tag:theconversation.com,2011:/ca/topics/sierra-nevada-18876/articlesSierra Nevada – The Conversation2024-01-04T13:48:42Ztag: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/2011562023-03-16T12:50:59Z2023-03-16T12:50:59ZIs the Western drought finally ending? That depends on where you look<figure><img src="https://images.theconversation.com/files/514982/original/file-20230313-16-kn6nns.jpg?ixlib=rb-1.1.0&rect=0%2C8%2C6000%2C3979&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">California's snowpack was more than twice the average in much of the state in early March 2023.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/vehicles-pass-along-a-highway-snowplowed-through-deep-snow-news-photo/1458394332">Mario Tama/Getty Images</a></span></figcaption></figure><p>After three years of extreme drought, the Western U.S. is finally getting a break. Mountain ranges are <a href="https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd1045012.html">covered in deep snow</a>, and water reservoirs in many areas <a href="https://cdec.water.ca.gov/resapp/RescondMain">are filling up</a> following a series of <a href="https://www.noaa.gov/stories/what-are-atmospheric-rivers">atmospheric rivers</a> that brought record rain and snowfall to large parts of the region.</p>
<p>Many people are looking at the snow and water levels and asking: Is the drought finally over?</p>
<p>There is a lot of nuance to the answer. Where you are in the West and how you define “drought” make a difference. As a <a href="https://scholar.google.com/citations?user=dloXR6MAAAAJ&hl=en">drought and water researcher</a> at the <a href="https://www.dri.edu/directory/dan-mcevoy/">Desert Research Institute’s</a> Western Regional Climate Center, here’s what I’m seeing.</p>
<h2>How fast each region recovers will vary</h2>
<p>The winter of 2023 has made a big dent in improving the drought and potentially eliminating the water shortage problems of the last few summers. </p>
<p>I say “potentially” because in many areas, a lot of the impacts of drought tend to <a href="https://iopscience.iop.org/article/10.1088/1748-9326/aca8bd/meta">show up in summer</a>, once the winter rain and snow stop and the West starts relying on reservoirs and streams for water. <a href="https://doi.org/10.1088/1748-9326/aca8bd">Spring heat waves</a> like the ones we saw in 2021 or <a href="https://www.wpc.ncep.noaa.gov/metwatch/metwatch_mpd_multi.php?md=0093&yr=2023">rain in the mountains</a> could melt the snowpack faster than normal.</p>
<figure class="align-center ">
<img alt="A US map shows heavy rain across much of California, Nevada, Utah, Colorado, Wyoming, Nebraska and Arizona" src="https://images.theconversation.com/files/515502/original/file-20230315-28-wlk89n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515502/original/file-20230315-28-wlk89n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=453&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515502/original/file-20230315-28-wlk89n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=453&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515502/original/file-20230315-28-wlk89n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=453&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515502/original/file-20230315-28-wlk89n.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=569&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515502/original/file-20230315-28-wlk89n.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=569&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515502/original/file-20230315-28-wlk89n.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=569&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 in January brought heavy rain across large parts of the West. Another powerful storm system hit in March.</span>
<span class="attribution"><a class="source" href="https://www.climate.gov/news-features/event-tracker/atmospheric-rivers-take-chunk-out-california-drought">Climate.gov</a></span>
</figcaption>
</figure>
<h2>California and the Great Basin</h2>
<p>In California, the state’s three-year precipitation deficit was <a href="https://www.climate.gov/news-features/event-tracker/atmospheric-rivers-take-chunk-out-california-drought">just about erased by the atmospheric rivers</a> that caused so much flooding in December and January. By March, the snowpack across the Sierra Nevada was <a href="https://cdec.water.ca.gov/reportapp/javareports?name=PLOT_SWC">well above the historical averages</a> – and <a href="https://www.drought.gov/topics/snow-drought">more than 200%</a> of average in some areas. The Metropolitan Water District of Southern California announced it was <a href="https://www.mwdh2o.com/press-releases/metropolitan-board-rescinds-emergency-conservation-mandate-imposed-on-dozens-of-communities">ending emergency water restrictions</a> for nearly 7 million people on March 15.</p>
