https://climatekids.nasa.gov/cloud-formation/#:%7E">a cloud is born</a>. </p>
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<iframe width="440" height="260" src="https://www.youtube.com/embed/Cf6El0mI1fM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">You need just two things for snow to form.</span></figcaption>
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<h2>Endless pathways</h2>
<p>When temperatures are well below freezing on the ground, the clouds are primarily made of water in the form of ice. Under 32 degrees Fahrenheit – that’s zero degrees Celsius – the frozen water molecules arrange themselves into a hexagonal, or six-sided, crystalline shape. As ice crystals grow and clump together, they become too heavy to stay aloft. With the help of gravity, they begin to fall back down through and eventually out of the cloud.</p>
<p>What these ice crystals look like once they reach land depends on the temperature and humidity of the atmosphere. As the humidity – or the amount of water vapor in the cloud – increases, some of the ice crystals will grow intricate arms at their six corners. That branching process creates what we think of as the <a href="https://www.timeforkids.com/g2/snowflake-science-g2-5-plus/?rl=en-500">characteristic shapes of snowflakes</a>. </p>
<p>No two ice crystals take the same path through a cloud. Instead, every ice crystal experiences different temperatures and humidities as it travels through the cloud, whether going up or down. The ever-changing conditions, combined with the infinite number of paths the crystals could take, result in a unique growth history and crystalline shape for each and every snowflake. This is why you’ve likely heard the saying, “<a href="https://www.willyswilderness.org/post/no-two-snowflakes-are-alike-it-s-actually-true">No two snowflakes are exactly alike</a>.” </p>
<p>Many times, these differences are visible to the naked eye; sometimes a microscope is required to tell them apart. Either way, scientists who study clouds and snow can examine a snowflake and ultimately understand the path it took through the cloud to land on your hand. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Snow crystals attached to a window." src="https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=636&fit=crop&dpr=1 600w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=636&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=636&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=799&fit=crop&dpr=1 754w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=799&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/576901/original/file-20240220-23-n5kry6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=799&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">It takes approximately one hour for a snowflake to reach the ground.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/snowflakes-royalty-free-image/158720307?phrase=snowflakes">LiLi/iStock via Getty Images Plus</a></span>
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<h2>Liquid water as glue</h2>
<p>When snow falls from the sky, you don’t usually see individual ice crystals, but rather clumps of <a href="https://scied.ucar.edu/learning-zone/storms/snowflakes">crystals stuck together</a>. One way ice crystals aggregate is through what’s called mechanical interlocking. When ice crystals bump into each other, crystals with intricate branches and arms intertwine and stick to others. </p>
<p>This mechanism is the main sticking process in cooler, drier conditions – what people call a “<a href="https://compuweather.com/the-important-difference-between-wet-snow-and-dry-snow/">dry snow</a>.” The result is a snow perfect for skiing, and easily picked up by the wind, but that won’t hold together when formed into a snowball. </p>
<p>The second way to stick ice crystals together is to warm them up a bit. When ice crystals fall through a region of cloud or atmosphere where the temperature is slightly above freezing, the edges of the crystals start to melt. Just a tiny bit of liquid water allows ice crystals that bump into each other to stick together very efficiently, almost like glue. </p>
<p>The result? Large clumps of ice crystals falling from the sky, what we call a “<a href="https://www.acurite.com/blog/types-of-snow.html">wet snow</a>” – less than ideal for hitting the slopes but perfect for building a snowman. </p>
<p>Snow formed in clouds typically reaches the ground only in winter. But almost all clouds, no matter the time of year or location, <a href="https://scijinks.gov/clouds/">contain some ice</a>. This is true even for clouds in warm tropical regions, because the atmosphere above us is much colder and can reach temperatures below freezing even on the warmest of days. In fact, scientists who study weather discovered that clouds containing ice produce more rain than those that don’t contain any ice at all.</p>
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<p class="fine-print"><em><span>Alexandria Johnson receives funding from NASA. </span></em></p>There are an infinite number of paths an ice crystal can take before you touch it.Alexandria Johnson, Professor of Atmospheric and Planetary Sciences, Purdue UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2220952024-02-12T16:31:43Z2024-02-12T16:31:43ZForever chemicals in ski wax are being spread on snowy slopes<figure><img src="https://images.theconversation.com/files/574955/original/file-20240212-16-zludm6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A study of the Austrian slopes has found that forever chemicals in ski wax end up on the slopes, in soil and snow.</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/skiing-jumping-skier-extreme-winter-sports-1187224183">Artur Didyk/Shutterstock</a></span></figcaption></figure><p>Every February half-term, I think back to the French ski trips I went on as a teenager. I remember the freshness of the cold, crisp air as I snow-ploughed my way down the slopes. Escaping to somewhere seemingly so pristine felt like a world away from where I grew up in London. </p>
<p>Back then, I never considered that snow could be a potential source of exposure to a harmful chemical. However, recent evidence suggests that persistent, synthetic chemicals are being transferred into snow and soil from waxes applied to the surfaces of skis to enhance performance.</p>
<p>Nicknamed forever chemicals, per- and poly-fluoroalkyl substances (PFAS) are a class of more than <a href="https://www.oecd.org/chemicalsafety/portal-perfluorinated-chemicals/aboutpfass/">10,000 different chemicals</a>, many of which have been used since the 1950s. They repel water and oil so they make great waterproof coatings for clothing, greaseproof paper and construction materials. </p>
<p>Some act as surfactants, allowing different liquids to mix more easily. Many resist high temperatures, so they’re ideal for making non-stick frying pans and firefighting foams. </p>
<p>Certain PFAS are used in ski wax applied to skis and snowboards as lubrication. By making surfaces of ski kit more slippery, skiers can speed up and make smoother turns as they travel from piste to piste. A <a href="https://pubs.rsc.org/en/content/articlelanding/2023/EM/D3EM00375B">new study</a> has found high PFAS concentrations in ski waxes and in the snow and soil sampled from popular skiing areas in Austria.</p>
<h2>The problem with persistence</h2>
<p>PFAS are organoflourine compounds – their super strong carbon-flourine bonds make them incredibly stable. Because PFAS don’t <a href="https://echa.europa.eu/hot-topics/perfluoroalkyl-chemicals-pfas">break down easily</a>, they can persist inside our bodies or in the environment for <a href="https://www.health.pa.gov/topics/Documents/Environmental%20Health/PFAS%20Fact%20Sheet.pdf">many years</a>. </p>
<p>A single dose of perfluorooctanoic acid or PFOA, one of the most well-studied PFAS, could take between three and seven years to reduce by half inside the body – that means it could take 100 years to eliminate 99.9% of that dose. </p>
<p>Some PFAS can be toxic to humans and wildlife, with links to <a href="https://www.thelancet.com/journals/ebiom/article/PIIS2352-3964(23)00397-3/fulltext#:%7E:text=This%20study%20supports%20the%20hypothesis,plastic%20packaging%2C%20etc.">cancers</a>, <a href="https://www.sciencedirect.com/science/article/pii/S0160412022003117">developmental</a> and <a href="https://pubmed.ncbi.nlm.nih.gov/36334833/#:%7E:text=Conclusion%3A%20Based%20on%20the%20evidence,in%20odds%20ratio%20for%20infertility">reproductive problems</a>, <a href="https://www.sciencedirect.com/science/article/abs/pii/S1438463918300476?via%3Dihub">hormone disruption</a>, <a href="https://www.sciencedirect.com/science/article/pii/S0013935123003171#:%7E:text=May%202023%2C%20115525-,Exposure%20to%20high%20levels%20of%20PFAS%20through%20drinking%20water%20is,based%20study%20in%20Ronneby%2C%20Sweden">diabetes</a> and <a href="https://doi.org/10.1002/etc.4890;%20https://doi.org/10.1016/j.scitotenv.2020.144795">obesity</a>. </p>
<figure class="align-center ">
<img alt="Woman in yellow jackets applies wax to four yellow skis laid out on wooden table" src="https://images.theconversation.com/files/574960/original/file-20240212-28-bro51v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/574960/original/file-20240212-28-bro51v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/574960/original/file-20240212-28-bro51v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/574960/original/file-20240212-28-bro51v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/574960/original/file-20240212-28-bro51v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/574960/original/file-20240212-28-bro51v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/574960/original/file-20240212-28-bro51v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The presence of PFAS in ski wax is widely understood - now research shows that the chemicals transfer from ski wax to the environment and end up in snow and soil on the white slopes.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/japanese-senior-woman-waxing-skis-1620325474">Rammy_Rammy/Shutterstock</a></span>
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<h2>A slippery slope?</h2>
<p>The presence of PFAS in ski waxes is not a new discovery. In 2010, a Swedish study, found high levels of various PFAS in ski wax and in the blood of <a href="https://doi.org/10.1021/es9034733">ski-waxing technicians</a>. </p>
<p>The fascinating thing about the new study is the potential for these chemicals to transfer into the environment from recreational and professional skiing equipment. She reveals that PFAS levels in the snow and soil from skiing areas are consistently higher than in those from the control sample collected away from skiing areas, indicating that skiing can act as a source. </p>
<p>The researchers highlight how the PFAS profiles (the combination of different PFAS found in each sample) differed between locations and sample types. This variability was attributed to differences between ski waxes that had been manufactured at different times or in different places. </p>
<p>I would suggest that additional sources of PFAS are likely in these areas, particularly as PFAS were still sometimes detected in areas of no skiing. They are present in some waterproof clothing, which is worn in abundance by skiers, and in food packaging, paints and cabling – all of which will be found in these areas. These products are likely to display different PFAS profiles. </p>
<p>The new study highlights the difficulty of assessing PFAS globally. There are so many different individual PFAS chemicals. So much so that there’s still uncertainty over the true number that <a href="https://time.com/6281242/pfas-forever-chemicals-home-beauty-body-products/">exist</a>. With PFAS in so many products, it’s hard to identify a singular source.</p>
<p>With so many PFAS in circulation, it’s hard to know which ones to test for. The researchers in the new study searched for 34 PFAS chemicals – that’s no easy task. For every PFAS measured, analysis takes more time and money and gets more complicated.</p>
<p>The sum of the concentrations of these 34 PFAS represented less than 1% of the total organofluorine present in the same samples, so the true PFAS concentration could be even higher. </p>
<h2>A class-based approach</h2>
<p>Historically, individual chemicals have been banned depending on toxicity, persistence and resistance to degradation. This has invariably led to the replacement of banned chemicals with structurally similar ones. </p>
<p>Assessing 10,000 PFAS individually would be impossible. PFAS display varying levels of toxicity and persistence with some breaking down <a href="https://doi.org/10.1016/j.yrtph.2022.105226">quite readily</a>, but in recent years, environmental chemists have called for PFAS to be regulated together as a <a href="https://doi.org/10.1039%2Fd0em00147c">group or class</a>. </p>
<p>The European Chemicals Agency is considering a <a href="https://echa.europa.eu/-/echa-publishes-pfas-restriction-proposal">proposed restriction</a> to ban the manufacture and use of PFAS, with some exemptions for essential use where no alternatives exist. If accepted by member states, it could prove a significant step towards the beginning of the end for forever chemicals. Meanwhile, UK legislation <a href="https://www.dwi.gov.uk/pfas-and-forever-chemicals/">falls behind</a> by focusing on individual PFAS, with delays in implementing new restrictions. </p>
<p>Interestingly, PFAS-containing waxes were banned by the International Ski and Snowboard Federation at the start of the 2023 – 2024 season. Norwegian Olympic silver medallist Ragnhild Mowinckel was disqualified last October for competing with fluorinated wax. </p>
<p>But a ban that only applies to professional competition won’t stop PFAS chemicals from reaching the slopes. A ban on the manufacture of PFAS-containing products is crucial. Only then can we prevent PFAS reaching the mountains, and even with a comprehensive ban now, PFAS already in the snow won’t disappear within my lifetime.</p>
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<figure class="align-right ">
<img alt="Imagine weekly climate newsletter" src="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/434988/original/file-20211201-21-13avx6y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p class="fine-print"><em><span>Daniel Drage has previously worked on projects funded by the Natural Environment Research Council and the Environmental Protection Agency of Ireland. He is a Lecturer in Environmental Health at the University of Birmingham, and an Honorary Research Fellow at the University of Queensland (Australia). </span></em></p>Synthetic chemicals found in ski wax have been found in the snow and soil on ski slopes and could pose a toxic threat to the environment.Daniel Drage, Lecturer in Environmental Health, University of BirminghamLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2208182024-02-02T13:17:06Z2024-02-02T13:17:06ZHow can I get ice off my car? An engineer who studies airborne particles shares some quick and easy techniques<figure><img src="https://images.theconversation.com/files/572255/original/file-20240130-29-7n5wna.jpeg?ixlib=rb-1.1.0&rect=0%2C3%2C1024%2C763&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Condensation and cold combine to create that layer of ice on car windshields in winter. </span> <span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File:Oblodzone_szyby_samochodu,_zima_2009_%28ubt%29.jpeg">Tomasz Sienicki/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>If you live somewhere that gets cold in the winter, you’ve probably seen cars parked outdoors covered in a thin layer of ice on a chilly morning. But what causes this frost, and how can you get rid of it quickly?</p>
<p>I’m a <a href="https://scholar.google.com/citations?user=xcpTqRYAAAAJ&hl=en">mechanical engineering professor</a> who studies how water vapor interacts with airborne particles under different atmospheric conditions. Frosty windshields are similar to some of the thermodynamic questions I study in the lab, and they’re also a pesky issue that I deal with every winter on my way to work. </p>
<h2>Windshield condensation</h2>
<p>The air in Earth’s atmosphere always contains a certain amount of water vapor, but there’s only so much water vapor the air can hold. Scientists call that limit 100% <a href="https://www.britannica.com/science/humidity">relative humidity</a>. <a href="https://www.weather.gov/arx/why_dewpoint_vs_humidity">The dew point</a> refers to the temperature at which relative humidity reaches 100%. </p>
<p>Wet air has high dew point temperature, while dry air has a low dew point temperature. With each degree drop in temperature, the air gets closer to its dew point temperature – or its water vapor carrying capacity. Any cooling after the dew point temperature has been reached causes <a href="https://sealevel.jpl.nasa.gov/ocean-observation/understanding-climate/air-and-water/">water to condense onto surfaces</a>, or form into fog.</p>
<p>Overnight, car windshields facing the cold dark sky are <a href="https://www.energy.gov/energysaver/principles-heating-and-cooling">radiatively cooled</a>, meaning they release heat out into their surrounding area in the form of visible and invisible light. As air comes in contact with the cold windshield, it can reach its dew point temperature. Then, the water vapor condenses onto the windshield.</p>
<p>When this radiative cooling drops the temperature on the windshield’s surface to <a href="https://www.britannica.com/science/freezing-point">below the freezing point</a>, 32 degrees Fahrenheit (zero degrees Celsius), the layer of condensed water on the windshield turns to frost. </p>
<h2>Defrosting your car</h2>
<p>To defrost an icy windshield, you can follow a few different approaches, some of which take longer and require more effort than others.</p>
<p>One option is to directly spray a small amount of warm liquid on the layer of frost to help melt it. For this approach to work, the spray liquid must be hot enough to raise the overall temperature of the frost layer to above <a href="https://pubchem.ncbi.nlm.nih.gov/ptable/melting-point/">the melting point</a>. But the temperature can’t be way hotter than the temperature of the glass or you’ll crack your windshield. </p>
<p>A better way to melt the ice without damaging your car is to spray your windows with a warm liquid that has a lower freezing point than water, like a mixture of rubbing alcohol and water. This warm mixture will melt the frost layer without heating up the glass, and the resulting liquid layer on the windshield will have a lower freezing point than water. It will remain liquid, and you can wipe it away with your windshield wipers. </p>
<p>Similar alcohol and water mixtures – <a href="https://www.britannica.com/science/glycol">glycol, for example</a> – are commonly used to maintain the <a href="https://mayekawa.es/images/pdf/ASHRAE_ENERGY_EFFICIENT_ICE_RINK_2015.pdf">icy surface of skating rinks</a>.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/A2Kl04dHm4k?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A mix of water and rubbing alcohol can melt ice on your windshield.</span></figcaption>
</figure>
<p>This approach can melt the ice reasonably quickly and easily, without too much effort. You don’t even have to turn on your car. </p>
<p>If you have a little more time, you can start the car and run <a href="https://www.lifewire.com/how-do-car-defrosters-work-534663">the air defrost system</a> to blow hot air – aim for above 80 degrees Fahrenheit – onto the inside of the windshield. This warms the windshield and will eventually melt the frost layer. Once you see some melting, you can use the windshield wipers to wipe the rest of the ice away. </p>
<p>This option consumes more energy, as your car will have to heat up the windshield, but it doesn’t require you to do much. </p>
<p>Using the defrost system to blow warm air toward the windshield will also help to clear the inside of the windshield when it gets fogged up from condensation. Otherwise, if it’s dry outside, you can also clear up windshield fog by opening the car window and letting in outside air.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A person wearing a winter jacket uses a scraper on their frost-covered windshield." src="https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=396&fit=crop&dpr=1 600w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=396&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=396&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=497&fit=crop&dpr=1 754w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=497&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/572257/original/file-20240130-23-r3f30r.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=497&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">You can use an ice scraper to break the ice on your windshield into chunks, so your wiper blades can clean them off.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/ColoradoWeather/c8d71e03eb5144afad7c01e72eccf5c2/photo?Query=windshield%20wipers&mediaType=photo&sortBy=&dateRange=Anytime&totalCount=296&digitizationType=Digitized&currentItemNo=17&vs=true&vs=true">AP Photo/David Zalubowski</a></span>
</figcaption>
</figure>
<p>If you are in a hurry or need some exercise, you can use an ice scraper to break up frost on your windshield, creating smaller islands of ice. The windshield wiper can then mechanically dislodge the chunks by moving them around and melting them. This requires more energy on your part, but it doesn’t require much from your car.</p>
<p>If you have a relaxed start to your day, you can let the Sun warm the windshield and slowly melt the frost layer for you. This technique saves energy in every way imaginable.</p><img src="https://counter.theconversation.com/content/220818/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Suresh Dhaniyala does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>When you’re running late in the winter, you don’t want to have to spend time scraping frost off your windshield. Try some expert-recommended techniques instead.Suresh Dhaniyala, Bayard D. Clarkson Distinguished Professor of Mechanical and Aeronautical Engineering, Clarkson UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2222492024-01-30T13:36:20Z2024-01-30T13:36:20ZWhat is an atmospheric river? With flooding and mudslides in California, a hydrologist explains the good and bad of these storms and how they’re changing<figure><img src="https://images.theconversation.com/files/572509/original/file-20240131-15-zr0n4c.jpg?ixlib=rb-1.1.0&rect=164%2C18%2C2084%2C1425&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A satellite image shows a powerful atmospheric river hitting the U.S. West Coast on Jan. 31, 2024.</span> <span class="attribution"><a class="source" href="https://cdn.star.nesdis.noaa.gov/GOES18/ABI/CONUS/GEOCOLOR/20240311721_GOES18-ABI-CONUS-GEOCOLOR-2500x1500.jpg">NOAA GOES</a></span></figcaption></figure><p><em>Millions of Californians were <a href="https://www.nbcnews.com/news/weather/live-blog/potentially-life-threatening-storm-system-begins-pounding-california-l-rcna137204">under flood alerts</a> as a <a href="https://cw3e.ucsd.edu/cw3e-ar-update-2-february-2024-outlook/">powerful atmospheric river</a> brought heavy rain to the West Coast in early February 2024. Los Angeles saw <a href="https://images.theconversation.com/files/573527/original/file-20240205-19-ss87hh.png">one of its wettest days on record</a> with over 4 inches of rain on Feb. 4. Other communities were hit by more than 12 inches of rain and reported <a href="https://ktla.com/news/local-news/live-updates-worst-of-storm-moves-into-southern-california/">widespread flooding</a>. <a href="https://www.youtube.com/watch?v=qCEX7nwXwaI">Debris and mudslides</a> shut down <a href="https://twitter.com/CaltransDist7/status/1754525910676697306">sections of highways</a> and <a href="https://laist.com/news/climate-environment/major-storm-heading-into-socal-sunday">roads into Malibu</a>.</em> </p>
<p><em>It was the <a href="https://cw3e.ucsd.edu/cw3e-ar-update-29-january-2024-outlook/">latest in a series</a> of atmospheric rivers to bring extreme rainfall to the West Coast. While these storms are dreaded for the damage they can cause, they are also essential to the region’s water supply, particularly in California, as <a href="https://scholar.google.com/citations?user=aTFYE98AAAAJ&hl=en">Qian Cao</a>, a hydrologist at the University of California, San Diego, explains.</em></p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1754534734300885206"}"></div></p>
<h2>What are atmospheric rivers?</h2>
<p>An atmospheric river is a narrow corridor or filament of concentrated water vapor transported in the atmosphere. It’s like a river in the sky that can be <a href="https://pubs.usgs.gov/publication/70036359">1,000 miles long</a>. On average, atmospheric rivers have about <a href="https://www.jpl.nasa.gov/news/ranking-atmospheric-rivers-new-study-finds-world-of-potential">twice the regular flow of the Amazon River</a>.</p>
<p>When atmospheric rivers run up against mountains or run into local atmospheric dynamics and are forced to ascend, the moisture they carry cools and condenses, so they can produce intense rainfall or snowfall.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/w3rtYM0HtIM?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">A satellite view of atmospheric rivers.</span></figcaption>
</figure>
<p>Atmospheric rivers occur all over the world, most commonly in the mid-latitudes. They form when large-scale weather patterns align to create narrow channels, or filaments, of intense moisture transport. These start over warm water, typically tropical oceans, and are guided toward the coast by low-level jet streams ahead of cold fronts of extratropical cyclones.</p>
<p>Along the U.S. West Coast, the Pacific Ocean serves as the reservoir of moisture for the storm, and the mountain ranges act as barriers, which is why the western sides of the coastal ranges and Sierra Nevada see so much rain and snow.</p>
<h2>Why are back-to-back atmospheric rivers a high flood risk?</h2>
<p>Consecutive atmospheric rivers, known as AR families, <a href="https://doi.org/10.1175/JHM-D-18-0217.1">can cause significant flooding</a>.</p>
<p>The first heavy downpours saturate the ground. As <a href="https://doi.org/10.1126/sciadv.abq0995">consecutive storms arrive</a>, their precipitation falls on soil that can’t absorb more water. That contributes to more runoff. Rivers and streams fill up. In the meantime, there may be snowmelt due to warm temperatures, further adding to the runoff and flood risk.</p>
<p>California experienced a <a href="https://theconversation.com/epic-snow-from-all-those-atmospheric-rivers-in-the-west-is-starting-to-melt-and-the-flood-danger-is-rising-203874">historic run</a> of nine consecutive atmospheric rivers in the span of three weeks in December 2022 and January 2023. The storms <a href="https://theconversation.com/is-the-western-drought-finally-ending-that-depends-on-where-you-look-201156">helped bring most reservoirs back</a> to historical averages in 2023 after several drought years, but they also produced damaging <a href="https://www.cbsnews.com/news/california-flooding-landslides-as-atmospheric-river-power-outage">floods and debris flows</a>.</p>
<figure class="align-center ">
<img alt="An animation shows filaments of water heading toward the coast." src="https://images.theconversation.com/files/572019/original/file-20240129-21-24vhfq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/572019/original/file-20240129-21-24vhfq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=282&fit=crop&dpr=1 600w, https://images.theconversation.com/files/572019/original/file-20240129-21-24vhfq.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=282&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/572019/original/file-20240129-21-24vhfq.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=282&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/572019/original/file-20240129-21-24vhfq.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=354&fit=crop&dpr=1 754w, https://images.theconversation.com/files/572019/original/file-20240129-21-24vhfq.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=354&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/572019/original/file-20240129-21-24vhfq.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=354&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Atmospheric rivers forming over the tropical Pacific Ocean head for the U.S. West Coast.</span>
<span class="attribution"><a class="source" href="https://www.nps.gov/articles/images/AR-animation.gif">NOAA</a></span>
</figcaption>
</figure>
<p>The cause of AR families is an active area of research. Compared with single atmospheric river events, AR families tend to be associated with lower atmospheric pressure heights across the North Pacific, higher pressure heights over the subtropics, a stronger and more zonally elongated jet stream and warmer tropical air temperatures. </p>
<p>Large-scale weather patterns and climate phenomena such as the <a href="https://www.climate.gov/news-features/blogs/enso/what-mjo-and-why-do-we-care">Madden-Julian Oscillation</a>, or MJO, <a href="https://doi.org/10.1175/BAMS-D-22-0208.1">also play an important role</a> in the generation of AR families. An active MJO shift occurred during the early 2023 events, tilting the odds toward increased atmospheric river activity over California.</p>
<figure class="align-center ">
<img alt="A truck drives through muddy streets that fill a large section of town. People stand on one small patch of pavement not flooded." src="https://images.theconversation.com/files/572098/original/file-20240130-21-dc67s7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/572098/original/file-20240130-21-dc67s7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=336&fit=crop&dpr=1 600w, https://images.theconversation.com/files/572098/original/file-20240130-21-dc67s7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=336&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/572098/original/file-20240130-21-dc67s7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=336&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/572098/original/file-20240130-21-dc67s7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/572098/original/file-20240130-21-dc67s7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/572098/original/file-20240130-21-dc67s7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An aerial view shows a flooded neighborhood in the community of Pajaro in central California on March 11, 2023, after a series of atmospheric rivers.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/an-aerial-view-shows-a-flooded-neighborhood-in-the-news-photo/1248039581">Josh Edelson/AFP via Getty Images</a></span>
</figcaption>
</figure>
<p>A recent study by scientists at Stanford and the University of Florida found that storms within AR families <a href="https://www.science.org/doi/10.1126/sciadv.adi7905">cause three to four times more economic damage</a> when the storms arrive back to back than they would have caused by themselves.</p>
<h2>How important are atmospheric rivers to the West Coast’s water supply?</h2>