<p>It seems as though most of the surface water drought – drought involving streams and reservoirs – could be eliminated by summer in California and the Great Basin, across Nevada and western Utah. </p>
<figure class="align-center ">
<img alt="Two images of Lake Oroville, from November 2022 to late January 2023 show a sharp decline in water levels and a wide ring around the edge." src="https://images.theconversation.com/files/515503/original/file-20230315-352-zcwyhd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/515503/original/file-20230315-352-zcwyhd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/515503/original/file-20230315-352-zcwyhd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/515503/original/file-20230315-352-zcwyhd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/515503/original/file-20230315-352-zcwyhd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/515503/original/file-20230315-352-zcwyhd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/515503/original/file-20230315-352-zcwyhd.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 early 2023 storms likely could have filled Lake Oroville, one of California’s largest reservoirs. But reservoirs are also essential for flood management, so managers balance how much water to retain and how much to release.</span>
<span class="attribution"><a class="source" href="https://earthobservatory.nasa.gov/images/150953/reservoirs-rise-but-groundwater-woes-remain">NASA Earth Observatory images by Lauren Dauphin</a></span>
</figcaption>
</figure>
<p>But that’s only surface water. Drought also affects groundwater, and those effects will <a href="https://doi.org/10.1016/j.jhydrol.2021.126917">take longer to alleviate</a>.</p>
<p>Studies in California have shown that, even after wet years like 2017 and 2019, the groundwater systems <a href="https://doi.org/10.1029/2021WR030352">did not fully recover</a> from the previous drought, in part because of years of overpumping groundwater for agriculture, and the aquifers were <a href="https://doi.org/10.1038/s41467-022-35582-x">not fully recharging</a>.</p>
<p>In that sense, the drought is not over. But at the broader scale for the region, a lot of the drought impacts that people experience will be lessened or almost gone by this summer. </p>
<h2>The Colorado River Basin</h2>
<p>Similar to the Sierra Nevada, the Upper Colorado River Basin – Wyoming, Colorado, Utah and northwestern New Mexico – has a healthy snowpack this year, and it’s looking like a very good water year there. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/516972/original/file-20230322-24-pk37ff.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map showing highest snow water equivalent in California, the Great Basin and Arizona" src="https://images.theconversation.com/files/516972/original/file-20230322-24-pk37ff.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/516972/original/file-20230322-24-pk37ff.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=775&fit=crop&dpr=1 600w, https://images.theconversation.com/files/516972/original/file-20230322-24-pk37ff.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=775&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/516972/original/file-20230322-24-pk37ff.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=775&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/516972/original/file-20230322-24-pk37ff.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=973&fit=crop&dpr=1 754w, https://images.theconversation.com/files/516972/original/file-20230322-24-pk37ff.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=973&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/516972/original/file-20230322-24-pk37ff.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=973&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 snow water equivalent, a measure of snowpack, was over 200% of average in several areas on March 21, 2023.</span>
<span class="attribution"><a class="source" href="https://www.drought.gov/topics/snow-drought">Drought.gov</a></span>
</figcaption>
</figure>
<p>But one single good water year is not going to fill <a href="https://earthobservatory.nasa.gov/images/150111/lake-mead-keeps-dropping">Lake Mead</a> and <a href="https://earthobservatory.nasa.gov/images/150249/lake-powell-still-shrinking">Lake Powell</a>. Most of the region relies on those two reservoirs, which <a href="https://theconversation.com/what-is-dead-pool-a-water-expert-explains-182495">have declined to worrying levels</a> over the past two decades.</p>
<p>Two good water years won’t do it either. Over the next decade, most years will have to be above average to begin to fill those giant reservoirs. <a href="https://www.scientificamerican.com/article/colorado-river-is-in-danger-of-a-parched-future/">Rising temperatures and drying</a> will make that even harder. </p>
<p>So, that system is still going to be dealing with a lot of the same long-term drought impacts that it has been seeing. The reservoirs will likely rise some, but nowhere close to capacity.</p>
<h2>The Pacific Northwest</h2>
<p>The Pacific Northwest isn’t having as much rain and snow, and it’s a little drier there. But it’s <a href="https://www.wcc.nrcs.usda.gov/ftpref/data/water/wcs/gis/maps/wa_swepctnormal_update.pdf">close to average</a>, so there’s not a huge concern there, at least not right now.</p>
<p><iframe id="de2oY" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/de2oY/3/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>Forests, range land and the fire risk</h2>
<p>Drought can also have longer-term impacts on ecosystems, particularly forest health.</p>
<p>The Sierra Nevada range has seen <a href="https://doi.org/10.1038/s41561-019-0388-5">large-scale tree die-offs</a> with the drought in recent years, <a href="https://www.fs.usda.gov/Internet/FSE_DOCUMENTS/fseprd1088611.pdf">including in northern areas</a> around Lake Tahoe and Reno that weren’t as affected by the previous drought. Whether the recent die-offs there are due to the severity of the current drought or lingering effects from the past droughts is an open question. </p>
<p>Even with a wet winter, it’s not clear how soon the forests will recover.</p>
<p>Rangelands, since they are mostly grasses, can recover in a few months. The <a href="https://gbdash.dri.edu/forecasts.php">soil moisture is really high</a> in a lot of these areas, so range conditions should be good across the West – at least going into summer. </p>
<figure class="align-center ">
<img alt="Dead and dying trees with yellow needles on a forest ridge." src="https://images.theconversation.com/files/514984/original/file-20230313-23-va5wq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/514984/original/file-20230313-23-va5wq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/514984/original/file-20230313-23-va5wq9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/514984/original/file-20230313-23-va5wq9.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/514984/original/file-20230313-23-va5wq9.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/514984/original/file-20230313-23-va5wq9.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/514984/original/file-20230313-23-va5wq9.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">Drought and bark beetles have killed millions of trees across California in recent years, contributing to wildfire risk.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/dead-and-dying-trees-are-seen-in-a-forest-stressed-by-news-photo/472531110">David McNew/Getty Images</a></span>
</figcaption>
</figure>
<p>If the West has another really hot, dry summer, however, the drought could ramp up again, particularly in the Northwest and California. And then communities will have to <a href="https://ui.adsabs.harvard.edu/abs/2021AGUFM.H53G..06H/abstract">think about fire risk</a>.</p>
<p>Right now, there’s a <a href="https://www.predictiveservices.nifc.gov/outlooks/outlooks.htm">below-normal likelihood of big fires</a> in the Southwest for early spring due to lots of soil moisture and snowpack.</p>
<p>In the higher-elevation mountains and forests, the above-average snowpack is likely to last longer than it has in recent years, so those regions will likely have a later start to the fire season. But lower elevations, like the Great Basin’s shrub- and grassland-dominated ecosystem, could see fire danger starting earlier in the year if the land dries out.</p>
<h2>Long-term outlooks aren’t necessarily reliable</h2>
<p>By a lot of atmospheric measures, California appears to be coming <a href="https://droughtmonitor.unl.edu/data/png/20230314/20230314_usdm.png">out of drought</a>, and the drought feels like it’s ending elsewhere. But it’s hard to say when exactly the drought is over. Studies suggest the <a href="https://doi.org/10.1002/joc.7513">West’s hydroclimate is becoming more variable</a> in its swings from drought to deluge.</p>
<p>Drought is also hard to forecast, particularly <a href="https://www.cpc.ncep.noaa.gov/products/expert_assessment/sdo_discussion.php">long term</a>. Researchers can get a pretty good sense of conditions one month out, but the chaotic nature of the atmosphere and weather make longer-range outlooks less reliable.</p>
<p>We saw that this year. The <a href="https://www.noaa.gov/news-release/us-winter-outlook-warmer-drier-south-with-ongoing-la-nina">initial forecast</a> was for a dry winter 2023 in much of the West. But in California, Arizona and New Mexico, the opposite happened.</p>
<p>Seasonal forecasts tend to rely heavily on whether it’s <a href="https://oceanservice.noaa.gov/facts/ninonina.html">an El Niño or La Niña year</a>, involving sea surface temperatures in the tropical Pacific that can affect the jet stream and atmospheric conditions around the world. During La Niña – the pattern we saw from 2020 until <a href="https://www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory/ensodisc.shtml">March 2023</a> – the Southwest tends to be drier and the Pacific Northwest wetter.</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 El Niño and La Niña.</span></figcaption>