<p>I’m a research hydrologist, so I focus on hydrological impacts of atmospheric rivers. Although they can lead to flood hazards, atmospheric rivers are also essential to the Western water supply. Atmospheric rivers have been responsible for ending <a href="https://doi.org/10.1175/JHM-D-13-02.1">more than a third</a> of the region’s major droughts, including the severe California drought of 2012-16.</p>
<p>Atmospheric rivers provide an average of <a href="https://doi.org/10.1111/j.1752-1688.2011.00546.x">30% to 50% of the West Coast’s annual precipitation</a>. </p>
<p>They also contribute to the snowpack, which provides a significant portion of California’s year-round water supply. </p>
<p>In an average year, one to two extreme atmospheric rivers with snow will be the dominant contributors to the snowpack in the Sierra Nevada. Together, atmospheric rivers will <a href="https://doi.org/10.1029/2010GL044696">contribute about 30% to 40%</a> of an average season’s total snow accumulation there.</p>
<figure class="align-center ">
<img alt="A dam spillway with a full reservoir behind it." src="https://images.theconversation.com/files/572102/original/file-20240130-15-f4mjgk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/572102/original/file-20240130-15-f4mjgk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=382&fit=crop&dpr=1 600w, https://images.theconversation.com/files/572102/original/file-20240130-15-f4mjgk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=382&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/572102/original/file-20240130-15-f4mjgk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=382&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/572102/original/file-20240130-15-f4mjgk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=481&fit=crop&dpr=1 754w, https://images.theconversation.com/files/572102/original/file-20240130-15-f4mjgk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=481&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/572102/original/file-20240130-15-f4mjgk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=481&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">After several winter storms brought record snowfall to California’s Sierra Nevada in early 2023, Lake Oroville, California’s second-largest reservoir, was at 100% capacity. The previous year, much of the state had faced water restrictions.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/in-an-aerial-view-water-is-released-on-the-main-spillway-at-news-photo/1498829327">Justin Sullivan/Getty Images</a></span>
</figcaption>
</figure>
<p>That’s why my colleagues at the <a href="https://cw3e.ucsd.edu/">Center for Western Weather and Water Extremes</a> at the Scripps Institution of Oceanography, part of the University of California, San Diego, work on <a href="https://doi.org/10.1175/BAMS-D-22-0208.1">improving atmospheric river forecasts and predictions</a>. Water managers need to be able to regulate reservoirs and figure out how much water they can save for the dry season while still leaving room in the reservoirs to manage flood risk from future storms.</p>
<h2>How is global warming affecting atmospheric rivers?</h2>
<p>Warmer air can <a href="https://theconversation.com/climate-change-is-intensifying-the-water-cycle-bringing-more-powerful-storms-and-flooding-heres-what-the-science-shows-187951">hold more moisture</a>. As global temperatures rise in the future, we can expect more intense atmospheric rivers, leading to an <a href="https://doi.org/10.1038/s41598-019-46169-w">increase in heavy and extreme precipitation events</a>. </p>
<p>My research also shows that more atmospheric rivers are <a href="https://doi.org/10.1175/JHM-D-19-0242.1">likely to occur concurrently during already wet conditions</a>. So, the chance of extreme flooding also increases. Another study, by scientists from the University of Washington, suggests that there will be a <a href="https://doi.org/10.1175/JHM-D-16-0200.1">seasonal shift</a> to more atmospheric rivers earlier in the rainy season.</p>
<p>There will likely also be more <a href="https://doi.org/10.1038/s41598-019-46169-w">year-to-year variability</a> in the total annual precipitation, particularly in California, as a study by my colleagues at the Center for Western Weather and Water Extremes projects.</p>
<p><em>This article was update Feb. 5, 2024, with flooding and mudslides in California.</em></p><img src="https://counter.theconversation.com/content/222249/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Qian Cao does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>These giant rivers in the sky are both destructive and essential for the Western U.S. water supply.Qian Cao, Hydrologist, Center for Western Weather and Water Extremes, University of California, San DiegoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2209432024-01-11T13:26:43Z2024-01-11T13:26:43ZTahoe avalanches: What causes innocent-looking snow slopes to collapse? A physicist and skier explains, with tips for surviving<figure><img src="https://images.theconversation.com/files/568796/original/file-20240111-19-upafl3.jpg?ixlib=rb-1.1.0&rect=0%2C2438%2C3304%2C2022&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A skier at Palisades Tahoe, home of the 1960 Winter Olympics and site of a small but deadly avalanche in 2024.</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/SnowboundSierra/fa093ab6ef4849ad990f949d64a2887a/photo">AP Photo/Rich Pedroncelli</a></span></figcaption></figure><p><em>An avalanche <a href="https://www.kcra.com/article/avalanche-palisades-tahoe-resort-palisades-side/46342439/">swept up skiers</a> at Lake Tahoe’s largest ski resort on Jan. 10, 2024, as a 150-foot-wide sheet of snow slid down a mountain slope into a pile 10 feet deep. One person died in the avalanche and three others were rescued, according to the <a href="https://www.kcra.com/article/avalanche-palisades-tahoe-resort-palisades-side/46342439">Placer County, California, Sheriff’s Office</a>. The slide happened in steep terrain near the <a href="https://snowbrains.com/kt-22-palisades-tahoe-best-chairlift-north-america/">KT-22 chairlift</a>, which had just opened for the season that morning. A <a href="https://www.kcra.com/article/palisades-tahoe-resort-second-avalanche-reported/46356367">second unplanned avalanche</a> hit the same ski resort the next day, but no one was injured.</em> </p>
<p><em>Avalanche deaths are <a href="https://avalanche.state.co.us/accidents/us">rare inbounds</a> at ski resorts like Palisades Tahoe, but the risk rises in the backcountry – 30 backcountry avalanche deaths were reported in the U.S. during the 2022-2023 season. <a href="https://scholar.google.co.uk/citations?user=bWUANQMAAAAJ&hl=en">Nathalie Vriend</a>, a skier and physicist at the University of Colorado Boulder who studies avalanches, explains what happens in an avalanche and techniques for surviving one.</em></p>
<h2>What causes avalanches?</h2>
<p>The behavior of an avalanche depends on the structure of the snowpack, but that’s only one ingredient. An avalanche requires all the wrong conditions at the wrong time.</p>
<p>The angle of the mountain slope is important. Slopes between <a href="https://avalanche.ca/glossary/terms/slope-angle">25 and 40 degrees</a> run the greatest risk of avalanches. Those are also ideal for skiing, of course. If the slope is less than 25 degrees, there might be little slips, but the snow won’t pick up speed. If it’s over 40 degrees, the snow typically cannot accumulate, clearing away the avalanche risk.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/oKTUw78thcg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Avalanche awareness for backcountry skiers.</span></figcaption>
</figure>
<p>Then there needs to be a trigger. A snowpack may be seemingly stable until a snowmobile or skier disturbs it enough that the snow starts to move. Strong winds or rock falls may also cause an avalanche. Blowing snow can create wind loading and <a href="https://avalanche.org/avalanche-encyclopedia/avalanche/avalanche-problems/avalanche-problem-type/cornice-fall/">build up into cornices</a>, creating an overhang that can eventually fall and trigger an avalanche below.</p>
<h2>What happens inside the snowpack during an avalanche?</h2>
<p>Mountain snowpack isn’t uniform. Because it builds up over time, it is a snapshot of recent weather conditions and has both stable and weak layers.</p>
<p>When snow falls, it’s a fluffy crystal structure. But when the temperature rises and the snow starts to melt and then refreezes, it <a href="https://avalanche.org/avalanche-encyclopedia/snowpack/weak-layer/persistent-weak-layers/depth-hoar-basal-facets/">turns more granular</a>.</p>
<p>That granular, icier snow is a <a href="https://avalanche.ca/glossary/terms/persistent-weak-layer">weak layer</a>. When a new snowfall dumps on top of it, the grains in the weak layer can shear, creating a surface for an avalanche to slide on. The weight of new snowpack can cause the entire face of a mountain to fall away almost instantaneously. As the avalanche picks up speed, more snow and debris are incorporated in the avalanche and it can become really big and violent.</p>
<figure class="align-center ">
<img alt="A domed mountain with snow clearly slid down the full width of one side." src="https://images.theconversation.com/files/568793/original/file-20240111-23-axxbv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/568793/original/file-20240111-23-axxbv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/568793/original/file-20240111-23-axxbv4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/568793/original/file-20240111-23-axxbv4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/568793/original/file-20240111-23-axxbv4.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=565&fit=crop&dpr=1 754w, https://images.theconversation.com/files/568793/original/file-20240111-23-axxbv4.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=565&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/568793/original/file-20240111-23-axxbv4.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=565&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An avalanche takes down the side of a mountain near Winter Park, Colo., in 2021.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/Rockies-AvalancheDanger/ebc1137f30c54ec29eace5443635401f/photo">Colorado Avalanche Information Center via AP</a></span>
</figcaption>
</figure>
<p>In <a href="https://www.colorado.edu/mechanical/nathalie-m-vriend">my lab</a> at the University of Colorado at Boulder, I study small-scale laboratory avalanches. We use a technique called <a href="https://iopscience.iop.org/book/mono/978-0-7503-2472-4/chapter/bk978-0-7503-2472-4ch1">photoelasticity</a> and create thin avalanches to reveal <a href="https://doi.org/10.1103/PhysRevE.100.012902">what’s going on inside the avalanche</a>. We track photoelastic particles with a high-speed camera and can observe that particles bounce and collide really fast, within 1/1,000th of a second.</p>
<p>In a real avalanche, those violent collisions create a lot of heat through friction, which causes more melting. As the avalanche comes to a rest, this liquid can quickly refreeze again, locking the snowpack in place like concrete. People say “<a href="https://www.getprepared.gc.ca/cnt/hzd/vlchs-drng-en.aspx">swim to the surface</a>” in an avalanche, but you may not know whether the surface is up or down. If the avalanche is still moving and the granules haven’t frozen solid again, you might be able to move slightly, but it is really hard.</p>
<h2>What can skiers do if they’re in an avalanche?</h2>
<p>I’ve done fieldwork on real snow avalanches triggered intentionally in Switzerland. We were in a bunker in a valley, and they dropped explosives at the top of the mountain. Using radar, we could look inside the avalanche as it came toward us. It was easily going more than <a href="https://doi.org/10.1002/grl.50134">110 miles per hour (50 meters per second)</a>.</p>
<p>Even if the avalanche is small, you can’t outski or outrun it easily. The big danger is when the snow is deep – you could be buried under several feet of snow. Basically, as the avalanche slows down, new snow keeps piling on top of you. People report this as being trapped in concrete without an ability to even move a limb. It must be a very frightening experience.</p>
<figure class="align-center ">
<img alt="A yellow dog pulls on a tug held by a man in ski patrol outfit and goggles who is buried up to his waist in snow." src="https://images.theconversation.com/files/568870/original/file-20240111-19-oh7pq3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/568870/original/file-20240111-19-oh7pq3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/568870/original/file-20240111-19-oh7pq3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/568870/original/file-20240111-19-oh7pq3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/568870/original/file-20240111-19-oh7pq3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/568870/original/file-20240111-19-oh7pq3.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/568870/original/file-20240111-19-oh7pq3.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An avalanche rescue dog tugs on a ski patrol member during avalanche training at Copper Mountain in Colorado.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/mason-pulls-on-a-tug-held-by-ski-patroller-matt-urich-as-news-photo/1131269864">AAron Ontiveroz/MediaNews Group/The Denver Post via Getty Images</a></span>
</figcaption>
</figure>
<p>Backcountry skiers carry <a href="https://catamounttrail.org/bc-zones/safety-in-the-backcountry/">tools that can increase their chances of survival</a>. Your best bet, though, is your peers – particularly in the backcountry, where emergency crews will take hours to arrive.</p>
<p>There are a few things you can do. First, <a href="https://www.youtube.com/watch?v=nnHXLVA2FcE">carry a transceiver</a>, which transmits a signal identifying your location. When you are caught in an avalanche, you are transmitting a signal. Your friends can switch their transceivers to the “receiving” mode and try to locate your beacon. It’s also important to have an avalanche probe and a shovel in the backcountry for when your friends do locate your position: The snow is like concrete, and it will be hard to extract you.</p>
<p><a href="https://www.youtube.com/watch?v=jOE9b60TsT4">Avalanche air bags</a> can also help – James Bond <a href="https://www.youtube.com/watch?v=MQQLqRYm4vg">used an elaborate concept of one</a> in “The World Is Not Enough.” With modern avalanche air bags, you pull a toggle on your back, and the air bag inflates behind your head, <a href="https://youtu.be/h7QFRXc0R8M?feature=shared">turning you into a bigger particle</a>. Bigger particles tend to stay at the surface, making you easier to locate.</p>
<h2>How is avalanche risk changing as winter temperatures rise?</h2>
<p>It’s an important question, and it’s not as simple as warming temperatures mean less snow, so fewer avalanches. Instead, if mountains have more variation in temperatures, they may have more melting and refreezing phases during the winter, creating weaker snowpacks compared with historical records.</p>
<p>The historical conditions that communities have grown up around can change. In 2017, there was a big <a href="https://www.gq.com/story/the-avalanche-that-ate-hotel-rigopiano">avalanche in Italy</a> that took out an entire hotel. It was in an area where people didn’t expect an avalanche, based on historical data.</p>
<p>There are computer models that can calculate where avalanches are likely to occur. But when temperatures, snowfall and precipitation patterns change, you may not be able to truly understand cause and effect on natural hazards like snow avalanches. </p>
<p><em>This article was updated with a second avalanche on Jan. 11, 2024.</em></p><img src="https://counter.theconversation.com/content/220943/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Nathalie Vriend receives funding from the Moore Foundation, and in the past from the Royal Society and NERC among others. </span></em></p>A deadly avalanche at Palisades Tahoe, home of the 1960 Winter Olympics, shows the risk as snow layers melt and new snow falls.Nathalie Vriend, Associate Professor of Thermo Fluid Sciences, University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2207542024-01-11T13:26:11Z2024-01-11T13:26:11ZBlizzards are inescapable − but the most expensive winter storm damage is largely preventable<figure><img src="https://images.theconversation.com/files/568721/original/file-20240110-17-o6v3sj.jpg?ixlib=rb-1.1.0&rect=0%2C11%2C3955%2C2616&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Wrecks during snowstorms can shut down highways, stranding drivers in the cold for hours.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/wyomissing-pa-a-tow-truck-works-on-freeing-a-stuck-tractor-news-photo/1303555959">Ben Hasty/MediaNews Group/Reading Eagle via Getty Images</a></span></figcaption></figure><p>Winter storms can easily become <a href="https://www.munichre.com/en/risks/natural-disasters/winter-storms.html">billion-dollar disasters</a> as the snow piles up on interstates and collapses roofs and power lines. Yet, while canceled flights and business interruptions can’t be avoided, what turns a snowstorm into a disaster often can be.</p>
<p><a href="https://scholar.google.com/citations?hl=en&user=2naNhTEAAAAJ">I have worked on engineering strategies</a> to enhance disaster resilience for over three decades and recently wrote a book, “<a href="https://rowman.com/ISBN/9781633888234/The-Blessings-of-Disaster-The-Lessons-That-Catastrophes-Teach-Us-and-Why-Our-Future-Depends-on-It">The Blessings of Disaster</a>,” about the gambles humans take with disaster risk. Snowstorms stand out for how preventable much of the damage really is.</p>
<h2>Stay off the roads</h2>
<p>The easiest storm costs to avoid involve human behavior, including driving during snowstorms.</p>
<p>Successfully plowing the snow off a highway requires repeated passes to prevent snow from accumulating to the point where it piles up faster than it can be removed. However, that simple concept breaks down when an accident blocks the lanes, and traffic – including commerce and emergency vehicles – grinds to a halt.</p>
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<p>When it takes snowmobiles to reach stranded drivers, the wait can be long and in <a href="https://www.kiro7.com/news/trending/woman-dies-after-getting-trapped-car-18-hours-by-snow-family-says/DVPZD7LWW5G6FL2TAIHX3VZPEE/">some cases lethal</a>. Hundreds of people were <a href="https://www.reuters.com/markets/commodities/drivers-trapped-cars-after-us-snowstorm-shuts-major-road-virginia-2022-01-04/">stranded for up to 24 hours</a> on Interstate 95 during a snowstorm in Virginia in 2022.</p>
<p>Unfortunately, partly due to economic pressures, many people won’t stay home during a blizzard unless authorities close the roads or impose driving bans. Those who venture out should <a href="https://www.weather.gov/ilx/winter_drive2_social">be prepared to survive hours in the cold</a> and have proper gear to avoid <a href="https://www.livescience.com/6008-person-freeze-death.html">freezing to death</a>. It’s one reason the <a href="https://www.startribune.com/shorts-in-winter-why-some-minnesotans-stick-to-their-summer-finest/566656091/">fad of wearing shorts</a>, T-shirt and <a href="https://www.psucollegian.com/news/borough/why-do-penn-state-students-wear-shorts-during-the-winter/article_26c0d230-0c39-11e8-9b39-3bbbaf5414bc.html">flip-flops in winter</a> is ill-advised.</p>
<h2>Pay attention to roofs</h2>
<p>One snowflake at a time, wet snow can pile up to a weight of 30 pounds per cubic foot on a rooftop – enough to collapse a structure that is too light or not well designed. Although roof collapses are <a href="https://doi.org/10.1061/(ASCE)CF.1943-5509.0000222">relatively rare</a>, they are expensive and can take months to repair.</p>
<p>How snow builds up on a roof depends on a variety of factors, including the height of the snow accumulation and whether anything prevents the snow from blowing or sliding away.</p>
<figure class="align-center ">
<img alt="A vehicle drives past a show with the roof bowed all the way to the ground with a thick layer of snow on top." src="https://images.theconversation.com/files/568714/original/file-20240110-15-hir48o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/568714/original/file-20240110-15-hir48o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=425&fit=crop&dpr=1 600w, https://images.theconversation.com/files/568714/original/file-20240110-15-hir48o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=425&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/568714/original/file-20240110-15-hir48o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=425&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/568714/original/file-20240110-15-hir48o.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=534&fit=crop&dpr=1 754w, https://images.theconversation.com/files/568714/original/file-20240110-15-hir48o.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=534&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/568714/original/file-20240110-15-hir48o.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=534&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Heavy snow in 2014 collapsed this automotive shop’s roof in Hamburg, N.Y.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/WintryWeather/959b64339c3c49c5b6585aee615c6b51/photo">AP Photo/Mike Groll</a></span>
</figcaption>
</figure>
<p>Building codes specify the minimum snow weights that roofs must be able to handle to be safe. These have been updated over decades to minimize the risk of roofs failing, and they are <a href="https://www.structuremag.org/?p=19724">still improving</a>.</p>
<p>The national maps used to compute minimum snow loads were <a href="https://www.structuremag.org/?p=19528">updated in 2022</a> to include 30 years of additional snow load data. As a result, the amount of snow that new building designs <a href="https://steeljoist.org/wp-content/uploads/2022/02/SJI_Feb_Webinar_SnowLoads_022122_1Slide.pdf">should be able to handle</a> is up to <a href="https://assets.ccaps.umn.edu/documents/CPE-Conferences/structural/2022Structural722ASCE.pdf">80% larger than before</a> in some locations and as much as 40% less in others. For example, snow loads for new construction in New York City; Baltimore; Washington, D.C.; Reno, Nevada; Casper, Wyoming; and Beckley, West Virginia, are all significantly higher now than in the past.</p>
<p>Unfortunately, many cities and states have no buildings codes or have outdated ones. In 2022, the Federal Emergency Management Agency scored each state based on the stringency of its building codes on a 100-point scale, and <a href="https://www.scientificamerican.com/article/most-states-are-failing-on-building-codes-fema-says/">19 states received a score of 0</a>.</p>
<figure class="align-center ">
<img alt="Two men shovel snow off a roof. The snow is is higher than their waists." src="https://images.theconversation.com/files/568713/original/file-20240110-21-v76dmp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/568713/original/file-20240110-21-v76dmp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=395&fit=crop&dpr=1 600w, https://images.theconversation.com/files/568713/original/file-20240110-21-v76dmp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=395&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/568713/original/file-20240110-21-v76dmp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=395&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/568713/original/file-20240110-21-v76dmp.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=496&fit=crop&dpr=1 754w, https://images.theconversation.com/files/568713/original/file-20240110-21-v76dmp.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=496&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/568713/original/file-20240110-21-v76dmp.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=496&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Shoveling snow from rooftops is dangerous, but the weight of too much snow can collapse a weak or older roof.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/WintryWeatherPhotoGallery/4ac5affce0ca47148de8d5427e0af75d/photo">AP Photo/Gary Wiepert</a></span>
</figcaption>
</figure>
<p>To help them improve, <a href="https://www.scientificamerican.com/article/fema-offers-every-state-2-million-to-adopt-safer-building-codes/">FEMA is offering every state $2 million</a> this year to spend on enhancing its existing codes, studying new codes or training employees in using codes.</p>
<p>Better building codes help improve new construction, but older homes and buildings may still be at risk of a possible roof collapse during a heavy snowstorm.</p>
<p>Homeowners and business owners have a few options: Invest in an <a href="https://www.fema.gov/sites/default/files/documents/fema957_snowload_guide.pdf">engineering assessment of the existing roof</a> and then strengthen the roof if needed. Have a team on standby to shovel snow off the roof, which <a href="https://www.fema.gov/sites/default/files/2020-07/fema_snow_load_2014.pdf">can be dangerous</a> and a <a href="https://www.wje.com/knowledge/webinars/detail/snow-loads-webinar">major undertaking</a> for the flat roofs of large warehouse and industrial facilities, for example. Or gamble on insurance covering the full cost of repairs. </p>
<p><iframe id="eHNPp" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/eHNPp/2/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>Prepare for power outages</h2>
<p>When it comes to infrastructure failure during snowstorms, power outages can be the biggest problem.</p>
<p>In 1998, an ice storm dumped freezing rain and drizzle for more than 80 hours on parts of eastern Canada and the Northeastern United States. As ice accumulated to as much as 3 to 4 inches near Montreal, <a href="https://www.wqad.com/article/weather/how-ice-storms-impact-the-power-grid/526-d582a4d4-c336-4422-a18e-5d1e0a7d0da8">the weight</a> snapped tree branches, caused power lines to collapse and <a href="https://www.weather.gov/btv/25th-Anniversary-of-the-Devastating-1998-Ice-Storm-in-the-Northeast">crumpled hundreds of transmission towers</a>, leaving more than <a href="http://news.hydroquebec.com/en/press-releases/1313/twenty-years-ago-quebec-was-battered-by-an-ice-storm/">3 million people there without power for several days</a> in early January. In large parts of Montreal’s South Shore, <a href="https://en.wikipedia.org/wiki/January_1998_North_American_ice_storm">150,000 people were without power for up to three weeks</a> following the storm.</p>
<p>Winter storm Uri in 2021 was even more destructive, as it knocked out power in Texas and froze several other states, causing about US$<a href="https://www.munichre.com/en/risks/natural-disasters/winter-storms.html">30 billion in losses</a> – only about half of that insured.</p>
<p>Nearly everything today depends on reliable power – infrastructure systems, companies, vehicles and even agriculture. When the power failed during the 1998 storm, heating and ventilation systems stopped working. Pipes burst. <a href="https://www.cbc.ca/news/canada/ice-storm-devastates-farm-livestock-1.165771">Farm animals froze to death or died of asphyxiation by the thousands</a>.</p>
<figure class="align-center ">
<img alt="A police car blocks a road where an ice-covered powerline has fallen." src="https://images.theconversation.com/files/568712/original/file-20240110-27-nsu57k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/568712/original/file-20240110-27-nsu57k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=385&fit=crop&dpr=1 600w, https://images.theconversation.com/files/568712/original/file-20240110-27-nsu57k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=385&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/568712/original/file-20240110-27-nsu57k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=385&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/568712/original/file-20240110-27-nsu57k.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=484&fit=crop&dpr=1 754w, https://images.theconversation.com/files/568712/original/file-20240110-27-nsu57k.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=484&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/568712/original/file-20240110-27-nsu57k.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=484&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Ice storms like this one in the Northeast in 2018 can take down miles of power lines, causing blackouts.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/NortheastStorm/177f72669ed14f50b91ae0bb363444e6/photo">AP Photo/Steven Senne</a></span>
</figcaption>
</figure>
<p>Many industry sectors depend on the existing power infrastructure and operate without redundancy that could keep them running when the power goes out. While these optimized systems are slim, efficient and cost-effective – all good things under normal operating conditions – they are not resilient. Resilience, which is the ability to withstand or to recover quickly from extreme events, benefits from having a Plan B ready to deploy.</p>
<p>Power utilities nationwide have tree-trimming programs to minimize the risk of storms bringing branches down on power lines, and some <a href="https://www.fema.gov/case-study/overhead-underground-it-pays-bury-power-lines">utilities are burying power lines</a>, but power outages are still expected. Businesses and homeowners having a Plan B can minimize the risk of costly losses. Insulating water pipes can help avoid the risk of pipes bursting. Backup generators can help if operated safely to avoid hazards <a href="https://www.cpsc.gov/Newsroom/News-Releases/2007/CPSC-Warns-Winter-Storm-Victims-Use-Portable-Generators-Outdoors-Only1">such as fires and carbon monoxide poisoning</a>.</p>
<p>In short, staying off roads, under a roof that can handle the snow, and being prepared for what could be long power outages would help make snowstorms a day off rather than a disaster.</p><img src="https://counter.theconversation.com/content/220754/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michel Bruneau does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Costs quickly rise when things go wrong with roads, roofs and power lines. Many of those risks are also avoidable.Michel Bruneau, Professor of Engineering, University at BuffaloLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2172552024-01-04T13:48:42Z2024-01-04T13:48:42ZThe chickadee in the snowbank: A ‘canary in the coal mine’ for climate change in the Sierra Nevada mountains<figure><img src="https://images.theconversation.com/files/564542/original/file-20231208-19-uw3l7c.jpg?ixlib=rb-1.1.0&rect=0%2C148%2C4139%2C2775&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mountain chickadees struggle with snow extremes.</span> <span class="attribution"><span class="source">Benjamin Sonnenberg</span></span></figcaption></figure><p>Wet snow pelts my face and pulls against my skis as I climb above 8,000 feet in the Sierra Nevada of eastern California, tugging a sled loaded with batteries, bolts, wire and 40 pounds of sunflower seeds critical to our mountain chickadee research.</p>
<p>As we reach the remote research site, I duck under a tarp and open a laptop. A chorus of identification numbers are shouted back and forth as fellow behavioral ecologist <a href="https://scholar.google.com/citations?user=KfEtp4gAAAAJ&hl=en">Vladimir Pravosudov</a> and I program <a href="https://youtu.be/a69lKv65mZk?feature=shared">“smart” bird feeders</a> for an upcoming experiment.</p>
<p>I have spent the past six years <a href="https://scholar.google.com/citations?user=PBLRszkAAAAJ&hl=en">monitoring a population of mountain chickadees</a> here, tracking their life cycles and, importantly, their memory, working in a system <a href="https://chickadeecognition.com/">Pravosudov established in 2013</a>. The long, consistent record from this research site has allowed us to observe how chickadees survive in extreme winter snowfall and to identify ecological patterns and changes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/564534/original/file-20231208-19-4f18vw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A ring of tall, rectangular metal bird feeders mounded high with snow on top." src="https://images.theconversation.com/files/564534/original/file-20231208-19-4f18vw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564534/original/file-20231208-19-4f18vw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564534/original/file-20231208-19-4f18vw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564534/original/file-20231208-19-4f18vw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564534/original/file-20231208-19-4f18vw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564534/original/file-20231208-19-4f18vw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564534/original/file-20231208-19-4f18vw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=566&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Snow piles up on the experiment’s bird feeders. Each chickadee has a radio frequency identification tag that opens its assigned feeder, allowing scientists to track its movements and memory.</span>
<span class="attribution"><span class="source">Vladimir Pravosudov</span></span>
</figcaption>
</figure>
<p>In recent history, intense winters are often followed by drought years here in the Sierra Nevada and in much of <a href="https://doi.org/10.1038/s41598-021-95979-4">the U.S. West</a>. This teeter-totter pattern has been identified as one of the unexpected symptoms of climate change, and its impact on the chickadees is providing an early warning of the disruptions ahead for the dynamics within these coniferous forest ecosystems. </p>
<p>Our research shows that a mountain chickadee facing deep snow is, to borrow a cliche, like a canary in a coal mine – its survivability tells us about the challenges ahead.</p>
<figure class="align-center ">
<img alt="A chickadee sits on a man's finger as the two look at each other." src="https://images.theconversation.com/files/564900/original/file-20231211-17-53wkl2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564900/original/file-20231211-17-53wkl2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564900/original/file-20231211-17-53wkl2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564900/original/file-20231211-17-53wkl2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564900/original/file-20231211-17-53wkl2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564900/original/file-20231211-17-53wkl2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564900/original/file-20231211-17-53wkl2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The author, Benjamin Sonnenberg, and one of his research subjects − a young chickadee with a transponder tag on its leg.</span>
<span class="attribution"><span class="source">Benjamin Sonnenberg</span></span>
</figcaption>
</figure>
<h2>The extraordinary memory of a chickadee</h2>
<p>As Pravosudov calls out the next identification number, and as my legs slowly get colder and wetter, a charming and chipper “<a href="https://www.allaboutbirds.org/guide/Mountain_Chickadee/sounds#">DEE DEE DEE</a>” chimes down from a nearby tree. How is it that a bird weighing barely more than a few sheets of paper is more comfortable in this storm than I am?</p>
<p>The answer comes down to the chickadees’ incredible spatial cognitive abilities.</p>
<p>Cognition is the processes by which animals acquire, process, store and act on information from <a href="https://doi.org/10.1006/anbe.2000.1606">their environment</a>. It is critical to many species but is often subtle and difficult to measure in nonhuman animals.</p>
<p>Chickadees are food-storing specialists that hide tens of thousands of individual food items throughout the forest under edges of tree bark, or even between pine needles, each fall. Then, they use their specialized spatial memory to <a href="https://doi.org/10.1146/annurev-ecolsys-110512-135904">retrieve those food caches</a> in the months to come.</p>
<p>Conditions in the high Sierras can be harsh, and if chickadees can’t remember where their food is, they die.</p>
<p>We measure the spatial memory of chickadees using a classic associative learning task but in a very atypical <a href="https://doi.org/10.1016/j.anbehav.2015.10.015">location</a>. To do this, we hang a circular array of eight feeders equipped with radio-frequency identification and filled with seed in several locations across our <a href="https://doi.org/10.3389/fevo.2019.00257">field site</a>. Birds are tagged with “keys” – transponder tags in leg bands that contain individual identification numbers and allow them to open the doors of their assigned feeders to get a food reward.</p>
<p>The setup allows us to measure the spatial memory performance of individual chickadees, because they have to remember which feeder their key enables them to open. Over eight years, our findings demonstrate that chickadees with better spatial memory ability are <a href="https://doi.org/10.1016/j.cub.2019.01.006">more likely to survive</a> in the high mountains than those with worse memories. </p>
<p>However, chickadees may be facing increasing challenges that will shape their future in the high mountains. In 2017, a year with record-breaking snow levels, adult chickadees showed the lowest probability of survival <a href="https://doi.org/10.1007/s00265-020-2817-2">ever measured at our site</a>. This exceptionally extreme winter came with recurrent storms containing cold weather and high winds, making it difficult for even the memory savvy chickadees to forage and survive. </p>
<p>Nevertheless, triumphant populations have persisted in high-elevation mountain environments, but their future is becoming uncertain.</p>
<h2>What’s the problem?</h2>
<p>“It’s weather whiplash,” says <a href="https://scholar.google.com/citations?user=iEEye1UAAAAJ&hl=en">Adrian Harpold</a>, a mountain ecohydrologist. Harpold works to understand variations in climate patterns within forest environments, and one of his field sites lies alongside our chickadee research site. </p>
<p>The Sierra Nevada and other mountain ranges in western North America have been experiencing more <a href="https://statesummaries.ncics.org/chapter/ca/">extreme snow years and drought years</a>, amplified by climate change. Extreme snow linked to global warming might seem counterintuitive, but it’s basic physics. Warmer air can hold more moisture – <a href="https://climate.nasa.gov/explore/ask-nasa-climate/3143/steamy-relationships-how-atmospheric-water-vapor-amplifies-earths-greenhouse-effect/">about 7% more for every degree Celsius</a> (every 1.8 degrees Fahrenheit) that temperatures rise. This can result in heavier snowfall when storms strike.</p>
<p><iframe id="VfiF9" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/VfiF9/4/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>In 2023’s record winter, over 17 feet (5 meters) of snow covered the landscape that our chickadees were using every day. In fact, these intense storms and cold temperatures not only made it difficult for birds to survive the winter but made it almost impossible for them to breed the next summer: 46% of chickadee nests at our higher elevation site failed to produce any offspring. This was likely due to the deep snow that prevented them from finding emerging insects to feed nestlings or even reaching nesting sites at all until July.</p>
<h2>The cascading harms from too much snow</h2>
<p>Even in years of tremendous snowfall, chickadees can still use their finely honed spatial memories to recover food. However, severe storms can shorten their survival odds. And if they do survive the winter, their nesting sites – tree cavities – may be buried under feet of snow in the spring. </p>
<p>It doesn’t matter how smart you are if you can’t reach your nest.</p>
<p>Extreme snow oscillations also affect insects that are critical for feeding chickadee chicks. Limited resources lead to smaller chickadee offspring that are less likely to survive high in the mountains. </p>
<figure class="align-center ">
<img alt="A tiny baby chickadee sits in a man's hand. It's mouth below a still developing beak is bright yellow." src="https://images.theconversation.com/files/565552/original/file-20231213-15-r59z40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/565552/original/file-20231213-15-r59z40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/565552/original/file-20231213-15-r59z40.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/565552/original/file-20231213-15-r59z40.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/565552/original/file-20231213-15-r59z40.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/565552/original/file-20231213-15-r59z40.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/565552/original/file-20231213-15-r59z40.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Mountain chickadee chicks can struggle to survive during winters with extreme snow.</span>
<span class="attribution"><span class="source">Benjamin Sonnenberg</span></span>
</figcaption>
</figure>
<p>Snow cover is good for overwintering insects in most cases, as it provides an insulating blanket that saves them from dying during those freezing months. However, if the snow persists too long into the summer, insects can run out of energy and die before they can emerge, or emerge after chickadees <a href="https://doi.org/10.1111/brv.12105">really need them</a>. Drought years also can drive insect population decline. </p>
<p>Extremes at both ends of the spectrum are making it harder for chickadees to thrive, and more and more we are seeing oscillations between these extremes.</p>
<p>These compounded effects mean that in some years chickadees simply don’t successfully nest at all. This leads to a decline in chickadee populations in years with worse whiplash – drought followed by high snow on repeat – especially at high elevations. This is especially concerning, as many <a href="https://doi.org/10.1111/gcb.16187">mountain-dwelling avian species are forecasted to move up in elevation</a> to escape warming temperatures, which may turn out to be hazardous. </p>
<figure class="align-center ">
<img alt="Eight little chickadees in a circle in a wooden box, their tails all together in the center to keep their bodies warm." src="https://images.theconversation.com/files/564540/original/file-20231208-17-vwxtfo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564540/original/file-20231208-17-vwxtfo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=428&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564540/original/file-20231208-17-vwxtfo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=428&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564540/original/file-20231208-17-vwxtfo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=428&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564540/original/file-20231208-17-vwxtfo.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=538&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564540/original/file-20231208-17-vwxtfo.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=538&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564540/original/file-20231208-17-vwxtfo.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=538&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Baby chickadees stay warm inside a wooden box.</span>
<span class="attribution"><span class="source">Benjamin Sonnenberg</span></span>
</figcaption>
</figure>
<h2>Lessons for the future</h2>
<p>Chickadees may be portrayed as radiating tranquil beauty on holiday cards, but realistically, these loud, round ruffians are tough survivors of harsh winter environments in northern latitudes.</p>
<p>Our long-term research following these chickadees provides a unique window into the relationships between winter snow, chickadee populations and the biological community around them, such as <a href="https://link.springer.com/article/10.1007/s10584-007-9358-9">coniferous forests</a> and <a href="https://www.pnas.org/doi/abs/10.1073/pnas.2023989118">insect</a> populations. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/a69lKv65mZk?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Benjamin Sonnenberg and Vladimir Pravosudov show how the feeders work to test birds’ memories in a video about the early stages of their research.</span></figcaption>
</figure>
<p>These relationships illustrate that climate change is a more complicated story than just the temperature climb – and that its whiplash and cascading effects can destabilize ecosystems.</p><img src="https://counter.theconversation.com/content/217255/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Benjamin Sonnenberg receives funding from the National Science Foundation. </span></em></p>These tiny songbirds have extraordinary memories for the tens of thousands of spots where they hide food. But that doesn’t help when heavy snow blocks their access.Benjamin Sonnenberg, Ph.D. Candidate in Ecology, Evolution and Conservation Biology, University of Nevada, RenoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2188722023-12-12T18:01:46Z2023-12-12T18:01:46ZArctic Report Card 2023: From wildfires to melting sea ice, the warmest summer on record had cascading impacts across the Arctic<figure><img src="https://images.theconversation.com/files/564907/original/file-20231211-25-r8pwap.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5982%2C3988&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Giovanna Stevens grew up harvesting salmon at her family’s fish camp on Alaska's Yukon River. Climate change is interrupting hunting and fishing traditions in many areas.</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/aYukonRiverDisappearingSalmon/fa2665d81c31479a916a237985eec432/photo">AP Photo/Nathan Howard</a></span></figcaption></figure><p>The year 2023 shattered the record for the <a href="https://arctic.noaa.gov/report-card/report-card-2023/">warmest summer in the Arctic</a>, and people and ecosystems across the region felt the impact. </p>
<p>Wildfires forced evacuations <a href="https://earthobservatory.nasa.gov/images/151985/tracking-canadas-extreme-2023-fire-season">across Canada</a>. Greenland was so warm that a research station <a href="https://nsidc.org/ice-sheets-today/analyses/sudden-shift-southern-heat">at the ice sheet summit</a> recorded melting in late June, only its fifth melting event on record. <a href="https://climate.copernicus.eu/surface-air-temperature-august-2023">Sea surface temperatures</a> in the Barents, Kara, Laptev and Beaufort seas were 9 to 12 degrees Fahrenheit (5 to 7 degrees Celsius) above normal in August. </p>
<p>While reliable instrument measurements go back only to around 1900, it’s almost certain this was the Arctic’s hottest summer in centuries.</p>
<figure class="align-center ">
<img alt="A map shows Arctic temperatures in 2023 and a chart shows changing heat over time." src="https://images.theconversation.com/files/564698/original/file-20231210-27-qjqbgc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564698/original/file-20231210-27-qjqbgc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=891&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564698/original/file-20231210-27-qjqbgc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=891&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564698/original/file-20231210-27-qjqbgc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=891&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564698/original/file-20231210-27-qjqbgc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1120&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564698/original/file-20231210-27-qjqbgc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1120&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564698/original/file-20231210-27-qjqbgc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1120&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Summer heat extremes in 2023 and over time.</span>
<span class="attribution"><a class="source" href="https://arctic.noaa.gov/report-card/">NOAA, Arctic Report Card 2023</a></span>
</figcaption>
</figure>
<p>The year started out unusually wet, and snow accumulation during the winter of 2022-23 was above average across much the Arctic. But by May, high spring temperatures had left the <a href="https://arctic.noaa.gov/report-card/report-card-2023/terrestrial-snow-cover-2023/">North American snowpack at a record low</a>, exposing ground that quickly warmed and dried, fueling lightning-sparked fires across Canada.</p>
<p>In the <a href="https://arctic.noaa.gov/report-card/report-card-2023/">2023 Arctic Report Card</a>, released Dec. 12, we brought together 82 Arctic scientists from around the world to assess the Arctic’s vital signs, the changes underway and their effects on lives across the region and around the world.</p>
<h2>Heat’s cascading effects throughout the Arctic</h2>
<p>In an area as large as the Arctic, setting a new temperature record for a season by two-tenths of a degree Fahrenheit (0.1 degrees Celsius) of warming would be significant. Summer 2023 – July, August and September – <a href="https://arctic.noaa.gov/report-card/report-card-2023/">shattered the previous record</a>, set in 2016, by four times that. Temperatures almost everywhere in the Arctic were above normal.</p>
<p>A closer look at <a href="https://www.gov.nt.ca/en/newsroom/shane-thompson-historic-2023-wildfire-season">events in Canada’s Northwest Territories</a> shows how rising air temperature, sea ice decline and warming water temperature feed off one another in a warming climate.</p>
<figure class="align-center ">
<img alt="A map shows 2023 spring snow cover duration. A chart shows Arctic snow cover falling since the 1980s." src="https://images.theconversation.com/files/564696/original/file-20231210-23-a3z2r8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564696/original/file-20231210-23-a3z2r8.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1035&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564696/original/file-20231210-23-a3z2r8.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1035&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564696/original/file-20231210-23-a3z2r8.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1035&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564696/original/file-20231210-23-a3z2r8.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1300&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564696/original/file-20231210-23-a3z2r8.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1300&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564696/original/file-20231210-23-a3z2r8.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1300&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Arctic snow cover in 2023 and over time.</span>
<span class="attribution"><a class="source" href="https://arctic.noaa.gov/report-card/">NOAA, Arctic Report Card 2023</a></span>
</figcaption>
</figure>
<p>The <a href="https://arctic.noaa.gov/report-card/report-card-2023/">winter snow cover melted early</a> across large parts of northern Canada, providing an extra month for the Sun to heat up the exposed ground. The heat and lack of moisture dried out organic matter on and just below the surface; by November, <a href="https://cwfis.cfs.nrcan.gc.ca/report">70,000 square miles</a> (180,000 square kilometers) had burned across Canada, about a fifth of it in the Northwest Territories. </p>
<p>The very warm weather in May and June 2023 in the Northwest Territories also <a href="https://arctic.noaa.gov/report-card/report-card-2023/">heated up the mighty Mackenzie River</a>, which sent massive amounts of warm water into the Beaufort Sea to the north. The warm water melted the sea ice early, and currents also carried it west toward Alaska, where Mackenzie River water contributed to early sea ice loss along most of Northeast Alaska and to increased tundra vegetation growth.</p>
<figure class="align-center ">
<img alt="A map shows Arctic sea surface temperatures in 2023 and a chart shows temperatures rising over time." src="https://images.theconversation.com/files/564695/original/file-20231210-21-9359yk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564695/original/file-20231210-21-9359yk.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=1050&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564695/original/file-20231210-21-9359yk.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=1050&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564695/original/file-20231210-21-9359yk.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=1050&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564695/original/file-20231210-21-9359yk.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1320&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564695/original/file-20231210-21-9359yk.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1320&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564695/original/file-20231210-21-9359yk.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1320&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Sea surface temperatures have been rising.</span>
<span class="attribution"><a class="source" href="https://arctic.noaa.gov/report-card/">NOAA, Arctic Report Card 2023</a></span>
</figcaption>
</figure>
<p>Similar warmth in western Siberia also contributed to quickly melting sea ice and to high sea surface temperatures in the Kara and Laptev seas north of Russia. </p>
<p>The Arctic’s declining sea ice has been a big contributor to the <a href="https://doi.org/10.1016/j.gloplacha.2011.03.004">tremendous increase in average fall temperatures</a> across the region. Dark open water absorbs the sun’s rays during the summer and, in the autumn, acts as a heating pad, releasing heat back into the atmosphere. Even thin sea ice can greatly limit this heat transfer and allow dramatic cooling of air just above the surface, but the past 17 years have seen the <a href="https://climate.nasa.gov/vital-signs/arctic-sea-ice/">lowest sea ice extents</a> on record.</p>
<h2>Subsea permafrost: A wild card for climate</h2>
<p>The report includes <a href="https://arctic.noaa.gov/report-card/report-card-2023/">12 essays</a> exploring the effects of climate and ecosystem changes across the Arctic and how communities are adapting. One is a wake-up call about the risks in subsea permafrost, a potentially dangerous case of “out of sight, out of mind.”</p>
<p><a href="https://www.eurekalert.org/multimedia/672770">Subsea permafrost</a> is frozen soil in the ocean floor that is rich in organic matter. It has been gradually thawing since it was submerged after Northern Hemisphere ice sheets retreated thousands of years ago. Today, warmer ocean temperatures are <a href="https://arctic.noaa.gov/report-card/report-card-2023/">likely accelerating the thawing</a> of this hidden permafrost.</p>
<p>Just as with permafrost on land, when subsea permafrost thaws, the organic matter it contains decays and releases methane and carbon dioxide – greenhouse gases that contribute to global warming and worsen ocean acidification.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/564666/original/file-20231210-25-jz5ezj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A map shows most subsea permafrost off Siberia but also some off Alaska and Canada." src="https://images.theconversation.com/files/564666/original/file-20231210-25-jz5ezj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564666/original/file-20231210-25-jz5ezj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=425&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564666/original/file-20231210-25-jz5ezj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=425&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564666/original/file-20231210-25-jz5ezj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=425&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564666/original/file-20231210-25-jz5ezj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=534&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564666/original/file-20231210-25-jz5ezj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=534&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564666/original/file-20231210-25-jz5ezj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=534&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Known permafrost zones in the Northern Hemisphere. Greens are subsea permafrost.</span>
<span class="attribution"><a class="source" href="https://www.grida.no/resources/13519">GRID-Arendal/Nunataryuk</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>Scientists estimate that <a href="https://doi.org/10.1029/2018jc014675">nearly 1 million square miles</a> (2.5 million square kilometers) of subsea permafrost remains, but with little research outside the Beaufort Sea and Kara Sea, no one knows how soon it may release its greenhouse gases or how intense the warming effects will be.</p>
<h2>Salmon, reindeer and human lives</h2>
<p>For many people living in the Arctic, climate change is already disrupting lives and livelihoods.</p>
<p><a href="https://arctic.noaa.gov/report-card/report-card-2023/">Indigenous observers describe changes</a> in the sea ice that many people rely on for both subsistence hunting and coastal protection from storms. They have noted <a href="https://storymaps.arcgis.com/stories/30d30ab062ea4aadb39b3734dd7770ae">shifts in wind patterns</a> and increasingly intense ocean storms. On land, rising temperatures are making river ice less reliable for travel, and thawing permafrost is sinking roads and destabilizing homes.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/564028/original/file-20231206-29-r7k3zu.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A map with disasters and indicators of trouble in a warming Arctic." src="https://images.theconversation.com/files/564028/original/file-20231206-29-r7k3zu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564028/original/file-20231206-29-r7k3zu.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564028/original/file-20231206-29-r7k3zu.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564028/original/file-20231206-29-r7k3zu.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564028/original/file-20231206-29-r7k3zu.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564028/original/file-20231206-29-r7k3zu.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564028/original/file-20231206-29-r7k3zu.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Highlights from the Arctic Report Card 2023.</span>
<span class="attribution"><a class="source" href="https://arctic.noaa.gov/report-card/">NOAA, Arctic Report Card 2023</a></span>
</figcaption>
</figure>
<p>Obvious and dramatic changes are happening within human lifetimes, and they cut to the core of Indigenous cultures to the point that people are having to change how they put food on the table.</p>
<p>Western Alaska communities that rely on Chinook salmon saw another year of extreme low numbers of returning adult salmon in 2023, scarcity that disrupts both <a href="https://doi.org/10.5751/es-11972-260116">cultural practices and food security</a>. Yukon River Chinook have <a href="https://www.aykssi.org/wp-content/uploads/1615-AYK_SSI-EQ-Expert-Panel-Report-Illustrated-Summary-April-2020.pdf">decreased in size</a> by about 6% since the 1970s, and they’re producing fewer offspring. Then, in 2019, the year when many of this year’s returning Chinook salmon were born, exceptionally warm river water killed many of the young. </p>
<p>The returning Chinook salmon population has been so small during the past two years that <a href="https://www.adfg.alaska.gov/static/applications/dcfnewsrelease/1499128659.pdf">fisheries have been closed</a> even for subsistence harvest, which is the highest priority, in hopes that the salmon population recovers.</p>
<p>The <a href="https://doi.org/10.1088/1748-9326/ac1a36">inability to fish, or to hunt</a> seals because the sea ice has thinned, is not just a food issue. Time spent at fish camps is <a href="https://arctic.noaa.gov/report-card/report-card-2021/the-impact-of-covid-19-on-food-access-for-alaska-natives-in-2020/">critical for many Alaska Indigenous cultures</a> and traditions, and kids are increasingly missing out on that experience. </p>
<p>As Indigenous communities adapt to ecosystem changes, people are also working to heal their landscapes.</p>
<figure class="align-center ">
<img alt="A man in colorful jacket and hat stands surrounded by dozens of reindeer." src="https://images.theconversation.com/files/564916/original/file-20231211-21-nsrchx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/564916/original/file-20231211-21-nsrchx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=394&fit=crop&dpr=1 600w, https://images.theconversation.com/files/564916/original/file-20231211-21-nsrchx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=394&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/564916/original/file-20231211-21-nsrchx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=394&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/564916/original/file-20231211-21-nsrchx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=496&fit=crop&dpr=1 754w, https://images.theconversation.com/files/564916/original/file-20231211-21-nsrchx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=496&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/564916/original/file-20231211-21-nsrchx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=496&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A Sámi reindeer herder in traditional clothes counts new calves while preparing the herd for the arduous winter months.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/sami-reindeer-herder-in-traditional-brightly-coloured-news-photo/535053696">In Pictures Ltd./Corbis via Getty Images</a></span>
</figcaption>
</figure>
<p>In Finland, an <a href="https://arctic.noaa.gov/report-card/report-card-2023/peatlands-and-associated-boreal-forests-of-finland-under-restoration/">effort to restore damaged reindeer habitat</a> in collaboration with Sámi reindeer herders is helping to preserve their way of life. For many decades, commercial logging was allowed to tear up hundreds to thousands of square miles of reindeer peatland habitat. </p>
<p><a href="https://youtu.be/w_DUAzQMH_w?feature=shared">The Sámi</a> and their partners are working to replant turf and rewild 125,000 acres (52,000 hectares) of peatlands for reindeer grazing. Degraded peatlands <a href="https://doi.org/10.1038/s43247-022-00547-x">also release greenhouse gases</a>, contributing to climate change. Keeping them healthy helps capture and store carbon away from the atmosphere.</p>