</figure>
<p>But that pattern <a href="https://www.climate.gov/news-features/blogs/did-la-ni%C3%B1a-drench-southwest-united-states-early-winter-202223">doesn’t always set up</a> in exactly the same way and in the same place, as we saw this year. </p>
<p>There is <a href="https://doi.org/10.1002/joc.7513">a lot more going on in the atmosphere</a> and the oceans on a short-term scale that can dominate the La Niña pattern. This year’s <a href="https://www.nesdis.noaa.gov/news/atmospheric-rivers-hit-west-coast">series of atmospheric rivers</a> has been one example. </p>
<p><em>Editor’s note: This article was updated on March 22, 2023, with the latest snowpack map.</em></p><img src="https://counter.theconversation.com/content/201156/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Dan McEvoy 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>Reservoirs and streams are in good shape in California and the Great Basin, but groundwater and ecosystems are another story. And then there’s the Colorado River Basin.Dan McEvoy, Associate Research Professor in Climatology, Desert Research InstituteLicensed 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>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1635329743099949059"}"></div></p>
<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/1731422021-12-07T13:33:52Z2021-12-07T13:33:52ZCalifornia’s water supplies are in trouble as climate change worsens natural dry spells, especially in the Sierra Nevada<figure><img src="https://images.theconversation.com/files/435786/original/file-20211206-21-d69ztq.jpg?ixlib=rb-1.1.0&rect=835%2C323%2C3673%2C2254&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Several of California's reservoirs were at less than one-third of their capacity in early December 2021.</span> <span class="attribution"><span class="source">Martha Conklin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>California is preparing for a third straight year of drought, and officials are tightening limits on water use to levels never seen so early in the water year. Most of the state’s water reservoirs are <a href="https://cdec.water.ca.gov/resapp/RescondMain">well below average</a>, with several at less than a third of their capacity. The <a href="https://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=2">outlook for rain and snow this winter</a>, when most of the state’s yearly precipitation arrives, isn’t promising.</p>
<p>Especially worrying is the outlook for the Sierra Nevada, the long mountain chain that runs through the eastern part of the state. California’s cities and its farms – which grow <a href="https://www.cdfa.ca.gov/Statistics/">over a third of the nation’s vegetables</a> and two-thirds of its fruit and nuts – rely on runoff from the mountains’ snowpack for water.</p>
<p>As <a href="https://scholar.google.com/citations?user=S2cxf2IAAAAJ&hl=en">an engineer</a>, I have studied California’s water and climate for over 30 years. A closer look at California’s water resources shows the challenge ahead and how climate change is putting the state’s water supply and agriculture at greater risk.</p>
<h2>Where California gets its water</h2>
<p>Statewide, California averages about 2 feet of precipitation per year, about two-thirds of the global average, giving the state as a whole a semi-arid climate.</p>
<p>The majority of California’s rain and snow falls in the mountains, primarily in winter and spring. But agriculture and coastal cities need that water to get through the dry summers. To get water to dry Southern California and help with flood control in the north, California over the past century developed <a href="https://water.ca.gov/Programs/State-Water-Project/SWP-Facilities/History">a statewide system</a> of reservoirs, tunnels and canals that brings water from the mountains. The largest of those projects, the State Water Project, delivers water from the higher-precipitation northern Sierra to the southern half of the state.</p>
<figure class="align-center ">
<img alt="A large, manmade canal flows through low hills." src="https://images.theconversation.com/files/436038/original/file-20211207-17-k5lghw.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436038/original/file-20211207-17-k5lghw.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436038/original/file-20211207-17-k5lghw.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436038/original/file-20211207-17-k5lghw.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436038/original/file-20211207-17-k5lghw.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436038/original/file-20211207-17-k5lghw.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436038/original/file-20211207-17-k5lghw.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 section of the California Aqueduct within the State Water Project.</span>
<span class="attribution"><span class="source">Ken James/California Department of Water Resources</span></span>
</figcaption>
</figure>
<p>To track where the water goes, it’s useful to look at the volume in acre-feet. California is about 100 million acres in area, so at 2 feet per year, its annual precipitation averages about 200 million acre-feet.</p>
<p>Of that 200, an average of only about 80 million acre-feet heads downstream. Much of the water returns to the atmosphere through <a href="https://www.usgs.gov/special-topic/water-science-school/science/evapotranspiration-and-water-cycle?qt-science_center_objects">evapotranspiration</a> by plants and trees in the Sierra Nevada or North Coast forests. Of the 80 million acre-feet that does run off, about half remains in the aquatic environment, such as rivers flowing to the ocean. That leaves about 41 million acre-feet for downstream use. About 80% of that goes for agriculture and 20% for urban uses.</p>
<p>In wet years, there may be much more than 80 million acre-feet of water available, but in dry years, it can be much less.</p>
<p>In 2020, for example, California’s precipitation was <a href="https://water.ca.gov/Current-Conditions">less than two-thirds of average</a>, and the State Water Project delivered only 5% of the contracted amounts. The state’s other main aqueduct systems that move water around the state also severely reduced their supplies.</p>
<p>The 2021 water year, which ended Sept. 30, was one of the three driest on record for the Sierra Nevada. Precipitation was about <a href="https://water.ca.gov/Current-Conditions">44% of average</a>. With limited precipitation as of December 2021 and the state in <a href="https://twitter.com/NWSBayArea/status/1466766767573798914">extreme drought</a>, the State Water Project cut its preliminary allocations for water agencies to 0% for 2022, with small amounts still flowing for health and safety needs. </p>
<p>While conditions could improve if more storms come in the next three months, the official National Oceanic and Atmospheric Administration outlook points to <a href="https://www.cpc.ncep.noaa.gov/products/predictions/long_range/seasonal.php?lead=2">below-normal precipitation being more likely than above normal</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/436055/original/file-20211207-136955-odxbx4.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Comparison of state maps with water uses in wet and dry years" src="https://images.theconversation.com/files/436055/original/file-20211207-136955-odxbx4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436055/original/file-20211207-136955-odxbx4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=683&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436055/original/file-20211207-136955-odxbx4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=683&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436055/original/file-20211207-136955-odxbx4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=683&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436055/original/file-20211207-136955-odxbx4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=858&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436055/original/file-20211207-136955-odxbx4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=858&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436055/original/file-20211207-136955-odxbx4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=858&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"><a class="source" href="https://water.ca.gov/-/media/DWR-Website/Web-Pages/Programs/California-Water-Plan/Docs/Update2018/Final/California-Water-Plan-Update-2018.pdf">California State Water Plan 2018</a></span>
</figcaption>
</figure>
<h2>Drought and a warming climate</h2>
<p>Multiyear dry periods, when annual precipitation is below average, are a feature of California’s climate, but rising global temperatures are also having an impact.</p>
<p>Over the past 1,100 years, there has been at least one dry period lasting four years or longer each century. There have been two in the past 35 years – 1987-92 and 2012-15. A warmer climate intensifies the effect of these dry periods, as drier soil and drier air stress both natural vegetation and crops.</p>
<p>Rising global temperatures affect runoff from the Sierra Nevada, which provides <a href="https://sierranevada.ca.gov/what-we-do/water-supply/">over 60% of California’s developed water supply</a>.</p>
<p>Over 80% of the runoff in the central and southern Sierra Nevada comes from the snow zone. In the wetter but lower-elevation northern Sierra, rainfall contributes over <a href="https://doi.org/10.3389/frwa.2021.655485">one-third of the annual runoff</a>.</p>