<p>Temperatures in the Arctic have been rising <a href="https://doi.org/10.1038/s43247-022-00498-3">more than three times faster</a> than the global average, so it’s not surprising that the Arctic saw its warmest summer and sixth warmest year on record. The 2023 Arctic Report Card is a reminder of what’s a stake, both the risks as the planet warms and the lives and cultures already being disrupted by climate change.</p><img src="https://counter.theconversation.com/content/218872/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rick Thoman receives funding from the National Oceanic and Atmospheric Administration (NOAA) for serving as an editor for the Arctic Report Card.</span></em></p><p class="fine-print"><em><span>Matthew L. Druckenmiller receives funding from the National Oceanic and Atmospheric Administration (NOAA) for serving as an editor for the Arctic Report Card.</span></em></p><p class="fine-print"><em><span>Twila A. Moon receives funding from the National Oceanic and Atmospheric Administration (NOAA) for serving as an editor for the Arctic Report Card.</span></em></p>The early heat melted snow and warmed rivers, heating up the land and downstream ocean areas. The effects harmed salmon fisheries, melted sea ice and fueled widespread fires.Rick Thoman, Alaska Climate Specialist, University of Alaska FairbanksMatthew L. Druckenmiller, Research Scientist, National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado BoulderTwila A. Moon, Deputy Lead Scientist, National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2153952023-10-12T12:30:45Z2023-10-12T12:30:45ZWhat is a strong El Niño? Meteorologists anticipate a big impact in winter 2023-2024, but the forecasts don’t all agree<figure><img src="https://images.theconversation.com/files/553361/original/file-20231011-29-363wak.png?ixlib=rb-1.1.0&rect=32%2C873%2C3211%2C2058&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The El Niño pattern stands out in the warm sea surface temperature anomalies in the Pacific in 2023</span> <span class="attribution"><a class="source" href="https://www.climate.gov/maps-data/data-snapshots/data-source/sst-enso-region-monthly-difference-average">NOAA Climate.gov</a></span></figcaption></figure><p><em>Meteorologists have been talking for weeks about <a href="https://www.accuweather.com/en/winter-weather/us-winter-forecast-for-the-2023-2024-season/1583853">a snowy season ahead</a> in the southern Rockies and the Sierra Nevada. They anticipate <a href="https://www.powder.com/trending-news/el-nino-huge-snow-east">more storms</a> in the U.S. South and Northeast, and warmer, drier conditions across the already dry Pacific Northwest and the upper Midwest.</em></p>
<p><em>One phrase comes up repeatedly with these projections: <a href="https://www.wcpo.com/weather/weather-101/a-strong-el-nino-expected-this-winter-heres-what-that-means-for-our-weather">a strong El Niño</a> is coming.</em></p>
<p><em>It sounds ominous. But what does that actually mean? We asked <a href="https://scholar.google.com/citations?user=z7CXcXkAAAAJ&hl=en">Aaron Levine</a>, an atmospheric scientist at the University of Washington whose research focuses on El Niño.</em></p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/wVlfyhs64IY?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">NOAA explains in animations how El Niño forms.</span></figcaption>
</figure>
<h2>What is a strong El Niño?</h2>
<p>During a normal year, the warmest sea surface temperatures are in the western Pacific and the Indian Ocean, in what’s known as the <a href="https://doi.org/10.1186/s40562-016-0054-3">Indo-Western Pacific warm pool</a>.</p>
<p>But every few years, the trade winds that blow from east to west weaken, allowing that warm water to slosh eastward and <a href="https://www.pmel.noaa.gov/elnino/schematic-diagrams">pile up along the equator</a>. The warm water causes the air above it to warm and rise, fueling precipitation in the central Pacific and shifting atmospheric circulation patterns across the basin.</p>
<p>This pattern is <a href="https://www.pmel.noaa.gov/elnino/what-is-el-nino">known as El Niño</a>, and it can <a href="https://www.climate.gov/media/13628">affect weather around the world</a>.</p>
<figure class="align-center ">
<img alt="An animation shows how warm water builds up along the equator off South America. The box where temperatures are measured is south of Hawaii." src="https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=272&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=272&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=272&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=342&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=342&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553048/original/file-20231010-23-c36xip.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=342&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The box shows the Niño 3.4 region as El Niño begins to develop in the tropical Pacific, from January to June 2023.</span>
<span class="attribution"><a class="source" href="https://www.climate.gov/">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>A strong El Niño, in the most basic definition, occurs once the average sea surface temperature in the equatorial Pacific is at least 1.5 degrees Celsius (2.7 Fahrenheit) warmer than normal. It’s measured in an imaginary box along the equator, roughly south of Hawaii, known as the <a href="https://svs.gsfc.nasa.gov/4695">Nino 3.4 Index</a>.</p>
<p>But El Niño is a coupled ocean-atmosphere phenomenon, and the atmosphere also plays a crucial role.</p>
<p>What has been surprising about this year’s El Niño – and still is – is that the atmosphere hasn’t responded as much as we would have expected based on the rising sea surface temperatures.</p>
<h2>Is that why El Niño didn’t affect the 2023 hurricane season the way forecasts expected?</h2>
<p>The 2023 Atlantic hurricane season is a good example. Forecasters often use El Niño as a predictor of <a href="https://www.weather.gov/ilx/swop-springtopics">wind shear</a>, which can tear apart Atlantic hurricanes. But with the atmosphere not responding to the warmer water right away, the impact on Atlantic hurricanes was lessened and it turned out to be a <a href="https://www.nytimes.com/article/tropical-storm-sean-hurricane.html">busy season</a>.</p>
<p><a href="https://doi.org/10.1175/JCLI-D-12-00097.1">The atmosphere is what transmits El Niño’s impact</a>. Heat from the warm ocean water causes the air above it to warm and rise, which fuels precipitation. That air sinks again over cooler water. </p>
<p>The rising and sinking creates giant loops in the atmosphere <a href="https://www.climate.gov/news-features/blogs/enso/walker-circulation-ensos-atmospheric-buddy">called the Walker Circulation</a>. When the warm pool’s water shifts eastward, that also shifts where the rising and sinking motions happen. The atmosphere reacts to this change like ripples in a pond when you throw a stone in. These ripples affect the jet stream, which steers weather patterns in the U.S.</p>
<p>This year, in comparison with other large El Niño events – such as <a href="https://www.climate.gov/news-features/blogs/enso/united-states-el-ni%C3%B1o-impacts-0">1982-83, 1997-98</a> and <a href="https://www.climate.gov/news-features/understanding-climate/2015-state-climate-el-ni%C3%B1o-came-saw-and-conquered">2015-16</a> – we’re not seeing the same change in where the precipitation is happening. It’s taking much longer to develop, and it’s not as strong.</p>
<p>Part of that, presumably, is related to the whole tropics being very, very warm. But <a href="https://doi.org/10.1029/2019GL086182">this is still an emerging field of research</a>.</p>
<p>How El Niño will change with global warming is a big and open question. El Niño <a href="https://www.climate.gov/news-features/understanding-climate/climate-variability-oceanic-nino-index">only happens every few years</a>, and there’s a fair amount of variability between events, so just getting a baseline is tough.</p>
<h2>What does a strong El Niño typically mean for US weather?</h2>
<p>During <a href="https://www.climate.gov/enso">a typical El Niño winter</a>, the U.S. South and Southwest are cooler and wetter, and the Northwest is warmer and drier. The upper Midwest tends to be drier, while the Northeast tends to be a little wetter. </p>
<p>The likelihood and the intensity generally scale with the strength of the El Niño event.</p>
<p>El Niño has traditionally been good for the mountain snowpack in California, which the state relies for a large percentage of its water. But it is often not so good for the Pacific Northwest snowpack.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Two maps showing wetter, cooler weather in the Southeast and drier warmer air in the north during El Nino." src="https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=834&fit=crop&dpr=1 600w, https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=834&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=834&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1047&fit=crop&dpr=1 754w, https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1047&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/553424/original/file-20231012-15-3wfvdw.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1047&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">The jet stream takes a very different path in a typical El Niño vs. La Niña winter weather pattern. But these patterns have a great deal of variability. Not every El Niño or La Niña year is the same.</span>
<span class="attribution"><a class="source" href="https://www.climate.gov/media/14484">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>The <a href="https://www.climate.gov/news-features/featured-images/how-el-ni%C3%B1o-and-la-ni%C3%B1a-affect-winter-jet-stream-and-us-climate">jet stream plays a role</a> in that shift. When the polar jet stream is either displaced very far northward or southward, storms that would normally move through Washington or British Columbia are steered to California and Oregon instead.</p>
<h2>What do the forecasts show for the months ahead?</h2>
<p>Whether forecasters think a strong El Niño will develop depends on whose forecast model they trust.</p>
<p>This past spring, the <a href="https://www.weather.gov/media/climateservices/NWS%20Climate%20Forecast%20and%20Tools.pdf">dynamical forecast models</a> were <a href="https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-sst_table">already very confident</a> about the potential for a strong El Niño developing. These are big models that solve basic physics equations, starting with current oceanic and atmospheric conditions. </p>
<p>However, statistical models, which use statistical predictors of El Niño calculated from historical observations, were less certain.</p>
<p>Even in the <a href="https://iri.columbia.edu/our-expertise/climate/forecasts/enso/current/?enso_tab=enso-sst_table">most recent forecast model outlook</a>, the dynamical forecast models were predicting a stronger El Niño than the statistical models were.</p>
<p>If you go by just a sea surface temperature-based El Niño index, the forecast is for a fairly strong El Niño. </p>
<p>But the indices that incorporate the atmosphere are not responding in the same way. We’ve seen <a href="https://psl.noaa.gov/enso/enso.current.html">atmospheric anomalies</a> – as measured by cloud height monitored by satellites or sea-level pressure at monitoring stations – on and off in the Pacific since May and June, <a href="https://images.theconversation.com/files/553327/original/file-20231011-15-kprvx9.png">but not in a very robust fashion</a>. Even in September, they were nowhere near as large as they were in 1982, in terms of overall magnitude.</p>
<p>We’ll see if the atmosphere catches up by wintertime, when El Niño peaks.</p>
<h2>How long do El Niños last?</h2>
<p>Often during El Niño events – particularly strong El Niño events – the sea surface temperature anomalies collapse really quickly during the Northern Hemisphere spring. Almost all end in April or May.</p>
<p>One reason is that El Niño sows the seeds of its own demise. When El Niño happens, it <a href="https://doi.org/10.1175/1520-0469(1997)054%3C0811:AEORPF%3E2.0.CO;2">uses up that warm water</a> and the warm water volume shrinks. <a href="https://doi.org/10.1175/1520-0442(2000)013%3C3551:OOWWVC%3E2.0.CO;2">Eventually, it has eroded its fuel</a>.</p>
<p><iframe id="aOiS8" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/aOiS8/14/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>The surface can stay warm for a while, but once the heat from the subsurface is gone and the trade winds return, the El Niño event collapses. At the end of past El Niño events, the sea surface anomaly dropped very fast and we saw conditions typically switch to La Niña – El Niño’s cooler opposite.</p><img src="https://counter.theconversation.com/content/215395/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Aaron Levine receives funding from NOAA and has received funding in the past from the National Research Council. He is a member of the American Geophysical Union </span></em></p>An atmospheric scientist explains how El Niño works, this year’s oddities and why this phenomenon doesn’t last long.Aaron Levine, Atmospheric Research Scientist, CICOES, University of WashingtonLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2146192023-10-04T16:40:14Z2023-10-04T16:40:14ZUnderstanding the dynamics of snow cover in forests can help us predict flood risks<figure><img src="https://images.theconversation.com/files/551050/original/file-20230926-17-3adew2.jpg?ixlib=rb-1.1.0&rect=23%2C5%2C3914%2C2964&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A better understanding of the interactions between snow cover and forest will help improve hydrological models and thus ensure public protection against flooding.</span> <span class="attribution"><span class="source">(Benjamin Bouchard)</span>, <span class="license">Fourni par l'auteur</span></span></figcaption></figure><p>For more than six months a year, Quebec’s boreal forest is covered in a thick blanket of snow. While this is essential for the balance of our ecosystems, for the people living downstream from forested watersheds the snow can be like a sword of Damocles hanging over their heads. </p>
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<figure class="align-right ">
<img alt="" src="https://images.theconversation.com/files/524152/original/file-20230503-20-rp105s.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/524152/original/file-20230503-20-rp105s.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524152/original/file-20230503-20-rp105s.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524152/original/file-20230503-20-rp105s.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524152/original/file-20230503-20-rp105s.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524152/original/file-20230503-20-rp105s.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524152/original/file-20230503-20-rp105s.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=754&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<p><strong>This article is part of <em>La Conversation Canada’s</em> series <a href="https://theconversation.com/ca-fr/topics/foret-boreale-138017">The boreal forest: A thousand secrets, a thousand dangers</a></strong></p>
<p><br><em>La Conversation Canada invites you to take a virtual walk in the heart of the boreal forest. In this series, our experts focus on management and sustainable development issues, natural disturbances, the ecology of terrestrial wildlife and aquatic ecosystems, northern agriculture and the cultural and economic importance of the boreal forest for Indigenous peoples. We hope you have a pleasant — and informative — walk through the forest!</em></p>
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<p>The major floods of spring 2023 in the Charlevoix region show why the snow cover poses a risk. </p>
<p>Last winter, the Rivière du Gouffre watershed, of which <a href="https://charlevoixmontmorency.ca/l-obv-cm/territoire/">nearly 75 per cent is covered by forests</a>, accumulated a large amount of snow. The melting of this snow cover combined with an extremely intense rainfall event helped push the river out of its bed, causing <a href="https://www.cbc.ca/news/canada/montreal/flood-baie-saint-paul-residents-cleaning-1.6829490">unprecedented flooding in Baie-Saint-Paul</a>.</p>
<p>As part of my PhD at Université Laval, in collaboration with <a href="https://sentinellenord.ulaval.ca/en/home">Sentinel North</a>, I am looking at the impact of snow cover properties on watershed hydrology in the boreal forest.</p>
<h2>Rain as an energy carrier</h2>
<p>As we saw in the spring of 2023, rain events combined with snow cover can lead to a sudden rise in river water levels. One reason for this is that rainwater transfers heat to the snow. </p>
<p>A heat exchange occurs between rain and snow when their temperatures differ. The snow warms up, and the rain cools down. Once the snow has reached a temperature of 0°C, any additional heat from the rain causes melting.</p>
<p>So, a snow cover of near 0 C, common in spring, and heavy rainfall at high temperatures, together create conditions where both meltwater and rainwater contribute to a higher flow of water. This increases the likelihood of flooding. However, this will only happen if the water produced can flow easily through the snow cover. </p>
<p>On the other hand, a cold snow cover combined with low-temperature rainfall can lead to rainwater freezing in the snow. This water will then remain trapped in the snow and won’t present a flooding risk. </p>
<p>After all, heat exchange goes both ways!</p>
<h2>The snow cover, a complexly structured environment</h2>
<p>The snow cover is a porous medium that does not have uniform physical properties. Rather, it is a stack of snow layers that represent the history of the winter’s meteorological events. Rainwater must percolate through all the snow layers to reach the ground, and eventually, the watercourse.</p>
<p>Some layers, such as fine-grained layers and layers of ice, limit the flow of water through the snow. In contrast, coarse-grained layers, which have larger pores, facilitate the flow of water. As a result, they enable rainwater and meltwater to reach the ground quickly.</p>
<h2>The role of the forest</h2>
<p>The structure of the snow cover influences the risk of flooding. But what effect do forests have on snow structure? </p>
<p>By intercepting part of the precipitation in its solid form (snow), trees limit the accumulation of snow on the ground. That, in turn, contributes to the <a href="https://doi.org/10.1029/JC088iC09p05475">growth of snow grains and pores on the ground</a> through upward water vapour flux. In addition, the discharge of snow intercepted by trees in solid or liquid form <a href="https://doi.org/10.1016/j.foreco.2019.01.052">increases the heterogeneity of the snow cover</a>. These processes promote rapid water flow in the snow cover that forms beneath the trees.</p>
<h2>The same everywhere?</h2>
<p>Forest cover is far from uniform in the boreal forest. It’s more akin to sparse vegetation with treeless zones known as gaps. In these gaps, the structure of the snow cover is very different from that under the trees.</p>
<p>The greater accumulation of snow in the gaps favours the compaction of snow layers and the formation of fine grains. In addition, daily cycles of surface refreezing lead to the formation of low-permeability ice layers. </p>
<p>The snow cover in the gaps is, therefore, less favourable to the percolation of water to the ground <a href="https://doi.org/10.1002/hyp.14681">than that found under the trees</a>.</p>
<p>But does this mean that the presence of gaps reduces the risk of flooding? Not quite.</p>
<h2>Snow melts faster in gaps</h2>
<p>The structure of the snow cover is just one of the factors that influences flooding. Ground that is frozen, which limits infiltration, as well as rapid snowmelt also increase the risk of flooding. </p>
<p>In Québec’s boreal forests, although the ground does not freeze in the gaps between trees due to the insulating nature of the snow cover, the <a href="https://doi.org/10.5194/hess-2023-191">melt rate is much higher</a> because solar radiation is stronger than it is under the trees, particularly in spring. </p>
<p>Although more snow would accumulate in the gaps, it takes less time to melt and reaches the watercourse more quickly than the snow under the trees. That increases waterflow and, as a consequence, the risk of flooding.</p>
<p>The combination of thicker snow cover in the gaps and more permeable snow layers under the trees contributed to the Rivière du Gouffre flooding Baie-Saint-Paul during the extreme rainfall of spring 2023.</p>
<p>Rainfall events like this <a href="https://www.ouranos.ca/en/precipitations-projected-changes">will continue to increase in frequency as global temperatures warm</a>. However, increased knowledge of the interactions between snow cover and forest will help improve hydrological models and ensure better public protection against flooding.</p><img src="https://counter.theconversation.com/content/214619/count.gif" alt="La Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Benjamin Bouchard has received funding from the Fonds de recherche Nature et technologie du Québec (FRQNT), the Natural Sciences and Engineering Research Council of Canada (NSERC) and Sentinel North. </span></em></p><p class="fine-print"><em><span>Daniel Nadeau has received funding from Environment and Climate Change Canada, as well as from the Natural Sciences and Engineering Research Council of Canada.</span></em></p><p class="fine-print"><em><span>Florent Domine has received funding from the Natural Sciences and Engineering Research Council of Canada.</span></em></p>A better understanding of the interactions between the boreal forest and snow will make it possible to improve hydrological models and ensure optimal management of the resource.Benjamin Bouchard, Étudiant-chercheur au doctorat en génie des eaux, Université LavalDaniel Nadeau, Professeur titulaire en hydrologie des régions froides, Université LavalFlorent Domine, Professeur, chimie, Université LavalLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2049752023-05-04T14:25:46Z2023-05-04T14:25:46ZCloud seeding can increase rain and snow, and new techniques may make it a lot more effective – podcast<figure><img src="https://images.theconversation.com/files/524204/original/file-20230503-19-bx8o26.jpg?ixlib=rb-1.1.0&rect=418%2C594%2C6930%2C4308&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Cloud seeding can increase rainfall and reduce hail damage to crops, but its use is limited.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/colorado-supercell-royalty-free-image/1303884216?phrase=Rain+storm&adppopup=true">John Finney Photography/Moment via Getty Images</a></span></figcaption></figure><p>When an unexpected rainstorm leaves you soaking wet, it is an annoyance. When a drought leads to fires, crop failures and water shortages, the significance of weather becomes vitally important.</p>
<p>If you could control the weather, would you?</p>
<p>Small amounts of rain can mean the difference between struggle and success. For <a href="https://climateviewer.com/2014/03/25/history-cloud-seeding-pluviculture-hurricane-hacking/">nearly 80 years</a>, an approach called cloud seeding has, in theory, given people the ability to get more rain and snow from storms and make hailstorms less severe. But only recently have scientists been able to peer into clouds and begin to understand how effective cloud seeding really is.</p>
<p>In this episode of “The Conversation Weekly,” we speak with three researchers about the simple yet murky science of cloud seeding, the economic effects it can have on agriculture, and research that may allow governments to use cloud seeding in more places.</p>
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<p><a href="https://scholar.google.com/citations?user=BSQl42wAAAAJ&hl=en&oi=ao">Katja Friedrich</a>, a professor of atmospheric and oceanic sciences at the University of Colorado, Boulder in the U.S., is a leading researcher on cloud seeding. “When we do cloud seeding, we are looking for clouds that have tiny super-cooled liquid droplets,” she explains. Silver iodide is very similar in structure to an ice crystal. When the droplets touch a particle of silver iodide, “they freeze, then they can start merging with other ice crystals, become snowflakes and fall out of the cloud.”</p>
<p>While the process is fairly straightforward, measuring how effective it is in the real world is not, according to Friedrich. “The problem is that once we modify a cloud, it’s really difficult to say what would’ve happened if you hadn’t cloud-seeded.” It’s hard enough to predict weather without messing with it artificially. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A plane wing with a cylindrical device attached." src="https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=370&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=370&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=370&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=465&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=465&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=465&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Cloud seeding is usually done by planes equipped with devices – like the one attached to the wing of this plane – that spray silver iodide into the atmosphere.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Cloud_seeding#/media/File:Hagelflieger-EDTD.jpg">Zuckerle/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>In 2017, Friedrich’s research group had a breakthrough in measuring the effect of cloud seeding. “We flew some aircraft, released silver iodide and generated these clouds that were like these six exact lines that were downstream of where the aircraft were seeding,” she says. They then had a second aircraft fly through the clouds. “We could actually <a href="https://doi.org/10.1073/pnas.1716995115">quantify how much snow we could produce</a> by two hours of cloud seeding.” That effect, according to research on cloud seeding, is an increase in precipitation of somewhere around 5% to 20% or 30%, depending on conditions.</p>
<p>Measuring the effect on precipitation – whether rain or snow – directly may have taken complex science and a bit of luck, but in places that have been using cloud seeding for long periods of time, the economic benefits are shockingly clear. </p>
<p><a href="https://www.ndsu.edu/agriculture/ag-home/directory/dean-bangsund">Dean Bangsund</a> is a researcher at North Dakota State University who studies the economics of agriculture. “We have a high amount of hail damage in North Dakota,” said Bangsund. For decades, the state government has been using cloud seeding to reduce hail damage, as cloud seeding leads to the formation of more pieces of smaller hail compared to fewer pieces of larger hail. “It doesn’t 100% eliminate hail; it’s designed to soften the impact.”</p>
<p>Every 10 years, the state of North Dakota does an <a href="https://www.cabdirect.org/cabdirect/abstract/20193399635">analysis on the economic impacts of the cloud seeding</a> program, measuring both reduction in hail damage and benefits from increased rain. Bangsund led the last report and says that for every dollar spent on the cloud seeding program, “we are looking at something that is anywhere from $8 or $9 in benefit on the really lowest scale, up to probably $20 of impact per acre.” With millions of acres of agricultural fields in the cloud seeding area, that is a massive economic benefit.</p>
<p>Both Freidrich and Bangsund emphasized that cloud seeding, while effective in some cases, cannot be used everywhere. There is also a lot of uncertainty in how much of an effect it has. One way to improve the effectiveness and applicability of cloud seeding is by improving the seed. <a href="https://scholar.google.com/citations?view_op=list_works&hl=en&hl=en&user=OxrNpiEAAAAJ&sortby=pubdate">Linda Zou</a> is a professor of civil infrastructure and environmental engineering at Khalifa University in the United Arab Emirates. </p>
<p>Her work has focused on developing a replacement for silver iodide, and her lab has <a href="https://www.technologyreview.com/2022/03/28/1048275/scientists-advance-cloud-seeding-capabilities-with-nanotechnology/">developed what she calls a nanopowder</a>. “I start with table salt, which is sodium chloride,” says Zou. “This desirable-sized crystal is then coated with a thin nanomaterial layer of titanium dioxide.” When salt gets wet, it melts and forms a droplet that can efficiently merge with other droplets and fall from a cloud. Titanium dioxide attracts water. Put the two together and you get a very effective cloud-seeding material. </p>
<p>From indoor experiments, Zou found that “with the nanopowders, there are 2.9 times the formation of larger-size water droplets.” These nanopowders can also form ice crystals at warmer temperatures and less humidity than silver iodide. </p>
<p>As Zou says, “if the material you are releasing is more reactive and can work in a much wider range of conditions, that means no matter when you decide to use it, the chance of success will be greater.”</p>
<hr>
<p>This episode was written and produced by Katie Flood. Mend Mariwany is the executive producer of The Conversation Weekly. Eloise Stevens does our sound design, and our theme music is by Neeta Sarl.</p>
<p>You can find us on Twitter <a href="https://twitter.com/TC_Audio">@TC_Audio</a>, on Instagram at <a href="https://www.instagram.com/theconversationdotcom/">theconversationdotcom</a> or <a href="mailto:podcast@theconversation.com">via email</a>. You can also subscribe to The Conversation’s <a href="https://theconversation.com/newsletter">free daily email here</a>. </p>
<p>Listen to “The Conversation Weekly” via any of the apps listed above, download it directly via our <a href="https://feeds.acast.com/public/shows/60087127b9687759d637bade">RSS feed</a> or find out <a href="https://theconversation.com/how-to-listen-to-the-conversations-podcasts-154131">how else to listen here</a>.</p>
<hr><img src="https://counter.theconversation.com/content/204975/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>None of the interviewees work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p><p class="fine-print"><em><span> </span></em></p>Cloud seeding – spraying materials into clouds to increase precipitation – has been around for nearly 80 years. But only recently have scientists been able to measure how effective it really is.Daniel Merino, Associate Science Editor & Co-Host of The Conversation Weekly Podcast, The ConversationNehal El-Hadi, Science + Technology Editor & Co-Host of The Conversation Weekly Podcast, The ConversationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2038742023-04-17T12:43:14Z2023-04-17T12:43:14ZEpic snow from all those atmospheric rivers in the West is starting to melt, and the flood danger is rising<figure><img src="https://images.theconversation.com/files/521225/original/file-20230417-20-d354fm.jpeg?ixlib=rb-1.1.0&rect=0%2C2%2C1917%2C1336&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Tulare Lake is reemerging as flood water spreads across miles of California farmland.