<p>The average snowline, the elevation above which most precipitation is snow, goes from about 5,000 feet elevation in the north to 7,000 feet in the south. On average, <a href="https://doi.org/10.1111/1752-1688.12647">each 1.8 degrees Fahrenheit (1 Celsius) of warming</a> could push the snowline another 500 feet higher, reducing the snow total. </p>
<p>Shifts from snow to rain and earlier runoff also mean that more of the capacity behind existing dams will be allocated to flood control, further reducing their capacity for seasonal water-supply storage.</p>
<figure class="align-center ">
<img alt="A dry ring around the reservoir shows how low its water level is." src="https://images.theconversation.com/files/436045/original/file-20211207-17-o1e5g4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/436045/original/file-20211207-17-o1e5g4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=389&fit=crop&dpr=1 600w, https://images.theconversation.com/files/436045/original/file-20211207-17-o1e5g4.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=389&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/436045/original/file-20211207-17-o1e5g4.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=389&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/436045/original/file-20211207-17-o1e5g4.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=489&fit=crop&dpr=1 754w, https://images.theconversation.com/files/436045/original/file-20211207-17-o1e5g4.jpeg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=489&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/436045/original/file-20211207-17-o1e5g4.jpeg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=489&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">A section of Shasta Lake, California’s largest reservoir, on Oct. 28, 2021.</span>
<span class="attribution"><span class="source">Andrew Innerarity/California Department of Water Resources</span></span>
</figcaption>
</figure>
<p><a href="https://doi.org/10.1029/2019GL083770">A wealth of research</a> has established that the Sierra Nevada could see <a href="https://www.nature.com/articles/s43017-021-00219-y.epdf">low- to no-snow winters for years at a time</a> by the late 2040s if greenhouse gases emissions don’t decline, with <a href="https://theconversation.com/climate-change-will-mean-more-multiyear-snow-droughts-in-the-west-121406">conditions worsening</a> beyond that possible. </p>
<p>Warming will also <a href="https://doi.org/10.1073/pnas.1319316111">increase water demand from forests as growing seasons lengthen</a> and drive both <a href="https://doi.org/10.1038/s41561-019-0388-5">drought stress leading to tree mortality</a> and increased <a href="https://theconversation.com/climate-change-and-wildfires-how-do-we-know-if-there-is-a-link-101304">risk of high-severity wildfires</a>. </p>
<h2>Sustainability in a warming climate</h2>
<p>Water storage is central to California’s water security.</p>
<p>Communities and farms can <a href="https://theconversation.com/ancient-groundwater-why-the-water-youre-drinking-may-be-thousands-of-years-old-167982">pump more groundwater</a> when supplies are low, but the state has been pumping out more water than it replenished in wet years. Parts of the state rely on water from the Colorado River, whose dams provide for several years of water storage, but the basin <a href="https://theconversation.com/climate-change-is-shrinking-the-colorado-river-76280">lacks the runoff</a> <a href="https://www.usbr.gov/newsroom/#/news-release/3950">to fill the dams</a>.</p>
<p>Public opposition has made it difficult to build new dams, so better use of groundwater for both seasonal and multiyear storage is crucial.</p>
<figure class="align-center ">
<img alt="Aerial view of a recharge ponds" src="https://images.theconversation.com/files/435973/original/file-20211206-21-1rkabet.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/435973/original/file-20211206-21-1rkabet.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=558&fit=crop&dpr=1 600w, https://images.theconversation.com/files/435973/original/file-20211206-21-1rkabet.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=558&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/435973/original/file-20211206-21-1rkabet.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=558&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/435973/original/file-20211206-21-1rkabet.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=701&fit=crop&dpr=1 754w, https://images.theconversation.com/files/435973/original/file-20211206-21-1rkabet.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=701&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/435973/original/file-20211206-21-1rkabet.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=701&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Groundwater banking, or recharging groundwater during wet periods, is crucial to weathering multiyear droughts. Shallow ponds like these allow water to sink into underground aquifers.</span>