</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/agribusiness-consultant-mark-grewel-stands-on-a-farm-road-news-photo/1249529651">Luis Sinco / Los Angeles Times via Getty Images</a></span></figcaption></figure><p><em>To get a sense of the enormous amount of water atmospheric rivers dumped on the Western U.S. this year and the magnitude of the flood risk ahead, take a look at California’s Central Valley, where about <a href="https://ca.water.usgs.gov/projects/central-valley/about-central-valley.html">a quarter of the nation’s food</a> is grown.</em></p>
<p><em>This region was once home to the largest freshwater lake west of the Rockies. But the rivers that fed Tulare Lake were <a href="https://sarahamooneymuseum.org/a-look-back/tulare-lake-was-once-considered-largest-body-of-water-west-of-mississippi/">dammed and diverted</a> long ago, leaving it nearly dry by 1920. Farmers have been growing food on the fertile lake bed for decades.</em></p>
<p><em>This year, however, <a href="https://earthobservatory.nasa.gov/images/151174/return-of-tulare-lake">Tulare Lake is remerging</a>. Runoff and snowmelt from the Sierra Nevada have overwhelmed waterways and flooded farms and orchards. After similar storms in 1983, the lake covered <a href="https://www.upi.com/Archives/1983/05/30/The-massive-wall-of-debris-laden-water-that-roared-down/9734423115200/">more than 100 square miles</a>, and scientists say this year’s precipitation is looking a lot like 1983. Communities there and across the West are preparing for flooding and mudslide disasters as <a href="https://www.drought.gov/drought-status-updates/snow-drought-current-conditions-and-impacts-west-2023-04-06">record snow</a> begins to melt.</em></p>
<figure class="align-center ">
<img alt="Satellite images show farmland with only a few small lakes in early March, then a larger lake covering that farmland by early April." src="https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=437&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=437&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=437&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=549&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=549&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521150/original/file-20230416-28-gpz5lm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=549&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Tulare Lake, long dry, begins to reemerge in March 2023 as flood water spreads across farm fields.</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/images/151174/return-of-tulare-lake">NASA Earth Observatory</a></span>
</figcaption>
</figure>
<p><em>We asked Chad Hecht, a meteorologist with the Center for Western Weather and Water Extremes at the University of California San Diego’s Scripps Institution of Oceanography, how 2023’s storms compare to past extremes and what to expect in the future.</em></p>
<h2>How extreme were this year’s atmospheric rivers?</h2>
<p>California averages about 44 atmospheric rivers a year, but typically, only about six of them are strong storms that contribute most of the annual precipitation total and cause the kind of flooding we’ve seen this year.</p>
<p>This year, in a three-week window from about Dec. 27, 2022, to Jan. 17, 2023, we saw nine atmospheric rivers make landfall, five of them <a href="https://doi.org/10.1029/2022JD037180">categorized as strong</a> or greater magnitude. That’s how active it’s been, and that was only the beginning.</p>
<figure class="align-center ">
<img alt="Map of where atmospheric rivers arrived through the end of March 2023" src="https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=540&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=540&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521092/original/file-20230414-26-gufn23.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=540&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Where atmospheric rivers hit during the first half of the 2023 water year, which started Oct. 1. The arrows show where the storms were strongest, but their impact reached far wider.</span>
<span class="attribution"><a class="source" href="https://cw3e.ucsd.edu/">Center For Western Weather and Water Extremes, Scripps Institution of Oceanography</a></span>
</figcaption>
</figure>
<p>In all, the state experienced 31 atmospheric rivers through the end of March: one extreme, six strong, 13 moderate and 11 weak. And other storms in between gave the Southern Sierra one of its wettest Marches on record. </p>
<p>These storms don’t just affect California. Their <a href="https://www.nrcs.usda.gov/wps/portal/wcc/home/quicklinks/imap">precipitation</a> has pushed the snow-water equivalent levels <a href="https://www.nrcs.usda.gov/wps/portal/wcc/home/quicklinks/imap">well above average across much of the West</a>, including in Oregon, Nevada, Utah, Idaho and the mountains of western Colorado, Arizona and New Mexico.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=726&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=726&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=726&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=912&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=912&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521152/original/file-20230416-28-zyyvgq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=912&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Snow water equivalent is a measure of the water in snowpack. Many basins across the West were well over 200% of average in 2023.</span>
<span class="attribution"><a class="source" href="https://www.nrcs.usda.gov/wps/portal/wcc/home/quicklinks/imap">NRCS/USDA</a></span>
</figcaption>
</figure>
<p>In terms of records, the big numbers this year were in California’s Southern Sierra Nevada. The region has had 11 moderate atmospheric rivers – double the average of 5.5 – and an additional four strong ones. </p>
<p>Overall, California has about <a href="https://cdec.water.ca.gov/reportapp/javareports?name=PLOT_SWC.pdf">double its normal snowpack</a>, and some locations have experienced more than double the number of strong atmospheric rivers it typically sees. The result is that Northern Sierra snow water content is 197% of normal. The central region is 238% of normal, and the Southern Sierra is 296% of normal.</p>
<h2>What risks does all that snow in the mountains create?</h2>
<p>There is <a href="https://www.kcra.com/article/tahoe-ski-resorts-extend-season-snow-palisades/43403916">a lot of snow</a> in the Sierra Nevada, and it is going to come off the mountains at some point. It’s possible we are going to be looking at snowmelt into late June or July in California, and that’s far into summer for here.</p>
<p>Flooding is certainly a possibility. The closest year for comparison in terms of the amount of snow would be 1983, when the average statewide snow water content was 60.3 inches in May. That was a <a href="https://www.pressdemocrat.com/article/news/photos-a-look-back-at-the-1983-floods">rough year</a>, with <a href="https://www.washingtonpost.com/archive/politics/1983/06/01/rain-melting-snow-continue-to-menace-states-in-the-west/4aa62a9a-ce91-46f7-a579-607c4843a318/">flooding and mudslides</a> in <a href="https://www.sltrib.com/news/environment/2023/02/20/1983-downtown-salt-lake-turned/">several parts of the West</a> and extensive crop damage.</p>
<p><iframe id="V7dT9" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/V7dT9/8/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>This year, portions of the Southern Sierra Nevada have passed 1983’s levels, and <a href="https://www.latimes.com/california/story/2023-04-06/california-tulare-lake-storms-flooding-satellite-photos">Tulare Lake</a> is filling up again for the <a href="https://www.cnbc.com/2023/04/04/a-long-dormant-lake-has-reappeared-in-california-bringing-havoc-along-with-it.html">first time in decades</a>. Tulare Lake is an indication of just how extreme this year has been, and the risk is rising as the snow melts.</p>
<h2>The transition from extreme drought in 2022 to record snow was fast. Is that normal?</h2>
<p>California and some other parts of the West are known for weather whiplash. We frequently go from too dry to too wet. </p>
<p>2019 was another above-average year in terms of precipitation in California, but after that we saw <a href="https://droughtmonitor.unl.edu/DmData/TimeSeries.aspx">three straight years of drought</a>. We went from 13 strong or greater magnitude atmospheric rivers in 2017 to just three in 2020 and 2021, combined.</p>
<figure class="align-center ">
<img alt="Map showing well-above average precipitation across California, Nevada and Utah in particular." src="https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=724&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=724&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=724&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=910&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=910&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521088/original/file-20230414-28-qttrjl.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=910&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The onslaught of powerful atmospheric rivers pushed precipitation to well above average across large parts of the West in 2023, following three years of severe drought.</span>
<span class="attribution"><a class="source" href="https://cw3e.ucsd.edu/">Center for Western Weather and Water Extremes, Scripps Institution of Oceanography</a></span>
</figcaption>
</figure>
<p>California relies on these storms for <a href="https://water.ca.gov/News/Blog/2020/October/Atmospheric-Rivers-and-Their-Impact-on-California-Reservoirs">about half its water supply</a>, but if the West gets too many atmospheric rivers back to back, that starts to have harmful impacts, like the heavy snowpack that <a href="https://kslnewsradio.com/1994522/snow-causing-roofs-to-collapse-across-the-state-expert-offers-helpful-tips/">collapsed roofs</a> in the mountains this year, and <a href="https://youtu.be/sKx-wSICxQQ">flash flooding</a> and <a href="https://www.cbsnews.com/video/california-dangerous-mudslides-after-storms/#x">landslides</a>. These successive storms are typically referred to as <a href="https://cw3e.ucsd.edu/cw3e-publication-notice-atmospheric-river-families-definition-and-associated-synoptic-conditions/">atmospheric river families</a> and can result in exacerbated hydrologic impacts by quickly saturating soils and not allowing rivers and streams to recede back to base flow between storms.</p>
<h2>Are atmospheric rivers becoming more intense with a warming climate?</h2>
<p>There’s been <a href="https://theconversation.com/atmospheric-river-storms-can-drive-costly-flooding-and-climate-change-is-making-them-stronger-128902">a lot of research</a> on the impact of temperature because of how reliant California is on these storms for its water supply.</p>
<p>Atmospheric rivers are long, narrow corridors of water vapor in the sky that <a href="https://www.usgs.gov/news/featured-story/rivers-sky-6-facts-you-should-know-about-atmospheric-rivers">typically start in the tropics</a> as water evaporates and is pulled poleward by atmospheric circulations. They carry a lot of moisture – on average, their water vapor transport is more than <a href="https://doi.org/10.1175/JHM-D-17-0036.1">twice the flow of the Amazon River</a>. When they reach land, mountains <a href="https://www.noaa.gov/stories/what-are-atmospheric-rivers">force the air to rise</a>, which wrings out some of that moisture.</p>
<p>In a warming climate, the warmer air can hold more moisture. That can increase the capacity of atmospheric rivers, with more water vapor resulting in stronger storms.</p>
<figure class="align-center ">
<img alt="An animation shows two atmospheric rivers moving across the Pacific Ocean from the tropics." src="https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&rect=107%2C43%2C767%2C499&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=332&fit=crop&dpr=1 600w, https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=332&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=332&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=418&fit=crop&dpr=1 754w, https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=418&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/521070/original/file-20230414-18-eukcdy.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=418&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An example of an atmospheric river approaching the West Coast.</span>
<span class="attribution"><a class="source" href="http://tropic.ssec.wisc.edu/real-time/mtpw2/product.php?color_type=tpw_nrl_colors&prod=global2&timespan=24hrs&anim=anigf">Space Science and Engineering Center, University of Wisconsin-Madison</a></span>
</figcaption>
</figure>
<p>Research by some of my colleagues at Scripps Institution of Oceanography also suggests that California will <a href="https://doi.org/10.1038/s41598-022-15474-2">see fewer storms that aren’t atmospheric rivers</a>. But the state will likely see <a href="https://doi.org/10.1038/s41598-017-11285-y">more intense atmospheric rivers</a> as temperatures rise. California will be even more reliant on these atmospheric rivers for its snow, which will result in drier dries and wetter wets.</p>
<p>So, we’re likely to see this whiplash continue, but to a more extreme level, with longer periods of dry weather when we’re not getting these storms. But when we do get these storms, they have the potential to be more extreme and then result in more flooding.</p>
<p>In the more immediate future, we’re likely <a href="https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml">headed into an El Niño</a> this year, with warm tropical Pacific waters that shift weather patterns around the world. Typically, El Niño conditions are associated with more atmospheric river activity, especially in Central and Southern California.</p>
<p>So, we may see another wet year like this again in 2024.</p><img src="https://counter.theconversation.com/content/203874/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chad Hecht receives funding from California Department of Water Resources, U.S. Army Corps of Engineers, Sonoma Water, Yuba Water Agency, & Orange County Water District. </span></em></p>This year’s Sierra snowpack is looking a lot like 1983’s, and that was a year of flooding and mudslide disasters. A meteorologist explains what’s ahead.Chad Hecht, Research and Operations Meteorologist, Center for Western Weather and Water Extremes, University of California, San DiegoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/2017422023-03-14T12:24:57Z2023-03-14T12:24:57ZWhy rain on snow in the California mountains worries scientists<figure><img src="https://images.theconversation.com/files/515057/original/file-20230314-17-sv7ygq.jpg?ixlib=rb-1.1.0&rect=0%2C31%2C5200%2C3464&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A series of atmospheric rivers in early 2023 covered the Sierra Nevada in snow.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/in-an-aerial-view-a-person-shovels-on-a-snowy-roadway-lined-news-photo/1473159767">Mario Tama/Getty Images</a></span></figcaption></figure><p><em>Another round of powerful atmospheric rivers is hitting California, following storms in January and February 2023 that dumped record amounts of snow. This time, the storms are warmer, and they are <a href="https://twitter.com/NWSWPC/status/1635405410449358848/photo/1">triggering flood warnings</a> as they bring rain higher into the mountains – on top of the snowpack.</em></p>
<p><em>Professor <a href="https://www.colorado.edu/instaar/keith-musselman">Keith Musselman</a>, who studies water and climate change at the University of Colorado’s Institute of Arctic and Alpine Research, explained the complex risks rain on snow creates and how they might change in a warming climate.</em></p>
<h2>What happens when rain falls on snowpack?</h2>
<p>For much of the United States, storms with heavy rainfall can coincide with seasonal snow cover. When that happens, the resulting runoff of water can be much greater than what is produced from rain or snowmelt alone. The combination has resulted in <a href="https://data.sacriver.org/assets/5ffd2763a1b5d1a3078c4bd991651244/application/pdf/Flooding_from_rain-on-snow_events_in_the_Sierra_Nevada.pdf">some of the nation’s</a> most destructive and costly floods, including the <a href="https://www.weather.gov/media/publications/assessments/Flood_Northeast_1996.pdf">1996 Midwest floods</a> and the 2017 flood that <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2020GL088189">damaged California’s Oroville Dam</a>.</p>
<p>Contrary to common belief, rainfall itself has limited energy to melt snow. Rather, it is the warm temperatures, strong winds and high humidity, which can transport substantial energy in the form of <a href="https://www.britannica.com/science/latent-heat">latent</a> and <a href="https://energyeducation.ca/encyclopedia/Sensible_heat">sensible heat</a>, <a href="https://citeseerx.ist.psu.edu/document?repid=rep1&type=pdf&doi=1bbb9311d5932d6cdef0600ec16a4f124fde082d">that predominantly drive snowmelt</a> during rain-on-snow events.</p>
<p>Snowpack has air spaces that water can move through. As the rain falls, the water can travel relatively rapidly through the snowpack’s layers to reach the underlying soil. How streams respond to that runoff depends on how much water is already flowing and how saturated the soil is. </p>
<p>When the soil isn’t yet saturated, it can dampen or delay a flood response by soaking up rain and melting snow. But when the ground is saturated, snowmelt combined with rain can lead to fast and devastating flooding.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1635405410449358848"}"></div></p>
<p>One of the challenges for dealing with these rain-on-snow events is that the flood risk is hard to forecast.</p>
<p>To predict whether a flood will occur requires knowledge of weather and hydrological conditions. It requires knowing the soil moisture and snowpack conditions before the storm, the elevation at which rain transitions to snow, the rainfall rate, the wind speed, air temperature and humidity, and estimates of how those factors contribute to snowmelt. Additionally, each factor varies in time during a storm and varies in complex ways, especially across a mountainous landscape.</p>
<p>This is why rain-on-snow floods are characterized as <a href="https://journals.ametsoc.org/view/journals/bams/88/3/bams-88-3-319.xml">compound extreme events</a>. Despite the extensive damage they can cause, it may be surprising how little is known about how they vary in time, spatial extent and intensity.</p>
<h2>California is getting another atmospheric river, with more rain on snow expected. How does the rain-on-snow effect differ by elevation in the mountains there?</h2>
<p>In the California mountains right now, it’s the middle elevations that people need to pay attention to.</p>
<p>The lower elevations have primarily seen rainfall rather than snow, so there is less snowpack to melt. And in the highest elevations, colder temperatures promote the continued accumulation of deep snowpack and rainfall is less likely.</p>
<p>In <a href="https://doi.org/10.1175/JHM-D-20-0028.1">the middle transition zone</a> – where either substantial rainfall or snowfall can occur – rain-on-snow events are most common, causing both melting and risk of roof collapses.</p>
<p>If all storms were created equal, there would be well-defined rain zones and snow zones, and the rain-on-snow flood risk would be low. But that isn’t what happens. Instead, not only does the snow zone elevation vary during an event, but it also varies substantially from one storm to the next.</p>
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<p>The most destructive rain-on-snow events occur when rivers are already running high and soils are saturated, which can occur in response to a series of warm atmospheric rivers interacting with a deep snowpack – like California’s mountains have right now. The order in which these storms occur – or the storm sequencing – is especially important for assessing flood risk because these events are, in part, caused by rapid shifts between cold periods of snow accumulation followed by warm rainfall events.</p>
<h2>What does research show about the future risk of rain-on-snow events in a warming climate?</h2>
<p>Even less is known about how rain-on-snow flood risk may respond as the planet warms.</p>
<p>In a warmer climate, there will be less risk of rain falling on snow in the lower elevations <a href="https://doi.org/10.1038/s41612-018-0012-1">as the snowpack declines</a>, particularly in warmer regions such as the Pacific Northwest.</p>
<p>But at higher elevations, <a href="https://doi.org/10.1175/JCLI3850.1">more frequent rain-on-snow</a> events are expected. While <a href="https://doi.org/10.3354/cr00953">warmer temperatures</a> are expected to increase rainfall intensity, research shows that’s not the most important driver of this risk. Much of the expected increase in rain-on-snow flood risk is a result of the <a href="https://doi.org/10.1038/s41558-018-0236-4">rain-snow transition zone expanding higher</a> in elevation to include alpine areas that historically received predominantly snowfall.</p>
<p>Flood control and reservoir management systems in these mountainous regions will have to consider these future changes in rain-on-snow events – in addition to changes in rainfall intensity and storm sequencing – to <a href="https://doi.org/10.1038/s41558-018-0236-4">fully understand and prepare for</a> the local flood risk as the planet warms.</p>
<p>So, will projected increases in precipitation extremes and winter rainfall increase rain-on-snow occurrence and the associated flood risk? Or will less snow cover and larger soil moisture deficits reduce rain-on-snow flood risk in a warmer climate?</p>
<p>In a future climate, the response of rain-on-snow flood risk is expected to change in complex and often contradictory ways. The projected changes are <a href="https://doi.org/10.1038/s41558-018-0236-4">likely to vary</a> by region, season, climate model, emissions scenario and future time horizon. It’s a <a href="https://www.rms.com/newsroom/press-releases/press-detail/2023-01-25/moodys-rms-estimates-us5-7-billion-in-total-us-economic-losses-from-california-flooding">costly risk</a> that requires more research.</p><img src="https://counter.theconversation.com/content/201742/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Keith Musselman does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Rain falling on deep snow from a series of atmospheric rivers has heightened California’s flood risk. It’s a growing problem as the planet warms.Keith Musselman, Assistant Professor in Geography, Mountain Hydrology, and Climate Change, University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1983222023-01-24T12:48:28Z2023-01-24T12:48:28ZWhy forecasting snow is so difficult in the UK<figure><img src="https://images.theconversation.com/files/505873/original/file-20230123-7706-p65rcm.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5046%2C3366&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">It's hard to tell whether or not snow is on its way in the UK</span> <span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/traditional-red-english-public-phone-post-65450200">RTimages/Shutterstock</a></span></figcaption></figure><p>Cold winter weather in the UK almost always brings with it talk of snow.</p>
<p>British people tend to approach weather forecasts of snow with a combination of excitement and trepidation. Who doesn’t like the sight of unspoilt snow glittering over the rooftops like a Christmas card? But not many people enjoy the aftermath – an ice slush nightmare, soaking up the dirt from our streets and roads. </p>
<p>Forecasting snow is tricky in Britain though. And predictions tend to be uncertain. By the time British people reach adulthood, particularly those who live in southern England, a lot learn to treat forecasts of snow with cynicism. You might go to bed delighted by forecasts of snow only to wake the next day greeted by rain.</p>
<p>The UK’s erratic winter weather is caused by two things: its location and the fact that small differences in temperature can cause dramatic changes to the forecast. </p>
<p>The UK is located right where a <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/atmosphere/weather-fronts">number of different global weather systems converge</a>. Unlike many places in the world, freezing weather in Britain is generally accompanied by northerly or easterly winds. But heavy precipitation (liquid or frozen water) is usually from the west. Colder weather in the <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/seasons/winter/factors-that-influence-uk-winters">UK makes precipitation less likely</a>. Which is why if we see snow, it often arrives as a light shower or flurry. </p>
<p>Thick snow usually happens when precipitation from the west hits cold air from the east or north. </p>
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<h2>Don’t shoot the messenger</h2>
<p>Weather forecasting has come a long way over the last four decades. Improved computing, satellites, transformed communication and data science have made weather forecasting much more accurate. In 2022, <a href="https://theconversation.com/storm-eunice-how-forecasters-predicted-super-strong-winds-days-before-it-even-formed-177487">storm Eunice</a> and the <a href="https://theconversation.com/heatwave-why-extreme-weather-forecasts-have-improved-so-much-186261">summer 40°C heatwave</a> are both examples of how much forecasting has improved. It is not only able to accurately predict “normal” weather, but also when extreme weather will occur. </p>
<p>Forecasters today can predict widespread precipitation down to the hour. So mapping out wet weather is not the problem. The issue is that British winters make it a lot harder to tell what form precipitation will take when it reaches us. </p>
<p>This means predicting whether we will get sleet, <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/rain/freezing-rain">freezing rain</a>, snow or just rain. If you watch weather forecasts on a regular basis you will probably have heard the vague phrase “<a href="https://www.mirror.co.uk/news/uk-news/uk-weather-brits-braced-arctic-29018485#:%7E:text=wintry%20precipitation">wintry precipitation</a>”. This is the forecaster wrangling with an uncertain forecast as the term covers everything from rain to snow. </p>
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<p>A lot of the rain that we see in the UK, at all times of year, was snow when it started falling, but has fallen into air that is warmer than 0⁰C and melted. That means when forecasters predict rain, they are often predicting melted snow. If it’s 20⁰C in the summer, there is no doubt that by the time the snow reaches the ground it will have turned to rain. </p>
<p>For many places in the world the reverse is true. If the temperature is going to be -10⁰C, it <a href="https://weather.com/storms/winter/news/2022-12-%2023-winter-storm-elliott-bomb-cyclone-midwest-northeast-winds-snow">will settle on the ground as snow</a>. Back in 2018, in the UK the <a href="https://www.theguardian.com/uk-%20news/2018/mar/01/beast-from-east-storm-emma-uk-worst-weather-years">Beast from the East</a> brought with it temperatures so low the meteorologists could confidently predict snow. </p>
<h2>A headache for weather forecasters</h2>
<p>Most of the time, however, UK weather forecasters are working with expected temperatures close to 0°C. In this case a very small change to the temperature totally changes the weather. Weather forecasts tend to be accurate down to a couple of °C. But when your baseline is 0°C then a rise of 2⁰C will mean the snow melts and we get rain. But 2⁰C colder and it’s just snow. Somewhere in the middle creates sleet. </p>
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<p>And this is the other main reason why predicting snow is so hard in the UK. A small difference in temperature makes a really big difference to the outcome.</p>
<p>Precipitation lowers the air temperature. Heavier rain drops the temperature even more. Heavier sleet turns to snow. This means that even if the temperature of the system is predicted correctly, the fine details of the rate of precipitation will affect the form. It just so happens that much of the wintry weather in the UK falls at the temperature that makes the outcome sensitive to tiny changes. So, I’m afraid the phrase “wintery precipitation” is here to stay.</p><img src="https://counter.theconversation.com/content/198322/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Rob Thompson receives funding from ESA and previously NERC.</span></em></p>It’s important to be prepared for snow but UK winter weather forecasts can be unreliable. Here’s why.Rob Thompson, Postdoctoral Research Scientist in Meteorology, University of ReadingLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1962692023-01-12T18:29:43Z2023-01-12T18:29:43ZHow do snowflakes form? Is each snowflake really unique? Why is some snow light and fluffy or heavy? The amazing science of snow<figure><img src="https://images.theconversation.com/files/504098/original/file-20230111-46586-breuxu.jpg?ixlib=rb-1.1.0&rect=0%2C75%2C656%2C479&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">If you catch a snowflake, take a moment to look at it: It's a formation no one has ever seen before.</span> <span class="attribution"><span class="source">(Damian McCoig/Unsplash)</span></span></figcaption></figure><iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/how-do-snowflakes-form-is-each-snowflake-really-unique-why-is-some-snow-light-and-fluffy-or-heavy-the-amazing-science-of-snow" width="100%" height="400"></iframe>
<p>In northern communities, <a href="https://www.cbc.ca/news/canada/saskatchewan/year-weather-2022-1.6693807">seasonal snow plays a central role</a> in day-to-day activities. </p>
<p>For some, it means a day off from school. For others, it’s a signal that <a href="https://www.cbc.ca/sports/u-sports-notebook-jan-10-1.6708008">skiing season is starting</a>. Or maybe it’s a harbinger of an extra long <a href="https://barrie.ctvnews.ca/wicked-winter-system-creates-messy-driving-conditions-1.6193962">commute to work</a>. It’s remarkable how many memories and emotions can be evoked by a few billion tiny ice crystals.</p>
<p>We may see snow as a blanket or drifts across the landscape or our driveway. But when was the last time you took a closer look at snow, and I mean a really close look? </p>
<p>Many a writer has mused about snowflakes as a <a href="https://libquotes.com/henry-david-thoreau/quote/lbr3v4q">natural work</a> of art. Here’s a scientific look at the amazing nature of snowflakes and snow.</p>
<figure class="align-center ">
<img alt="A person catching snow in their mouth smiling." src="https://images.theconversation.com/files/504090/original/file-20230111-20-92bhy6.jpg?ixlib=rb-1.1.0&rect=0%2C498%2C2627%2C1410&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/504090/original/file-20230111-20-92bhy6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=394&fit=crop&dpr=1 600w, https://images.theconversation.com/files/504090/original/file-20230111-20-92bhy6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=394&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/504090/original/file-20230111-20-92bhy6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=394&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/504090/original/file-20230111-20-92bhy6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=495&fit=crop&dpr=1 754w, https://images.theconversation.com/files/504090/original/file-20230111-20-92bhy6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=495&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/504090/original/file-20230111-20-92bhy6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=495&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">When was the last time you caught a snowflake?</span>
<span class="attribution"><span class="source">THE CANADIAN PRESS/Darryl Dyck</span></span>
</figcaption>
</figure>
<h2>How do snowflakes form?</h2>
<p>While different catalogues will say that there are <a href="https://archive.las.iastate.edu/2014/01/17/how-snowflakes-get-their-shapes/">seven types of snowflakes</a>, <a href="https://www.compoundchem.com/2014/12/10/snowflakes/">or eight</a> <a href="https://www.smithsonianmag.com/smart-news/snowflakes-all-fall-one-35-different-shapes-180953760/">or 35</a>, we are probably most familiar with <a href="https://www.buffalo.edu/news/tipsheets/2018/001.html">the classic six-sided dendrite forms</a>, characterized by elaborate and nearly symmetrical branches. You know, the type that you would <a href="https://assets.marthastewart.com/d18/snowflake-template/snowflake-template.pdf">cut out of a piece of paper</a>. </p>
<p>The dendrite form is a study in water chemistry. When ice forms at the molecular level, the angle between the hydrogen and oxygen atoms will always <a href="http://www.ankn.uaf.edu/curriculum/athabascan/observingsnow/stuff.html#">be 120 degrees</a>;
put three of these together to get a full ring of molecules with a six-sided structure. In fact, every time a water molecule attaches itself to this ring, it will do so at the same angle. </p>
<p>As the snowflake grows, the attachment of water molecules is determined <a href="https://scied.ucar.edu/learning-zone/storms/snowflakes#">by the temperature</a> and humidity of the air. Since these characteristics don’t change too much at the size of a growing snowflake, those attachments tend to occur evenly across the six points of the hexagonal flake. </p>
<p>Molecule by molecule, the snowflake grows and eventually begins to fall. This takes the snowflake to a <a href="https://education.nationalgeographic.org/resource/atmosphere">new part of the atmosphere</a>, where temperature and humidity are different, resulting in new ice structures forming, but still with the same set of angles.</p>
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<figcaption><span class="caption">Video about ice and snow crystal growth with physics professor Ken Libbrecht.</span></figcaption>
</figure>
<h2>Is each snowflake really unique?</h2>
<p>A typical dendrite is made up of <a href="https://www.snexplores.org/article/how-snowflake-made">about a quintillion</a> (that’s a one with 18 zeroes after it) individual water molecules. Given slight changes in temperature and humidity and the huge number of molecules and bonding opportunities involved, the ice structures created can be incredibly diverse and complicated.</p>
<p>For this reason, it is entirely likely that no two snowflakes form in exactly the same way, and consequently no two snowflakes are alike. </p>
<p><a href="https://www.newscientist.com/article/mg25233653-800-kenneth-libbrecht-interview-a-grand-unified-theory-of-snowflakes/">Twin snowflakes have been grown in a lab</a>, where temperature and humidity are closely controlled, but that’s a bit of a cheat.</p>
<h2>Why is some snow light and fluffy and some is heavy?</h2>
<figure class="align-right ">
<img alt="A red cardinal sits in snowy branches as snow falls all around." src="https://images.theconversation.com/files/503870/original/file-20230110-4890-h790cv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/503870/original/file-20230110-4890-h790cv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=692&fit=crop&dpr=1 600w, https://images.theconversation.com/files/503870/original/file-20230110-4890-h790cv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=692&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/503870/original/file-20230110-4890-h790cv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=692&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/503870/original/file-20230110-4890-h790cv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=870&fit=crop&dpr=1 754w, https://images.theconversation.com/files/503870/original/file-20230110-4890-h790cv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=870&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/503870/original/file-20230110-4890-h790cv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=870&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Freshly fallen snow tends to be light and fluffy because the flakes take up a lot of space.</span>
<span class="attribution"><span class="source">THE CANADIAN PRESS/Justin Tang</span></span>
</figcaption>
</figure>
<p>The story of snow crystal growth doesn’t end high above in the clouds. Once the snowflakes reach the ground and accumulate as a blanket of snow, they begin to change. </p>
<p>Freshly fallen snow tends to be light and fluffy because the flakes take up a lot of space and there is a lot of air between and within them. But over time, they break apart, pack tighter together and the density increases. </p>
<p>This process <a href="https://doi.org/10.3189/S0022143000019535">is known as sintering</a> and is useful for building snow shelters like igloos and quinzees. But some of the most remarkable changes happen at the bottom of the snowpack, where warmth from the ground below and cold from the air above interact. </p>
<p>Through a process of sublimation — water molecules change from ice directly to vapour, skipping the liquid phase — and refreezing, cup-shaped crystals a few centimetres across <a href="https://utahavalanchecenter.org/blog/28021">known as depth hoar</a> can form. Though beautiful to look at, depth hoar has a low density and when it forms on a steep slope there is a chance for the snowpack to slide as an avalanche.</p>
<p>So next time you’re out in the snow, even if you’re grumbling about having to shovel the driveway for the umpteenth time this winter, take a moment to catch a snowflake on your mitten and have a look at it. You’re looking at a formation
no one has ever seen before.</p>
<p>Check out physics professor <a href="https://press.princeton.edu/books/hardcover/9780691200378/snow-crystals">Kenneth Libbrecht’s</a> website <a href="http://www.snowcrystals.com/">for a full description</a> of snowflake forms.</p><img src="https://counter.theconversation.com/content/196269/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Krystopher Chutko does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Molecule by molecule, a snowflake grows and eventually begins to fall. A scientific look at the amazing nature of snowflakes and snow.Krystopher Chutko, Assistant Professor, Department of Geography and Planning, University of SaskatchewanLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1971902023-01-10T22:02:33Z2023-01-10T22:02:33ZTaking fitness outside: 9 tips for becoming more active through the Canadian winter<figure><img src="https://images.theconversation.com/files/503753/original/file-20230110-14-gm9uml.JPG?ixlib=rb-1.1.0&rect=97%2C516%2C4461%2C2806&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Thick snow covers tree branches as people walk along a street in Ottawa after a snowstorm.</span> <span class="attribution"><span class="source">THE CANADIAN PRESS/Justin Tang</span></span></figcaption></figure><p>If you made a New Year’s resolution about physical activity, you are not alone. <a href="https://www.ipsos.com/en-ca/canadians-quick-make-new-years-resolutions-slow-see-them-through">Many Canadians make resolutions, and most focus on moving more</a>. Despite best intentions, it can be difficult for people to <a href="https://doi.org/10.1371%2Fjournal.pone.0234097">maintain New Year’s goals; in fact, nearly half fail to achieve their resolution</a>. There are many reasons for this, and one is that physical activity goals are hard to achieve, regardless of the time of year. </p>
<p>As researchers in the fields of behavioural medicine, physical activity and outdoor recreation, we have some ideas about how to make those resolutions stick.</p>
<p>Try to change up your physical activity and make it fun and enjoyable. Research shows that <a href="https://doi.org/10.3389/fpsyg.2020.577522">adherence to physical activity is improved when you mix things up and choose an activity that fills your cup</a>. </p>
<p>One way to increase variety and enjoyment might be choosing outdoor physical activities. And it seems Canadians (<a href="https://doi.org/10.1007/s00520-020-05938-4">with</a> and <a href="https://www.statista.com/statistics/1334779/share-canadians-engaging-outdoor-recreational-activities-by-frequency/">without</a> chronic conditions) desire outdoor activity, especially since the <a href="https://ccpr.parkpeople.ca/2021/overview/lessons">COVID-19 pandemic</a>. </p>
<h2>Outdoor benefits</h2>
<p>Taking your physical activity outside comes with some added benefits. We have found that a single trail walk can reduce participants’ reported levels of anxiety, and that after <a href="https://doi.org/10.1186/s41241-020-00094-x">eight weeks of trail walking two times per week, stress is decreased</a>. We also know that people who engage in physical activity <a href="https://doi.org/10.1016/j.healthplace.2009.03.002">outdoors stick to it better and longer</a>, and may <a href="https://doi.org/10.1016/j.ypmed.2016.06.016">work harder than when exercising indoors</a>. </p>
<figure class="align-center ">
<img alt="A woman in red snow-pants and a blue jacket holding a yellow snow shovel and tossing snow into the air while a dog leaps into the air" src="https://images.theconversation.com/files/503758/original/file-20230110-17-ar95nv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/503758/original/file-20230110-17-ar95nv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=472&fit=crop&dpr=1 600w, https://images.theconversation.com/files/503758/original/file-20230110-17-ar95nv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=472&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/503758/original/file-20230110-17-ar95nv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=472&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/503758/original/file-20230110-17-ar95nv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=593&fit=crop&dpr=1 754w, https://images.theconversation.com/files/503758/original/file-20230110-17-ar95nv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=593&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/503758/original/file-20230110-17-ar95nv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=593&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Shovelling snow counts as intense physical activity. Be the neighbourly snow shoveller, just ensure that you are warmed up and don’t go too hard.</span>
<span class="attribution"><span class="source">THE CANADIAN PRESS/Ryan Remiorz</span></span>
</figcaption>
</figure>
<p>This may be explained in part by the shift in focus outwards, to the environment, rather than on inner bodily sensations, making the exercise feel easier. </p>
<p>In a recent study currently under peer review, we (Thomson and Lesser) found that individuals with both low and high functional capacity (a measure of aerobic fitness) were able to complete hikes of varied difficulty. Those who were less fit simply slowed down to be able to complete the same hike at the same level of effort as their fit counterparts. </p>
<p>This suggests that outdoor physical activity, such as hiking, is feasible from a fitness perspective and is perceived as easier.</p>
<h2>The great outdoors in winter</h2>
<p>If you live in a four-season climate, you may be wondering how to take physical activity outside during a Canadian winter. </p>
<p>First and foremost, if you are just getting started, determine your readiness to move more. You can try an online assessment like the <a href="https://csep.ca/wp-content/uploads/2021/05/GETACTIVEQUESTIONNAIRE_ENG.pdf">Get Active Questionnaire</a> to see if you need to talk to your doctor first. </p>
<p>Next, try some of these tips and considerations:</p>
<h2>1. Find a support system</h2>
<p>Research has shown that <a href="https://doi.org/10.1080/1750984X.2016.1183222">social support can promote sustained physical activity behaviour</a>, and may take on even greater importance when activity moves outdoors.</p>
<h2>2. Dress in layers</h2>
<p>Overdressing is always better than underdressing, and <a href="https://adventure.howstuffworks.com/outdoor-activities/hiking/wool-when-wet.htm">wool is your best bet</a> to reduce moisture and keep in heat. Make sure you are covered from head to toe — that means wearing a scarf to help warm the incoming air when the temperatures plummet.</p>
<h2>3. Have a plan B</h2>
<p>Unfortunately, depending on where you live, it might be too cold or icy to be outdoors. In this case, take a break and move it inside for a bit. That way, you can continue your active lifestyle and build up some excitement about getting back outside when the weather improves.</p>
<h2>4. Safety First</h2>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/503767/original/file-20230110-14-99arna.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Image of the bottoms of a pair of shoes with orange soles, displaying two types of external ice cleats" src="https://images.theconversation.com/files/503767/original/file-20230110-14-99arna.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/503767/original/file-20230110-14-99arna.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/503767/original/file-20230110-14-99arna.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/503767/original/file-20230110-14-99arna.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/503767/original/file-20230110-14-99arna.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/503767/original/file-20230110-14-99arna.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/503767/original/file-20230110-14-99arna.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Two kinds of exterior cleats attached to running shoes.</span>
<span class="attribution"><span class="source">(AP Photo/Dan Joling)</span></span>
</figcaption>
</figure>
<p>When it gets slippery outside, ensure that you have proper footwear. We love snow cleats that can be put over your shoes to enhance your grip. You can also consider using walking poles to improve your balance and reduce the risk of falls.</p>
<h2>5. Hydrate</h2>
<p>Even though you might not feel as warm and sweaty as you would in warmer months, you are still losing water and you need to stay hydrated.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/cover-your-face-wear-a-hat-and-stay-hydrated-to-exercise-safely-through-the-winter-173807">Cover your face, wear a hat and stay hydrated to exercise safely through the winter</a>
</strong>
</em>
</p>
<hr>
<h2>6. Make it part of your day</h2>
<p>Find different ways to incorporate the outdoors into your daily activities! Did you know that <a href="https://theconversation.com/snow-shovelling-healthy-exercise-or-deadly-activity-129183">shovelling snow</a> counts as intense physical activity? Be the neighbourly snow shoveller — just ensure that you are warmed up and don’t go too hard. If you love biking to work, try fat tires on your bike. They increase your traction on snow and ice. </p>
<p>If these sound a bit too strenuous, you can always park farther away at work, school or the grocery store to add some steps to your day, or consider taking a brief walk outside on your lunch break.</p>
<h2>7. Light it up</h2>
<p>With the days ending so early, it can be a challenge to fit in physical activity before the sun sets. A head lamp will allow you to be out early or past dark. Just ensure that you are in a safe location (and maybe bring someone from your support system along).</p>
<h2>8. Try something new</h2>
<figure class="align-center ">
<img alt="A blue sign picturing a snowshoer on a tree trunk with snow in the background" src="https://images.theconversation.com/files/503762/original/file-20230110-12-k3nhwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/503762/original/file-20230110-12-k3nhwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=416&fit=crop&dpr=1 600w, https://images.theconversation.com/files/503762/original/file-20230110-12-k3nhwk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=416&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/503762/original/file-20230110-12-k3nhwk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=416&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/503762/original/file-20230110-12-k3nhwk.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=523&fit=crop&dpr=1 754w, https://images.theconversation.com/files/503762/original/file-20230110-12-k3nhwk.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=523&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/503762/original/file-20230110-12-k3nhwk.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=523&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">If you’re interested in trying snowshoeing, winter hiking or cross-country skiing, consider borrowing equipment from a friend, renting from your local recreation facility or purchasing used equipment from a sports trader.</span>
<span class="attribution"><span class="source">THE CANADIAN PRESS/Graham Hughes</span></span>
</figcaption>
</figure>
<p>This is a perfect time to break out of your routine. Ever tried snowshoeing, winter hiking or cross-country skiing? Now could be the time. Don’t have equipment? Consider borrowing from a friend, renting from your local recreation facility or purchasing used equipment from a sports trader.</p>
<h2>9. Enjoy the tranquillity</h2>
<p>Outdoor experiences in winter tend to be quieter and include more expansive terrain with different sounds, wildlife and colour experiences. Try taking advantage of it and notice how you feel.</p>
<p>We hope you will try taking it outside to reap the benefits of our beautiful Canadian winters. Who knows, maybe you will even increase the likelihood of sticking to those hard-to-meet New Year’s resolutions in the process!</p><img src="https://counter.theconversation.com/content/197190/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>The authors do not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Taking your physical activity outside comes with added benefits. Here are ways to pursue your fitness goals outdoors, even in the middle of a Canadian winter.Iris Lesser, Assistant professor in kinesiology, University of The Fraser ValleyAmanda Wurz, Assistant Professor, School of Kinesiology, University of The Fraser ValleyCynthia Thomson, Assistant Professor in Kinesiology, University of The Fraser ValleyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1951722023-01-02T12:40:42Z2023-01-02T12:40:42ZScientists dig deep and find a way to accurately predict snowmelt after droughts<figure><img src="https://images.theconversation.com/files/497775/original/file-20221128-25-6d5d8u.jpg?ixlib=rb-1.1.0&rect=6%2C324%2C2293%2C1207&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Following historic drought in 2021, reservoir levels dropped down in the Hoover Dam on the Colorado River, which gets its waters from the melting snowpack from the Rocky Mountains of Colorado and Wyoming.</span> <span class="attribution"><a class="source" href="https://pxhere.com/en/photo/623841">(pxhere.com)</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/scientists-dig-deep-and-find-a-way-to-accurately-predict-snowmelt-after-droughts" width="100%" height="400"></iframe>
<p>Where does your water supply come from? </p>
<p>If you live near mountains, for instance in British Columbia, a lot of your water probably comes from mountain snowpack. Over <a href="https://doi.org/10.1038/s41586-019-1822-y">1.9 billion people</a> globally rely on the snow melting and running off from these mountain snowpacks for their water supply.</p>
<p>Accurate predictions of this annual trend is critical for water supply planning. And forecasting models often rely on the <a href="https://www.academia.edu/47863505/Principles_of_snow_hydrology">historical relationship between mountain snowpack and the subsequent water supply</a>. </p>
<p>However, in times of unprecedented drought and a changing climate, these forecasting models seem to no longer be reliable. Following an intense drought in California in 2021, <a href="https://www.theguardian.com/us-news/2021/jun/07/california-drought-oregon-west-climate-change">snowmelt from mountain snowpack delivered significantly less water than historical models predicted</a>, meaning that reservoirs remained drier than anticipated. For the first time in 100 years, water supply models were wrong. </p>
<p>In an attempt to address the gaps in the traditional model, we recently <a href="https://doi.org/10.1029/2022GL100505">developed an updated water supply forecasting model</a> that considers additional factors, like water storage deficits in the soil and bedrock. This new model significantly improves the accuracy of water supply forecasts following drought.</p>
<h2>What are existing water supply models missing?</h2>
<p><a href="https://doi.org/10.1017/CBO9780511535673">Models used for forecasting snowmelt </a>typically consider winter rain and snowpack. But it turns out that water absorbed by the ground matters too. The amount of water absorbed into the soil and bedrock varies from year to year and is especially impacted by drought.</p>
<p>When snow melts or rain falls, almost all of it goes underground first before <a href="https://www.usgs.gov/special-topics/water-science-school/science/runoff-surface-and-overland-water-runoff">heading downstream to water supply systems </a>. The water storage processes below the surface of the ground are key to understanding the ultimate fate of rain and snow in the mountains.</p>
<figure class="align-center ">
<img alt="Schematic diagram of runoff generation in the mountains." src="https://images.theconversation.com/files/497773/original/file-20221128-12-3ska04.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/497773/original/file-20221128-12-3ska04.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=460&fit=crop&dpr=1 600w, https://images.theconversation.com/files/497773/original/file-20221128-12-3ska04.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=460&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/497773/original/file-20221128-12-3ska04.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=460&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/497773/original/file-20221128-12-3ska04.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=578&fit=crop&dpr=1 754w, https://images.theconversation.com/files/497773/original/file-20221128-12-3ska04.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=578&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/497773/original/file-20221128-12-3ska04.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=578&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A diagram showing how water gets from snowpack or rain to water supply systems. Rain and snowmelt seep into the ground. Plants draw water from this region. Once the subsurface is wet, the water flows downstream to water supply systems.</span>
<span class="attribution"><a class="source" href="https://agupubs.onlinelibrary.wiley.com/doi/10.1029/2022GL100505">(Dana Lapides)</a>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>The below ground environment is made up of complex layers of soil, fractures and weathered bedrock that can <a href="https://hydrology.usu.edu/rrp/pdfs/ch2.pdf">store, detain and transport water</a>. The details of these processes are complicated, but the overall effect can be likened to a giant sponge. </p>
<p>Over the summer, the ground dries out and it gets wet again with the arrival of rain and snowmelt in winter and spring. Once the ground is wet enough, it starts to drip. This dripping water enters the groundwater and streams and eventually goes into the water supply systems.</p>
<p>How much water drips depends on how much snowmelt and rain is received, which is included in forecasting models. It also depends on how dry the subsurface was to begin with, which is not traditionally included in forecasting models.</p>
<h2>Plants use a lot of water</h2>
<p>How dry the subsurface is this year can depend on how much water the plants used last year (or even over the last few years). In hotter, drier years, plants can use more water from underground, causing the subsurface to dry out more.</p>
<p>Recent studies show us that <a href="https://doi.org/10.1038/s41586-021-03761-3">trees routinely dry up not just soils but also weathered bedrock metres below the surface</a>.</p>
<p>Scientists are still struggling to identify how dry these mountain environments can get and how far below the surface they dry. With a drier subsurface at the start of the year, more snowmelt is needed before water starts to flow downstream to water supply systems. </p>
<p>As droughts become more frequent and intense with climate change, this process could become more important even in regions that historically haven’t faced much drought.</p>
<h2>Measuring the moisture underground</h2>
<p>Directly observing the moisture levels of the ground’s subsurface is difficult, especially when it’s stored in weathered bedrock, which can extend many metres below the ground surface and be challenging to observe. </p>
<p>In our research, we found the most accurate measurements by lowering geophysical instruments down boreholes and taking water content readings at different depths. By comparing these readings over time, we observe how <a href="https://doi.org/10.1073/pnas.1800141115">the subsurface dries out and gets wet again</a>.</p>
<figure class="align-center ">
<img alt="Researcher measures subsurface wetness conditions" src="https://images.theconversation.com/files/497767/original/file-20221128-20492-5u0m49.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/497767/original/file-20221128-20492-5u0m49.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=429&fit=crop&dpr=1 600w, https://images.theconversation.com/files/497767/original/file-20221128-20492-5u0m49.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=429&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/497767/original/file-20221128-20492-5u0m49.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=429&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/497767/original/file-20221128-20492-5u0m49.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=539&fit=crop&dpr=1 754w, https://images.theconversation.com/files/497767/original/file-20221128-20492-5u0m49.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=539&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/497767/original/file-20221128-20492-5u0m49.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=539&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A USDA Forest Service employee uses an instrument to measure the moisture conditions deep underground.</span>
<span class="attribution"><span class="source">(Jamie Hinrichs/USDA Forest Service)</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>However, this intensive monitoring is nearly impossible to do over large areas.</p>
<p>While we can’t look directly underground everywhere, <a href="https://hess.copernicus.org/articles/20/1459/2016/">we can track how much water enters (rain and snowmelt) and leaves (plant water use) the ground using satellite-derived data</a>.</p>
<p>By taking a running account of water going in and out of the ground, we can estimate how dry the subsurface is — a metric we call the water storage deficit. </p>
<h2>Water supply models must dig deeper</h2>
<p>Our <a href="https://doi.org/10.1038/s41586-021-03761-3">newly-developed water supply forecasting model</a> accounts for water storage deficits in both soil and bedrock. This has improved post-drought forecast accuracy substantially, taking the probability of error in the calculation of predictions from 60 per cent to about 20 per cent.</p>
<p>Since we can calculate deficits before spring snowmelts, they serve as an early warning sign and can aid water management strategies.</p>
<p>As the climate changes, the water supply challenges in California foreshadow issues that will become increasingly prevalent in British Columbia and other regions reliant on mountain snowpack. Using updated forecasting models in the future can help these regions better prepare for <a href="https://drought.ca.gov/current-drought-conditions/#overview-of-2021">continued water shortages even when snowpack seems normal</a>.</p><img src="https://counter.theconversation.com/content/195172/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dana Ariel Lapides receives funding from Simon Fraser University and the US Forest Service Southwest Pacific Research Station with funds administered through Oak Ridge Institute for Science and Engineering (ORISE). </span></em></p><p class="fine-print"><em><span>David Dralle receives funding from the US Forest Service Pacific Southwest Research Station. </span></em></p><p class="fine-print"><em><span>Jesse Hahm receives funding from Simon Fraser University, the Natural Sciences and Engineering Research Council of Canada, the Canada Foundation for Innovation, and the Pacific Institute for Climate Solutions.</span></em></p><p class="fine-print"><em><span>Daniella Rempe does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Unprecedented droughts leave the subsurface drier than usual, affecting water supply in subsequent years.Dana Ariel Lapides, Postdoctoral Research Fellow, Geography, Simon Fraser UniversityDaniella Rempe, Assistant professor, Jackson School of Geosciences, The University of Texas at AustinDavid Dralle, Research officer, Hydrology, University of California, BerkeleyJesse Hahm, Department of Geography, Assistant Professor, Simon Fraser UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1962542022-12-13T16:01:45Z2022-12-13T16:01:45ZArctic Report Card 2022: The Arctic is getting rainier and seasons are shifting, with broad disturbances for people, ecosystems and wildlife<figure><img src="https://images.theconversation.com/files/500768/original/file-20221213-10619-mim3qd.jpg?ixlib=rb-1.1.0&rect=24%2C8%2C5439%2C3628&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Rainier winters make life more difficult for Arctic wildlife and the humans who rely on them.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/reindeer-herd-in-mid-winter-norwegian-arctic-january-27th-news-photo/608180463">Scott Wallace/Getty Image</a></span></figcaption></figure><p>In the Arctic, the freedom to travel, hunt and make day-to-day decisions is profoundly tied to cold and frozen conditions for much of the year. These conditions are rapidly changing as the Arctic warms.</p>