<span class="attribution"><span class="source">Dale Kolke/California Department of Water Resources</span></span>
</figcaption>
</figure>
<p>The state’s <a href="https://water.ca.gov/Programs/Groundwater-Management/SGMA-Groundwater-Management">Sustainable Groundwater Management Act</a> requires local agencies to develop sustainability plans. That provides some hope that groundwater pumping and replenishment can be brought into balance, most likely by leaving some cropland unplanted. Managed aquifer recharge south of the Sacramento-San Joaquin Delta is gradually expanding, and much more can be done.</p>
<p>[<em>Get the best of The Conversation, every weekend.</em> <a href="https://memberservices.theconversation.com/newsletters/?source=inline-weeklybest">Sign up for our weekly newsletter</a>.]</p>
<p>If the state doesn’t do more, including tactics such as applying desalination technology to make saltwater usable, urban areas can expect the 25% cuts in water use put in place during the 2012-15 drought to be more common and potentially even deeper.</p>
<p>California’s water resources can provide for a healthy environment, robust economy and sustainable agricultural use. Achieving this will require upgrading both natural infrastructure – headwaters forests, floodplains and groundwater recharge in agricultural areas – and built infrastructure, such as canals, spillways and levees. The <a href="https://resources.ca.gov/Initiatives/Building-Water-Resilience/portfolio">information is available</a>; officials now have to follow through.</p><img src="https://counter.theconversation.com/content/173142/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Roger Bales receives research support from and consults for Blue Forest and for The Nature Conservancy. Both are non-profit conservation organizations implementing forest-restoration projects in California, He also receives research support from state and federal agencies. </span></em></p>The State Water Project cut its initial allocations for water agencies to 0% for 2022. A California water expert explains why.Roger Bales, Distinguished Professor of Engineering, University of California, MercedLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1703352021-10-21T18:05:28Z2021-10-21T18:05:28ZEvacuations ordered as a powerful storm heads for California’s wildfire burn scars, raising risk of mudslides – this is what cascading climate disasters look like<figure><img src="https://images.theconversation.com/files/427872/original/file-20211021-16-1pz7dho.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C4366%2C2848&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A firefighter checks homes after a mudslide that killed 23 people in Montecito, Calif., in 2018.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/cal-firefighter-alex-jimenez-walks-out-after-marking-a-spot-news-photo/903512378">Wally Skalij/Los Angeles Times via Getty Images</a></span></figcaption></figure><p>Officials <a href="https://twitter.com/EliasonMike/status/1452302654604992518">issued</a> <a href="https://twitter.com/CALFIRECZU/status/1452306261232455686">evacuation</a> <a href="https://twitter.com/sf_edie/status/1452291775306076171">orders</a> for people living downhill from several of California’s wildfire burn scars on Oct. 24, 2021, as a powerful storm system known as an <a href="https://theconversation.com/atmospheric-river-storms-can-drive-costly-flooding-and-climate-change-is-making-them-stronger-128902">atmospheric river</a> began to drench the West Coast. </p>
<p>While the storm brings much-needed water to a region in the midst of an historic drought, and should significantly lower the wildfire risk after a destructive fire year, it also brings dangerous new flood and mudslide risks, particularly in areas <a href="https://theconversation.com/moving-beyond-americas-war-on-wildfire-4-ways-to-avoid-future-megafires-168898">recovering from wildfires</a>.</p>
<p>Wildfires strip away vegetation and leave the soil less able to absorb water. A downpour on these vulnerable landscapes can quickly erode the ground as fast-moving water carries debris and mud with it. </p>
<p>The National Weather Service issued flash flood warnings and <a href="https://twitter.com/NWSSacramento/status/1451207133593149441">warned of ash and debris flows</a> through Oct. 26 in several areas that recently burned, including the sites of the <a href="https://twitter.com/NWSLosAngeles/status/1452303544376246272">Alisal Fire</a> near Santa Barbara, California, and the nearly 1-million-acre <a href="https://twitter.com/NWSSacramento/status/1452250009555148800">Dixie Fire</a> in the Sierra Nevada. Near San Jose, two counties ordered evacuations near large areas that burned in the <a href="https://twitter.com/sf_edie/status/1452291775306076171">Santa Cruz Mountains</a> in 2020.</p>