<p>The Arctic is now seeing more rainfall when historically it would be snowing. Sea ice that once protected coastlines from erosion during fall storms is forming later. And thinner river and lake ice is making travel by snowmobile increasingly life-threatening. </p>
<p>Ship traffic in the Arctic is also increasing, bringing new risks to fragile ecosystems, and the Greenland ice sheet is continuing to send freshwater and ice into the ocean, raising global sea level</p>
<p>In the annual <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022">Arctic Report Card</a>, released Dec. 13, 2022, we brought together 144 other Arctic scientists from 11 countries to examine the current state of the Arctic system.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500559/original/file-20221212-1585-avllq2.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Some of the Arctic headlines of 2022 discussed in the Arctic Report Card.</span>
<span class="attribution"><span class="source">NOAA Climate.gov</span></span>
</figcaption>
</figure>
<h2>The Arctic is getting wetter and rainier</h2>
<p>We found that <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/993/Precipitation">Arctic precipitation is on the rise across all seasons</a>, and these seasons are shifting. </p>
<p>Much of this new precipitation is now falling as rain, sometimes during winter and traditionally frozen times of the year. This disrupts daily life for humans, wildlife and plants. </p>
<p>Roads become dangerously icy more often, and communities face greater risk of river flooding events. For Indigenous reindeer herding communities, winter rain can create an impenetrable ice layer that prevents their reindeer from accessing vegetation beneath the snow. </p>
<figure class="align-center ">
<img alt="Map shows significant increases in precipitation across the Arctic in both winter and fall." src="https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=830&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=830&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=830&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1043&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1043&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500588/original/file-20221213-3149-u7oobq.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1043&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.arctic.noaa.gov/Report-Card">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>Arctic-wide, this shift toward wetter conditions can disrupt the lives of animals and plants that have evolved for dry and cold conditions, potentially altering Arctic peoples’ local foods.</p>
<p>When Fairbanks, Alaska, got 1.4 inches of freezing rain in December 2021, the moisture created an ice layer that persisted for months, bringing down trees and disrupting travel, infrastructure and the ability of some Arctic animals to forage for food. The resulting ice layer was largely <a href="https://www.ktoo.org/2022/12/06/one-third-delta-junction-bison-starve/">responsible for the deaths of a third of a bison herd</a> in interior Alaska.</p>
<p>There are multiple reasons for this increase in Arctic precipitation.</p>
<p>As sea ice rapidly declines, more open water is exposed, which feeds increased moisture into the atmosphere. The entire Arctic region has seen a more than <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/989/Sea-Ice">40% loss in summer sea ice extent</a> over the 44-year satellite record.</p>
<p>The Arctic atmosphere is also warming <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/992/Surface-Air-Temperature">more than twice as fast as the rest of the globe</a>, and this warmer air can hold more moisture. </p>
<figure class="align-center ">
<img alt="Map and time series chart show the continuing decline of the maximum extent of Arctic sea ice." src="https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=983&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=983&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=983&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1235&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1235&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500769/original/file-20221213-15012-yusnzh.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1235&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.arctic.noaa.gov/Report-Card">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>Under the ground, the wetter, rainier Arctic is accelerating the <a href="https://theconversation.com/thawing-permafrost-is-roiling-the-arctic-landscape-driven-by-a-hidden-world-of-changes-beneath-the-surface-as-the-climate-warms-174157">thaw of permafrost</a>, upon which most Arctic communities and infrastructure are built. The result is crumbling buildings, sagging and cracked roads, the emergence of sinkholes and the collapse of community coastlines along rivers and ocean. </p>
<p>Wetter weather also disrupts the building of a reliable winter snowpack and safe, reliable river ice, and often challenges Indigenous communities’ efforts to <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2019/ArtMID/7916/ArticleID/850/Voices-from-the-Front-Lines-of-a-Changing-Bering-Sea">harvest and secure their food</a>.</p>
<p>When <a href="https://theconversation.com/typhoon-merbok-fueled-by-unusually-warm-pacific-ocean-pounded-alaskas-vulnerable-coastal-communities-at-a-critical-time-190898">Typhoon Merbok</a> hit in September 2022, fueled by unusually warm Pacific water, its hurricane-force winds, 50-foot waves and far-reaching storm surge damaged homes and infrastructure over 1,000 miles of Bering Sea coastline, and disrupted hunting and harvesting at a crucial time.</p>
<figure class="align-center ">
<img alt="Globe and time series chart show temperatures rising faster across the Arctic than in the rest of the world." src="https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=774&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=774&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=774&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=972&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=972&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500589/original/file-20221213-900-rbisur.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=972&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.arctic.noaa.gov/Report-Card">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<h2>Arctic snow season is shrinking</h2>
<p>Snow plays critical roles in the Arctic, and the snow season is shrinking.</p>
<p>Snow helps to keep the Arctic cool by reflecting incoming solar radiation back to space, rather than allowing it to be absorbed by the darker snow-free ground. Its presence helps <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/1002/Lake-Ice">lake ice last longer into spring</a> and helps the land to retain moisture longer into summer, preventing overly dry conditions that are ripe for <a href="https://uaf-iarc.org/2022/12/a-future-of-more-wildfires-in-alaska/">devastating wildfires</a>.</p>
<p>Snow is also a travel platform for hunters and a habitat for many animals that rely on it for nesting and protection from predators.</p>
<p>A <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/991/Terrestrial-Snow-Cover">shrinking snow season</a> is disrupting these critical functions. For example, the June snow cover extent across the Arctic is declining at a rate of nearly 20% per decade, marking a dramatic shift in how the snow season is defined and experienced across the North. </p>
<p>Even in the depth of winter, warmer temperatures are breaking through. The far northern Alaska town of Utqiaġvik hit 40 degrees Fahrenheit (4.4 C) – <a href="https://www.washingtonpost.com/weather/2022/12/06/alaska-winter-temperature-record-utqiagvik/">8 F above freezing</a> – on Dec. 5, 2022, even though the sun does not breach the horizon from mid-November through mid-January.</p>
<figure class="align-center ">
<img alt="Map and time series chart show how June snowfall has decreased since the late 1970s." src="https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=863&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=863&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=863&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1085&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1085&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500590/original/file-20221213-22-drdove.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1085&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.arctic.noaa.gov/Report-Card">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>Fatal falls through thin sea, lake and river ice are <a href="https://doi.org/10.1093/pubmed/fdt081">on the rise</a> across Alaska, resulting in immediate tragedies as well as adding to the <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/1001/Consequences-of-Rapid-Environmental-Arctic-Change-for-People">cumulative human cost of climate change</a> that Arctic Indigenous peoples are now experiencing on a generational scale.</p>
<h2>Greenland ice melt means global problems</h2>
<p>The impacts of Arctic warming are not limited to the Arctic. In 2022, the <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/990/Greenland-Ice-Sheet">Greenland ice sheet lost ice for the 25th consecutive year</a>. This adds to rising seas, which escalates the danger coastal communities around the world must plan for to mitigate flooding and storm surge.</p>
<p>In early September 2022, the Greenland ice sheet experienced an <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/990/Greenland-Ice-Sheet">unprecedented late-season melt event across 36% of the ice sheet surface</a>. This was followed by another, even later melt event that same month, caused by the remnants of Hurricane Fiona moving up along eastern North America.</p>
<p>International <a href="https://omg.jpl.nasa.gov/portal/">teams of scientists</a> are dedicated to assessing the scale to which the Greenland ice sheet’s ice formation and ice loss are out of balance. They are also increasingly learning about the transformative role that warming ocean waters play.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=338&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=338&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=338&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=425&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=425&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500374/original/file-20221212-105279-65pkn0.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=425&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption"></span>
<span class="attribution"><span class="source">NOAA Climate.gov</span></span>
</figcaption>
</figure>
<p>This year’s Arctic Report Card includes <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/1007/Lessons-From-Oceans-Melting-Greenland-a-NASA-Airborne-Mission">findings from the NASA Oceans Melting Greenland (OMG) mission</a> that has confirmed that warming ocean temperatures are increasing ice loss at the edges of the ice sheet.</p>
<h2>Human-caused change is reshaping the Arctic</h2>
<p>We are living in a new geological age — <a href="https://nap.nationalacademies.org/catalog/18726/the-arctic-in-the-anthropocene-emerging-research-questions">the Anthropocene</a> — in which human activity is the dominant influence on our climate and environments.</p>
<p>In the warming Arctic, this requires decision-makers to better anticipate the interplay between a changing climate and human activity. For example, satellite-based ship data since 2009 clearly show that <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/1004/Satellite-Record-of-Pan-Arctic-Maritime-Ship-Traffic">maritime ship traffic</a> has increased within all Arctic high seas and national exclusive economic zones as the region has warmed.</p>
<figure class="align-center ">
<img alt="Map shows increase in ship traffic in Arctic regions since 2009, with a nearly 50% increase in shipping around Norway and over 12% increase near Russia. Paired with a photo of a ship in sea ice." src="https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=805&fit=crop&dpr=1 600w, https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=805&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=805&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1012&fit=crop&dpr=1 754w, https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1012&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/500591/original/file-20221213-23-cximvx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1012&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption"></span>
<span class="attribution"><a class="source" href="https://www.arctic.noaa.gov/Report-Card">NOAA Climate.gov</a></span>
</figcaption>
</figure>
<p>For these ecologically sensitive waters, this added ship traffic raises urgent concerns ranging from the future of Arctic trade routes to the introduction of even more human-caused stresses on Arctic peoples, ecosystems and the climate. These concerns are especially pronounced given uncertainties regarding the current geopolitical tensions between Russia and the other Arctic states over its war in Ukraine.</p>
<p>Rapid Arctic warming requires new forms of partnership and information sharing, including <a href="https://arctic.noaa.gov/Report-Card/Report-Card-2022/ArtMID/8054/ArticleID/1001/Consequences-of-Rapid-Environmental-Arctic-Change-for-People">between scientists and Indigenous knowledge-holders</a>. Cooperation and building resilience can help to reduce some risks, but global action to rein in greenhouse gas pollution is essential for the entire planet.</p><img src="https://counter.theconversation.com/content/196254/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Matthew Druckenmiller receives research funding from the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA). </span></em></p><p class="fine-print"><em><span>Rick Thoman receives funding from NOAA/Arctic Program</span></em></p><p class="fine-print"><em><span>Twila Moon receives research funding from the National Science Foundation (NSF) and the National Oceanic and Atmospheric Administration (NOAA).</span></em></p>The annual report is also a reminder that what happens in the Arctic affects the rest of the world.Matthew L. Druckenmiller, Research Scientist, National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado BoulderRick Thoman, Alaska Climate Specialist, University of Alaska FairbanksTwila A. Moon, Deputy Lead Scientist, National Snow and Ice Data Center (NSIDC), Cooperative Institute for Research in Environmental Sciences (CIRES), University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1949532022-11-18T20:03:54Z2022-11-18T20:03:54ZWhat causes lake-effect snow like Buffalo’s extreme storms?<figure><img src="https://images.theconversation.com/files/496302/original/file-20221120-6248-3fwep2.jpg?ixlib=rb-1.1.0&rect=0%2C13%2C2995%2C1976&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Parts of the Buffalo area saw more than 6 feet of snow over three days in November 2022.</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/APTOPIXWintryWeather/aeeb2499dca64e22ab85c9da7ae267ad/photo">AP Photo/Joshua Bessex</a></span></figcaption></figure><p>It’s hard for most people to imagine more than 4 feet of snow in one storm, but such extreme snowfall events happen along the eastern edges of the Great Lakes.</p>
<p>The phenomenon is called “lake-effect snow.”</p>
<p>It starts with cold, dry air from Canada. As the bitter cold air sweeps across the relatively warmer Great Lakes, it sucks up more and more moisture that falls as snow.</p>
<figure class="align-center ">
<img alt="A satellite image shows wind blowing snow across Lakes Superior, Michigan, Huron, Erie and Ontario on Nov. 20, 2014" src="https://images.theconversation.com/files/496201/original/file-20221118-12-5hv833.jpg?ixlib=rb-1.1.0&rect=18%2C18%2C6032%2C4027&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/496201/original/file-20221118-12-5hv833.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=401&fit=crop&dpr=1 600w, https://images.theconversation.com/files/496201/original/file-20221118-12-5hv833.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=401&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/496201/original/file-20221118-12-5hv833.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=401&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/496201/original/file-20221118-12-5hv833.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=504&fit=crop&dpr=1 754w, https://images.theconversation.com/files/496201/original/file-20221118-12-5hv833.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=504&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/496201/original/file-20221118-12-5hv833.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=504&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Canadian winds pick up moisture over the Great Lakes, turning it into heavy snowfall on the far shore.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/noaa_glerl/16056567472/">NOAA</a></span>
</figcaption>
</figure>
<p>I’m a <a href="https://scholar.google.com/citations?user=h3tGrwsAAAAJ&hl=en">climate scientist</a> at UMass Amherst. In the Climate Dynamics course I teach, students often ask how cold, dry air can lead to heavy snowfall. Here’s how that happens.</p>
<h2>How dry air turns into snowstorms</h2>
<p><a href="http://www.theweatherprediction.com/winterwx/lesnow/">Lake-effect snow</a> is strongly influenced by the differences between the amount of heat and moisture at the lake surface and in the air a few thousand feet above it. </p>
<p>A big contrast creates conditions that help to suck water up from the lake, and thus more snowfall. A difference of 25 degrees Fahrenheit (14 Celsius) or more creates an environment that can fuel heavy snows. This often happens in late fall, when lake water is still warm from summer and cold air starts sweeping down from Canada. More moderate lake-effect snows occur every fall under less extreme thermal contrasts.</p>
<p>The wind’s path over the lakes is important. The farther cold air travels over the lake surface, the more moisture is evaporated from the lake. A long “fetch” – the distance over water – often results in more lake-effect snow than a shorter one.</p>
<p>Imagine a wind out of the west that is perfectly aligned so it blows over the entire 241-mile length of Lake Erie. That’s close to what Buffalo experienced during a storm that brought 6 feet of snow to the region in November 2022.</p>
<figure class="align-center ">
<img alt="An animation overlays wind direction on satellite imagery of snow accumulation during a lake-effect event." src="https://images.theconversation.com/files/496208/original/file-20221118-11-imi2ax.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/496208/original/file-20221118-11-imi2ax.gif?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/496208/original/file-20221118-11-imi2ax.gif?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/496208/original/file-20221118-11-imi2ax.gif?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/496208/original/file-20221118-11-imi2ax.gif?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/496208/original/file-20221118-11-imi2ax.gif?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/496208/original/file-20221118-11-imi2ax.gif?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Wind directions from a storm in 2016 show how lake-effect snow piles up.</span>
<span class="attribution"><a class="source" href="https://noaaglerl.files.wordpress.com/2020/11/lakeeffectsnow_dec2016.gif">NOAA</a></span>
</figcaption>
</figure>
<p>Once the snow reaches land, elevation contributes an additional effect. Land that slopes up from the lake increases lift in the atmosphere, enhancing snowfall rates. This mechanism is termed “<a href="https://www.worldatlas.com/articles/what-is-orographic-precipitation.html">orographic effect</a>.” The <a href="https://tughill.org/tug-hill-region/">Tug Hill plateau</a>, located between Lake Ontario and the Adirondacks in western New York, is well known for its impressive snowfall totals.</p>
<p>In a typical year, annual snowfall in the “lee,” or downwind, of the Great Lakes approaches 200 inches in some places.</p>
<p>Residents in places like Buffalo, New York, are keenly aware of the phenomenon. In 2014, some parts of the region received upwards of 6 feet of snowfall during an <a href="https://www.weather.gov/buf/lake1415_stormb.html">epic lake-effect event</a>. The weight of the <a href="https://www.weather.gov/buf/lake1415_stormb.html">snow collapsed hundreds of roofs</a> and led to over a dozen deaths. </p>
<figure class="align-center ">
<img alt="Two people shovel knee-deep snow off a roof." src="https://images.theconversation.com/files/496230/original/file-20221118-24-nv4slv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/496230/original/file-20221118-24-nv4slv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=383&fit=crop&dpr=1 600w, https://images.theconversation.com/files/496230/original/file-20221118-24-nv4slv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=383&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/496230/original/file-20221118-24-nv4slv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=383&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/496230/original/file-20221118-24-nv4slv.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=481&fit=crop&dpr=1 754w, https://images.theconversation.com/files/496230/original/file-20221118-24-nv4slv.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=481&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/496230/original/file-20221118-24-nv4slv.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=481&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A lake-effect snowstorm in November 2014 buried Buffalo, N.Y., under more than 5 feet of snow and caused hundreds of roofs to collapse.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/residents-work-to-remove-snow-from-the-roof-on-november-21-news-photo/459384792">Patrick McPartland/Anadolu Agency/Getty Images</a></span>
</figcaption>
</figure>
<p>Lake-effect snowfall in the Buffalo area is typically confined to a narrow region where the wind is coming straight off the lake. Drivers on Interstate 90 often go from sunny skies to a blizzard and back to sunny skies over a distance of 30 to 40 miles.</p>
<h2>The role of climate change</h2>
<p>Is climate change playing a role in the lake-effect snow machine? To an extent. </p>
<p><a href="https://climatechange.chicago.gov/climate-impacts/climate-impacts-midwest">Fall has warmed across the upper Midwest</a>. Ice prevents lake water from evaporating into the air, and it is forming later than in the past. Warmer summer air has led to warmer lake temperature into fall.</p>
<p>Models predict that with additional warming, more lake-effect snow will occur. But over time, the warming will lead to more of the precipitation falling as lake-effect rain, which already occurs in early fall, rather than snow.</p><img src="https://counter.theconversation.com/content/194953/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Michael A. Rawlins receives funding from the Department of Energy, the National Aeronautics and Space Administration, and the National Science Foundation. </span></em></p>Snowstorms that sweep across the Great Lakes can dump several feet of snow on the other side. A climate scientists explains why.Michael A. Rawlins, Associate Director, Climate System Research Center, UMass AmherstLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1946422022-11-17T11:51:29Z2022-11-17T11:51:29ZAfrican mountains are feeling the heat of climate change<figure><img src="https://images.theconversation.com/files/495306/original/file-20221115-23-c6fqra.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Mount Kenya</span> <span class="attribution"><span class="source">WanderingNomad / Getty IMages</span></span></figcaption></figure><p>Mountains are special places. They have distinctive climates that are generally cooler and wetter than surrounding lowlands, and they host plants, animals and landscapes that are uniquely found in these environments. However, mountains are under threat because of climate change, and this has an impact on every single property of mountains, including their climate, weathering and erosion processes, soils, ecosystems, water resources, geological hazards, regional economies, and cultural practices. </p>
<p>My <a href="https://peerj.com/articles/14253/">work</a> on the impacts of ongoing climate change in mountains highlights the sensitivity of mountain properties and processes to changes in temperature and precipitation – mainly expressed in mountains as snowfall. However, there is less understanding of mountain systems in Africa compared to other mountains globally. This article therefore focuses on mountain properties in Africa, why these are particularly sensitive to climate change, and why this is important.</p>
<h2>Ice and snow</h2>
<p>One key property of mountains worldwide is that they are often covered by snow and ice (glaciers). This reflects moist air and cold temperatures over mountain summits. Not only do snow and ice present unique habitats for plant and animal species, they also have a vital role in the regional climate systems of mountains. Snow and ice tend to be light in colour, so they reflect sunlight back out to space, keeping the land surface cold. This is called the <a href="https://scied.ucar.edu/learning-zone/how-climate-works/albedo-and-climate">albedo effect</a>. </p>
<p>However, if snowfall does not take place or the snow melts away, the mountain land surface remains dark. This means it absorbs rather than reflects the sun’s energy, making the surface warmer. This can cause more snowmelt, exposing more dark rocks, with more heating and melting. </p>
<p>The outcome of this process is that changing patterns of snowfall have big implications for mountain heat budgets. Mountains worldwide are already <a href="https://iccinet.org/statecryo22/">warming twice as fast</a> as the global average. This makes them particularly sensitive to climate change. </p>
<p>African mountains are not immune to climate change. Small glaciers still exist in three mountain massifs – Mount Kenya (Kenya), Kilimanjaro (Tanzania) and the Rwenzori mountains (Uganda) – but these are in <a href="https://wgms.ch/">rapid retreat</a>. They are also predicted to <a href="https://unesdoc.unesco.org/ark:/48223/pf0000383551">disappear entirely</a> by the middle of the century. Snowfall is also highly variable, such as over the <a href="https://earthobservatory.nasa.gov/images/88509/lesotho-sees-its-heaviest-snowfall-in-two-decades">Maloti-Drakensberg mountains</a> of southern Africa.</p>
<p>The full implications of this loss of ice and snow, and of climate change in African mountains more generally, have not been fully considered. Ice retreat in other deglacierising mountains worldwide leads to a substantial increase in hazards of different types, including rockfalls, landslides and debris flows. These hazards can also take place thousands of years after initial ice retreat. </p>
<p>This may mean that, even though the glaciers that exist in Africa today are very small, any resulting hazards could potentially be large and unpredictable in their timing and location. These are potentially future issues in African mountains. </p>
<p>Another important factor is how snow and ice melt across African mountains will affect their wider landscapes. Snow and ice often serve as water sources to surrounding communities, especially in locations that are water scarce, which includes East Africa. Water availability in the environment influences soils, ecosystems, river processes and the potential for flood and landslide hazards. </p>
<p>The presence of snow and ice therefore has wider environmental significance across mountain landscapes, and in ways that are not fully understood. </p>
<h2>Other important roles</h2>
<p>African mountains are also important for other reasons. For example, they host the Afromontane biogeographical region, a global <a href="https://www.cepf.net/our-work/biodiversity-hotspots/hotspots-defined">biodiversity hotspot</a> of endemic podocarp (conifer) forest species that extends as a corridor through upland areas of southern and eastern Africa. </p>
<p>Above the treeline, alpine pastures provide grazing land for herders, a key socioeconomic and cultural activity in remote mountains in Africa. </p>
<p>Summer and winter tourism – whether in South Africa or Morocco – is also linked closely to mountain landscapes, snow, water and the presence of endemic species. </p>
<p>All of these activities are under threat because of climate change. Mountain ecosystems are critically linked to temperature and precipitation conditions. Climate change may therefore pose problems for both the survival of keystone species and for overall biome integrity, especially where they are encroached by invasive species, agriculture and forestry. These changes also have secondary effects on ecosystem services, food, fuel and carbon storage. </p>
<p>Thus, mountains have a wide range of properties that are linked to climate, and a key question is how mountain systems as a whole will respond to climate change over future decades.</p>
<h2>Mountain communities</h2>
<p>Sustainable development of <a href="https://www.ipcc.ch/report/ar6/wg2/downloads/report/IPCC_AR6_WGII_CCP5.pdf">mountain communities</a>, where human activity responds to the changing nature of mountain systems, is a key strategy for minimising the impacts of climate change, both in mountains and in surrounding areas. </p>
<p>This can be done by monitoring and treating sources of hazard risk as a result of melting snow and ice, building resilient infrastructure and community resilience, and protecting mountains as sites of geological, ecological and cultural heritage. These actions can help limit climate change impacts on sensitive mountains in Africa and elsewhere.</p><img src="https://counter.theconversation.com/content/194642/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jasper Knight does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Mountain systems are sensitive to climate change. Loss of snow and ice sets off effects which have wide ranging consequences.Jasper Knight, Professor of Physical Geography, University of the WitwatersrandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1916512022-10-17T17:38:56Z2022-10-17T17:38:56ZSnow can spread and worsen the effects of pollutants in the environment<figure><img src="https://images.theconversation.com/files/488312/original/file-20221005-25-3ul0kh.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C5068%2C3368&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Snow's physical properties mean that it can accumulate chemicals from the environment, including nanoparticles from car exhaust.</span> <span class="attribution"><span class="source">(Shutterstock)</span></span></figcaption></figure><iframe style="width: 100%; height: 100px; border: none; position: relative; z-index: 1;" allowtransparency="" allow="clipboard-read; clipboard-write" src="https://narrations.ad-auris.com/widget/the-conversation-canada/snow-can-spread-and-worsen-the-effects-of-pollutants-in-the-environment" width="100%" height="400"></iframe>
<p>By October, autumn’s arrival brings with it the promise of winter — and snow. </p>
<p>And with it comes a quieter world, thanks to snow’s ability to absorb noise. This is because the spaces between snow crystals limit sound waves from bouncing around, creating a soundproofing effect. </p>
<p>Snow also adsorbs other matters it comes into contact with. Adsorption is when substances adhere on surfaces of materials (usually liquids or solids). The adsorptive properties of snow are the reason for some of its unique features, including its loosely bound crystalline porous structure with finely divided individually shaped flakes with large surface areas. </p>
<p>Its dynamic changes between ice and liquid states facilitate the absorption and release of pollutants, depending on prevailing surface and atmospheric conditions. </p>
<p>As an analytical material chemist with a research background in adsorption, I am interested in understanding how various materials — like snow — adsorb certain substances, like persistent organic and vehicular exhaust pollutants.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="a pile of dirty snow at a street corner" src="https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489891/original/file-20221016-22-qbrsr0.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">During winter, piles of snow like this one become a regular sight.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Snow and pollution</h2>
<p>In the winter, snow becomes a superabsorbent for a wide range of <a href="https://doi.org/10.1016/j.scitotenv.2020.144136">pollutants</a>, including vehicular exhaust particulate matters, <a href="https://doi.org/10.1016/j.microc.2014.10.010">persistent organic pollutants</a> (POPs), trace metals and <a href="https://doi.org/10.1016/j.watres.2021.117493">chlorides from road salts</a>. </p>
<p>As snow subsequently moves around or melts, most of these pollutants find their way into underground pipes and aquifers. </p>
<p>POPs are some of the most dangerous pollutants because they remain active, lasting for several years within their environments before <a href="https://doi.org/10.1016/j.rsma.2022.102688">finally degrading into other chemical forms</a>. POPs, such as polychlorinated biphenyls, organochlorine pesticides and perflouroalkylated substances, have <a href="https://www.epa.gov/international-cooperation/persistent-organic-pollutants-global-issue-global-response">severe environmental impacts</a>. </p>
<p>They are classified under the <a href="https://www.canada.ca/en/environment-climate-change/services/canadian-environmental-protection-act-registry/historical/plans-policies/statement-pops-negotiations/backgrounder-persistent-organic-pollutants.html">Toxic Substances Management Policy as Track 1 substances in Canada, and are usually targeted for environmental removal</a>. </p>
<p>Just like POPs, very little is also known about how chemical pollutants from the exhausts of gasoline-powered vehicles interact with snow. </p>
<p>In Canadian cities, snow is moved around through various means, including snow melts, during plowing, on tires of vehicles or even soles of pedestrian shoes. During transportation, changes in ground surface pressure and ambient temperature can also affect the adsorption rates of chemical pollutants on snow. </p>
<p>Research conducted in Québec has shown that snow adsorbs significant amounts of organic pollutants and aerosol particles from exhaust pipes <a href="https://doi.org/10.1016/j.envpol.2017.01.082">within 30 minutes of exposure</a>. These researchers also observed the adsorption of aerosol particles with larger particulate sizes (approximately 50-400 nm) relative to smaller nanoparticles (less than 50 nm).</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="cars follow behind three snowplows on a highway" src="https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/489886/original/file-20221016-56148-cmyp4e.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Snow carrying pollutants from road salts and vehicle exhausts can make its way into water systems.</span>
<span class="attribution"><span class="source">(Shutterstock)</span></span>
</figcaption>
</figure>
<h2>Health effects</h2>
<p>POPs are introduced into the environment through agricultural and industrial practices. Most of them may have come from other anthropogenic sources but are unintentionally released from simple events like <a href="https://nepis.epa.gov/Exe/ZyPDF.cgi/70000AZL.PDF?Dockey=70000AZL.PDF">burning household waste</a>. </p>
<p>Burning industrial, municipal or medical wastes can also release dioxins and furans. <a href="https://www.atsdr.cdc.gov/ToxProfiles/tp94-c6.pdf">Toxaphene</a> and <a href="https://www.atsdr.cdc.gov/ToxProfiles/tp90-c6.pdf">hexachlorobenzene</a> could originate from uncontrolled insecticide and pesticide waste disposal. Upon exposure during winter, these chemical pollutants find their way into the snow, then into surface water and up the food chain. They can adversely affect aquatic life when subsequently introduced into the aquatic ecosystems. </p>
<p>POPs and exhaust particulate matters can <a href="https://www.epa.gov/international-cooperation/persistent-organic-pollutants-global-issue-global-response">affect human health</a>. They can cause allergies, hypersensitivity, birth defects and neurological disorders. Most POPs are carcinogens. Some of them may alter the nervous systems, leading to chronic health conditions. POPs can also affect reproductive health and disrupt the immune system. Some particulate matters cause lung inflammation and increase the risk of blood clotting. </p>
<p>These severe impacts on human health and environment sustainability are why POPs are <a href="https://www.canada.ca/en/environment-climate-change/corporate/international-affairs/partnerships-organizations/persistent-organic-pollutants-stockholm-convention.html">currently regulated under the Stockholm Convention, as adopted by Canada in 2001</a>. </p>
<p>Between applicable industries and environmental monitoring agencies, federal and provincial governments and us, everyone has a part to play. All hands must be on deck in providing sustainable regulations for these pollutants. And as we approach winter, measures should be developed to reduce the amount of pollutants that can accumulate and persist in snow.</p><img src="https://counter.theconversation.com/content/191651/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Eduok, U. does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>From persistent chemicals to exhaust particulate matter, snow accumulates highly toxic pollutants. Regulations are needed to address the impacts on water supplies and the food chain.Eduok, U., Senior Research Associate, Chemistry, Western UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1853642022-07-05T12:14:47Z2022-07-05T12:14:47ZClimate change is making flooding worse: 3 reasons the world is seeing more record-breaking deluges and flash floods<figure><img src="https://images.theconversation.com/files/471429/original/file-20220628-14613-2mjpl2.jpg?ixlib=rb-1.1.0&rect=0%2C37%2C3134%2C2056&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Fast-moving floodwater obliterated sections of major roads through Yellowstone National Park in 2022.</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/yellowstonenps/52167350392">Jacob W. Frank/National Park Service</a></span></figcaption></figure><p>Heavy rain combined with melting snow can be a destructive combination. </p>
<p>In June 2022, storms dumped up to 5 inches of rain over three days in the mountains in and around Yellowstone National Park, rapidly melting snowpack. As the rain and meltwater poured into creeks and then rivers, it became a flood that damaged roads, cabins and utilities and <a href="https://apnews.com/article/floods-travel-montana-obituaries-evacuations-3753caa39435d9f3f45d8b582381a0c6">forced more than 10,000 people to evacuate</a>.</p>
<p>The Yellowstone River shattered its previous record and reached its highest water levels recorded since monitoring began almost 100 years ago.</p>
<p>Although floods are a natural occurrence, human-caused climate change is <a href="https://www.gyclimate.org/">making severe flooding events like these more common</a>. I study how climate change affects hydrology and flooding. In mountainous regions, three effects of climate change in particular are creating higher flood risks: more intense precipitation, shifting snow and rain patterns and the effects of wildfires on the landscape.</p>
<h2>Warmer air leads to more intense precipitation</h2>
<p>One effect of climate change is that a <a href="https://www.epa.gov/climate-indicators/climate-change-indicators-heavy-precipitation">warmer atmosphere creates more intense precipitation events</a>. </p>
<p>This occurs because warmer air can hold more moisture. The amount of water vapor that the atmosphere can contain increases by <a href="https://doi.org/10.1038/nclimate1452">about 7% for every 1.8 degrees Fahrenheit</a> (1 degree Celsius) of increase in atmospheric temperature.</p>
<p>Research has documented that this <a href="https://doi.org/10.1029/2018WR024067">increase in extreme precipitation is already occurring</a>, not only in regions like Yellowstone, but <a href="https://theconversation.com/global-evidence-links-rise-in-extreme-precipitation-to-human-driven-climate-change-163715">around the globe</a>. The fact that the world has experienced multiple record flooding events in recent years – including catastrophic <a href="https://www.bbc.com/news/world-australia-61991112">flooding in</a> <a href="http://www.bom.gov.au/climate/enso/wrap-up/archive/20220705.archive.shtml">Australia</a>, <a href="https://www.science.org/content/article/europe-s-deadly-floods-leave-scientists-stunned">Western Europe</a> <a href="https://weather.com/en-IN/india/monsoon/news/2022-07-12-around-1k-rescued-from-gujarat-floods-heavy-rains-to-continue">India</a> and <a href="https://www.washingtonpost.com/weather/2021/07/21/zhengzhou-china-record-rain-flooding/">China</a> – is not a coincidence. Climate change is making record-breaking extreme precipitation more likely.</p>
<figure class="align-center ">
<img alt="A woman with work gloves and clothing covered in mud walks through a muddy residential street filled with mud-covered furniture and other damaged belongings people are throwing out after a flood." src="https://images.theconversation.com/files/471466/original/file-20220628-16342-auzmdw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/471466/original/file-20220628-16342-auzmdw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/471466/original/file-20220628-16342-auzmdw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/471466/original/file-20220628-16342-auzmdw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/471466/original/file-20220628-16342-auzmdw.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=502&fit=crop&dpr=1 754w, https://images.theconversation.com/files/471466/original/file-20220628-16342-auzmdw.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=502&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/471466/original/file-20220628-16342-auzmdw.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=502&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Extreme rain storms triggered flooding and mudslides in Western Europe in July 2021, killing more than 200 people.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/volunteers-and-residents-start-the-clean-up-process-at-news-photo/1329350141?adppopup=true">Thomas Lohnes/Getty Images</a></span>
</figcaption>
</figure>
<p><iframe id="zBAAz" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/zBAAz/5/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>The latest <a href="https://www.ipcc.ch/report/sixth-assessment-report-working-group-i/">assessment report</a> published by the Intergovernmental Panel on Climate Change shows how this pattern will continue in the future as global temperatures continue to rise.</p>
<h2>More precipitation falling as rain</h2>
<p>In colder areas, especially mountainous or high-latitude regions, climate change affects flooding in additional ways. </p>
<p>In these regions, many of the largest historical <a href="https://doi.org/10.1002/2016GL068070">floods have been caused by snowmelt</a>. However, with warmer winters due to climate change, <a href="https://www.climatecentral.org/news/winters-becoming-more-rainy-across-us-20017">less winter precipitation is falling as snow</a>, and more is falling as rain instead.</p>
<p>This shift from snow to rain can have dramatic implications for flooding. While snow typically melts slowly in the late spring or summer, rain creates runoff that flows to rivers more quickly. As a result, research has shown that <a href="https://doi.org/10.1029/2022GL098855">rain-caused floods can be much larger than snowmelt-only floods</a>, and that the shift from snow to rain <a href="https://doi.org/10.1029/2019WR025571">increases overall flood risk</a>.</p>
<p>The transition from snow to rain is already occurring, <a href="https://theconversation.com/yellowstone-is-losing-its-snow-as-the-climate-warms-and-that-means-widespread-problems-for-water-and-wildlife-163223">including in places like Yellowstone National Park</a>. Scientists have also found that <a href="https://doi.org/10.1002/2015WR017784">rain-caused floods are becoming more common</a>. In some locations, the changes in flood risk due to the shift from snow to rain could even be larger than the effect from increased precipitation intensity.</p>
<p><iframe id="O1p7r" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/O1p7r/5/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>Changing patterns of rain on snow</h2>
<p>When <a href="https://doi.org/10.1175/BAMS-88-3-319">rain falls on snow</a>, as happened in the recent flooding in Yellowstone, the combination of rain and snowmelt can lead to especially high runoff and flooding.</p>
<p>In some cases, rain-on-snow events occur while the ground is still partially frozen. Soil that is frozen or already saturated can’t absorb additional water, so even more of the rain and snowmelt run off, contributing directly to flooding. This combination of rain, snowmelt and frozen soils was a primary driver of the <a href="https://www.nytimes.com/2019/03/18/us/nebraska-flooding-facts.html">Midwest flooding in March 2019</a> that caused over US$12 billion in damage.</p>
<p>While rain-on-snow events are not a new phenomenon, climate change can shift when and where they occur. Under warmer conditions, <a href="https://doi.org/10.1038/s41558-018-0236-4">rain-on-snow events become more common at high elevations</a>, where they were previously rare. Because of the increases in rainfall intensity and warmer conditions that lead to rapid snowmelt, there is also the possibility of larger rain-on-snow events than these areas have experienced in the past.</p>
<figure class="align-center ">
<img alt="A large two-story building is collapsing after fast-moving water eroded the land under nearly half of it." src="https://images.theconversation.com/files/471431/original/file-20220628-14648-yhqe7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/471431/original/file-20220628-14648-yhqe7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/471431/original/file-20220628-14648-yhqe7t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/471431/original/file-20220628-14648-yhqe7t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/471431/original/file-20220628-14648-yhqe7t.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/471431/original/file-20220628-14648-yhqe7t.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/471431/original/file-20220628-14648-yhqe7t.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The 2022 Yellowstone flood inundated communities and swiftly eroded the land beneath this cabin that housed park employees.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/yellowstonenps/52146801150">Gina Riquier via National Park Service</a></span>
</figcaption>
</figure>
<p>In lower-elevation regions, rain-on-snow events may actually become less likely than they have been in the past because of the decrease in snow cover. These areas could still see worsening flood risk, though, because of the increase in heavy downpours.</p>
<h2>Compounding effects of wildfire and flooding</h2>
<p>Changes in flooding are not happening in isolation. Climate change is also exacerbating <a href="https://www.nationalgeographic.com/science/article/climate-change-increases-risk-fires-western-us">wildfires</a>, creating another risk during rainstorms: mudslides. </p>
<p>Burned areas are more <a href="https://doi.org/10.1029/2020EF001735">susceptible to mudslides and debris flows during extreme rain</a>, both because of the lack of vegetation and changes to the soil caused by the fire. In 2018 in Southern California, heavy rain within the boundary of the <a href="https://www.cnn.com/2018/06/02/us/thomas-fire-officially-out/index.html">2017 Thomas Fire</a> caused <a href="https://www.cnn.com/2018/01/11/us/mudslide-slider-california/index.html">major mudslides</a> that destroyed over 100 homes and led to more than 20 deaths. Fire can change the soil in ways that allow <a href="https://doi.org/10.2113/EEG-D-20-00029">less rain to infiltrate into the soil</a>, so more rain ends up in streams and rivers, leading to worse flood conditions.</p>
<figure class="align-center ">
<img alt="Two men point stand on a deck overlooking a neighboring house where mud has flowed through the yard and is mounded half way up the side of the home." src="https://images.theconversation.com/files/471467/original/file-20220628-14559-d6mcuz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/471467/original/file-20220628-14559-d6mcuz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/471467/original/file-20220628-14559-d6mcuz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/471467/original/file-20220628-14559-d6mcuz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/471467/original/file-20220628-14559-d6mcuz.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/471467/original/file-20220628-14559-d6mcuz.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/471467/original/file-20220628-14559-d6mcuz.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A 2021 rainstorm that hit the denuded landscape of a burn scar sent mud flowing into streets and yards in Silverado, California.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/two-men-survey-the-damage-from-mud-and-debris-that-ran-news-photo/1299356465">Paul Bersebach/MediaNews Group/Orange County Register via Getty Images</a></span>
</figcaption>
</figure>
<p>With the uptick in wildfires due to climate change, more and more areas are exposed to these risks. This combination of wildfires followed by extreme rain will also become <a href="https://doi.org/10.1126/sciadv.abm0320">more frequent in a future with more warming</a>.</p>
<p>Global warming is creating complex changes in our environment, and there is a clear picture that it increases flood risk. As the Yellowstone area and other flood-damaged mountain communities rebuild, they will have to find ways to adapt for a riskier future.</p><img src="https://counter.theconversation.com/content/185364/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Frances Davenport does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Extreme downpours brought deadly flooding to the Appalachian region, just a few weeks after the destructive Yellowstone River flood.Frances Davenport, Assistant Professor of Civil and Environmental Engineering, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1772332022-03-16T12:34:02Z2022-03-16T12:34:02ZCloud seeding might not be as promising as drought-troubled states hope<figure><img src="https://images.theconversation.com/files/446845/original/file-20220216-25-1vorff5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Cloud seeding equipment near Winter Park in Colorado.</span> <span class="attribution"><a class="source" href="https://www.denverwater.org/tap/cloud-seedings-role-winter-season">Denver Water</a></span></figcaption></figure><p>On mountain peaks scattered across Colorado, <a href="https://cwcb.colorado.gov/focus-areas/supply/weather-modification-program">machines are set up to fire chemicals into the clouds</a> in attempts to generate snow. The process is called cloud seeding, and as global temperatures rise, more <a href="https://public.wmo.int/en/resources/bulletin/seeding-change-weather-modification-globally">countries</a> and <a href="https://www.theguardian.com/environment/2021/mar/23/us-stated-cloud-seeding-weather-modification">drought-troubled states</a> are using it in sometimes desperate efforts to modify the weather.</p>
<p>But cloud seeding isn’t as simple as it sounds, and it might not be as promising as people wish.</p>
<hr>
<iframe id="noa-web-audio-player" style="border: none" src="https://embed-player.newsoveraudio.com/v4?key=x84olp&id=https://theconversation.com/cloud-seeding-might-not-be-as-promising-as-drought-troubled-states-hope-177233&bgColor=F5F5F5&color=D8352A&playColor=D8352A" width="100%" height="110px"></iframe>
<p><em>You can listen to more articles from The Conversation, narrated by Noa, <a href="https://theconversation.com/us/topics/audio-narrated-99682">here</a>.</em></p>
<hr>
<p>As an <a href="https://www.researchgate.net/scientific-contributions/William-R-Cotton-72102078">atmospheric scientist</a>, I have studied and <a href="https://www.cambridge.org/core/books/abs/human-impacts-on-weather-and-climate/rise-of-the-science-of-weather-modification-by-cloud-seeding/973C1181FD0E4220848FC83AFE05D2D2">written about weather modification</a> for 50 years. Cloud seeding <a href="https://doi.org/10.1073/pnas.1917204117">experiments that produce snow or rain</a> require the <a href="https://doi.org/10.1175/JAMC-D-18-0341.1">right kind of clouds</a> with enough moisture, and the right temperature and wind conditions. The percentage increases in precipitation are small, and it’s difficult to tell when snow or rain fell naturally and when it was triggered by seeding.</p>
<h2>How modern cloud seeding began</h2>
<p>The modern age of weather modification began in the 1940s in Schenectady, New York. </p>
<p>Vince Schaefer, a scientist working for General Electric, <a href="https://patentimages.storage.googleapis.com/7f/03/d4/b4e0d609dd15ee/US2570867.pdf">discovered that adding small pellets of dry ice</a> to a freezer containing “<a href="https://www.pnnl.gov/news-media/supercooled-water-stable-liquid-scientists-show-first-time">supercooled</a>” water droplets triggered a proliferation of ice crystals. </p>
<p><a href="https://rammb.cira.colostate.edu/wmovl/vrl/tutorials/euromet/courses/glossary/bergeron.htm">Other scientists had theorized</a> that the right mix of supercooled water drops and ice crystals could cause precipitation. <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/snow/how-does-snow-form">Snow forms</a> when ice crystals in clouds stick together. If ice-forming particles could be added to clouds, the scientists reasoned, moisture that would otherwise evaporate might have a greater chance of falling. Schaefer proved it could work.</p>
<p>On Nov. 13, 1946, Schaefer <a href="https://archive.org/stream/historyofproject00have/historyofproject00have_djvu.txt">dropped crushed dry ice</a> from a plane into supercooled stratus clouds. “I looked toward the rear and was thrilled to see long streamers of snow falling from the base of the cloud through which we had just passed,” <a href="https://archive.org/stream/historyofproject00have/historyofproject00have_djvu.txt">he wrote in his journal</a>. A few days later, he wrote that trying the same technique appeared to have improved visibility in fog.</p>
<figure class="align-center ">
<img alt="A man looks into a freezer looking amazed at what he sees." src="https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=827&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=827&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=827&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1040&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1040&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446705/original/file-20220216-3223-1u7dpe1.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1040&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Vincent Schaefer, in foreground, examines snow created in a modified GE freezer in 1947, with Irving Langmuir, at left, and Bernard Vonnegut.</span>
<span class="attribution"><a class="source" href="https://nyheritage.contentdm.oclc.org/digital/collection/p16694coll20/id/5747/rec/33">General Electric Company/Museum of Science and Innovation</a></span>
</figcaption>
</figure>
<p>A colleague at GE, Bernie Vonnegut, searched through chemical tables for materials with a crystallographic structure similar to ice and discovered that <a href="https://doi.org/10.1063/1.1697813">a smoke of silver iodide particles</a> could have the same effect at temperatures below -20 C (-4 F) as dry ice.</p>
<p>Their research led to <a href="https://archive.org/stream/historyofproject00have/historyofproject00have_djvu.txt">Project Cirrus</a>, a joint civilian-military program that explored seeding a variety of clouds, including supercooled stratus clouds, cumulus clouds and <a href="https://vlab.noaa.gov/web/nws-heritage/-/almost-science-fiction-hurricane-modification-and-project-stormfury">even hurricanes</a>. Within a few years, communities and companies that rely on water were spending US$3 million to $5 million a year on cloud-seeding projects, particularly in the drought-troubled western U.S., <a href="https://www.nsf.gov/nsb/publications/1965/nsb1265.pdf">according to congressional testimony in the early 1950s</a>.</p>
<h2>But does cloud seeding actually work?</h2>
<p>The results of about 70 years of research into the effectiveness of cloud seeding are mixed.</p>
<p>Most scientific studies aimed at evaluating the effects of seeding cumulus clouds have shown little to no effect. However, the results of seeding wintertime <a href="https://cloudatlas.wmo.int/en/orographic-influences-on-clouds.html">orographic clouds</a> – clouds that form as air rises over a mountain – have <a href="https://doi.org/10.1073/pnas.1917204117">shown increases in precipitation</a>.</p>
<p>There are two basic approaches to cloud seeding. One is to seed supercooled clouds with silver iodide or dry ice, causing ice crystals to grow, consume moisture from the cloud and fall as snow or rain. It might be shot into the clouds in rockets or sprayed from an airplane or mountaintop. The second involves warm clouds and <a href="https://www.nytimes.com/2003/09/02/science/q-a-salt-and-humidity.html">hygroscopic</a> materials like salt particles. These particles take on water vapor, becoming larger to fall faster.</p>
<figure class="align-center ">
<img alt="A drawing of a plane flying" src="https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=906&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=906&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=906&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1139&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1139&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446703/original/file-20220216-28-1gyqh5x.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1139&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">An illustration of cloud-seeding processes.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Cloud_seeding#/media/File:Cloudseedingimagecorrected.jpg">Naomi E. Tesla/Wikipedia</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>The amount of snow or rain tied to cloud seeding has varied, with <a href="https://public.wmo.int/en/resources/bulletin/seeding-change-weather-modification-globally">up to 14% reported in experiments in Australia</a>. In the U.S., studies have found a few percentage points of increase in precipitation. In a 2020 study, scientists <a href="https://doi.org/10.1073/pnas.1917204117">used radar to watch as 20 minutes of cloud seeding</a> caused moisture inside clouds to thicken and fall. In all, about one-tenth of a millimeter of snow accumulated on the ground below in a little over an hour.</p>
<p>Another study, in 2015, used climate data and a <a href="https://doi.org/10.1175/JAMC-D-17-0335.1">six-year cloud-seeding experiment</a> in the mountains of Wyoming to estimate that <a href="https://doi.org/10.1175/JAMC-D-14-0163.1">conditions there were right</a> for cloud seeding about a quarter of the time from November to April. But the results likely would increase the snowpack by <a href="https://doi.org/10.1175/JAMC-D-18-0341.1">no more than about 1.5%</a> for the season.</p>
<p>While encouraging, these experiments have by no means reached the level of significance that Schaefer and his colleagues had anticipated.</p>
<h2>Weather modification is gaining interest again</h2>
<p><a href="https://doi.org/10.1175/JAMC-D-18-0341.1">Scientists today are continuing to carry out randomized seeding experiments</a> to determine when cloud seeding enhances precipitation and by how much.</p>
<p>People have raised a few concerns about negative effects from cloud seeding, but those effects appear to be minor. Silver ion is a <a href="https://doi.org/10.1029/WR006i001p00088">toxic heavy metal</a>, but the amount of silver iodide in seeded snowpack is so small that extremely sensitive instrumentation must be used to detect its presence. </p>
<figure class="align-center ">
<img alt="A man attaches a row of canisters to an airplane wing." src="https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&rect=5%2C5%2C3637%2C2419&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/446701/original/file-20220216-27-1tukw0v.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Several companies attempt cloud seeding from airplanes.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/DroughtCloudSeeding/afa3c57641344d3f9165eedf834b388e/photo">AP Photo/Dave Kolpack</a></span>
</figcaption>
</figure>
<p>Meanwhile, extreme weather and droughts are increasing interest in weather modification. </p>
<p>The World Meteorological Organization reported in 2017 that weather modification programs, including suppressing crop-damaging hail and increasing rain and snowfall, were underway in <a href="https://public.wmo.int/en/resources/bulletin/seeding-change-weather-modification-globally">more than 50 countries</a>. My home state of Colorado has <a href="https://cwcb.colorado.gov/weather-modification-grant-program">supported cloud-seeding operations</a> for years. Regardless of the mixed evidence, many communities are counting on it to work.</p><img src="https://counter.theconversation.com/content/177233/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>William R. Cotton does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p>Several states are experimenting with weather modification to try to generate snow as water supplies shrink. An atmospheric scientist explains the history behind it – and the challenges.William R. Cotton, Professor Emeritus of Meteorology, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.