<p>I study cascading hazards like this, in which <a href="https://doi.org/10.1038/d41586-018-06783-6">consecutive events lead to human disasters</a>. Studies show climate change is raising the risk of multiple compound disasters, and it’s clear that communities and government agencies aren’t prepared.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1450117299940122632"}"></div></p>
<h2>When storms hit burn scars</h2>
<p>California has experienced this kind of cascading disaster before.</p>
<p>In early 2017, following years of drought, the region had a wet winter that fueled dense growth of vegetation and shrubs. An unusually warm and dry spring and summer followed, and it dried out the vegetation, turning it into fuel ready to burn. That fall, extreme Santa Ana and Diablo winds – known for their sustained low humidity – created the <a href="https://doi.org/10.1146/annurev-earth-071719-055228">perfect conditions for wildfires</a>.</p>
<p>The <a href="https://www.fire.ca.gov/incidents/2017/12/4/thomas-fire/">Thomas Fire</a> began near Santa Barbara in December 2017 and burned over 280,000 acres. The following January, extreme rainfall hit the region, including the burn scar left by the fire, and caused the deadliest <a href="https://doi.org/10.1146/annurev-earth-071719-055228">mudslide-debris flow event</a> in California’s history. More than 400 homes were destroyed in about <a href="https://youtu.be/2cgkcFsLEho">two hours</a>, and 23 people died.</p>
<figure class="align-center ">
<img alt="Illustrations of four stages in a cascading disaster, from drought to spring growth to fires to mudslides." src="https://images.theconversation.com/files/427609/original/file-20211020-16-13latw6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/427609/original/file-20211020-16-13latw6.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=434&fit=crop&dpr=1 600w, https://images.theconversation.com/files/427609/original/file-20211020-16-13latw6.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=434&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/427609/original/file-20211020-16-13latw6.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=434&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/427609/original/file-20211020-16-13latw6.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=546&fit=crop&dpr=1 754w, https://images.theconversation.com/files/427609/original/file-20211020-16-13latw6.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=546&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/427609/original/file-20211020-16-13latw6.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=546&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 the cascading effects of climate change for wildfires.</span>
<span class="attribution"><a class="source" href="https://doi.org/10.1146/annurev-earth-071719-055228">AghaKouchak et al., Annual Review of Earth and Planetary Sciences, 2020</a></span>
</figcaption>
</figure>
<p>These kinds of cascading events aren’t unique to California. Australia’s Millennium Drought (1997-2009) also ended with <a href="https://doi.org/10.1002/wrcr.20123">devastating floods</a> that inundated urban areas and breached <a href="https://doi.org/10.1061/(ASCE)GT.1943-5606.0001465">levees</a>. A study linked some of the levee and dike failures to earlier drought conditions, such as cracks forming because of exposure to heat and dryness.</p>
<h2>Individually, they might not have been disasters</h2>
<p>When multiple hazards, such as droughts, heat waves, wildfires and extreme rainfall, interact, human disasters often result.</p>
<p>The individual drivers might not be very extreme on their own, but combined they can become lethal. These types of events are broadly referred to as compound events – for example, a drought and heat wave hitting at the same time. Their combined impact can be harder to forecast. A cascading event involves compound <a href="https://doi.org/10.1038/s43017-020-0060-z">events in succession</a>, like wildfires followed by downpours and mudslides.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/2cgkcFsLEho?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">Video shows how quickly a mudslide overtakes a town.</span></figcaption>
</figure>
<p>While the drivers and physical mechanisms behind compound and cascading events are not fully understood, they are often linked to large-scale circulation patterns like the El Niño-Southern Oscillation (ENSO). Meanwhile, lack of preparedness and high degrees of vulnerability at the local level can also increase the impacts of multiple connected events.</p>
<p>With compound and cascading events likely to become more common in a warming world, being able to prepare for and manage multiple hazards will be increasingly essential. </p>
<h2>Climate change intensifies the risk</h2>
<p><a href="https://doi.org/10.1002/2014GL062308">Several</a> <a href="https://doi.org/10.1073/pnas.1503667112">research studies</a> have shown that compound events with both drought and heat waves have <a href="https://doi.org/10.1002/2015GL064924">become more severe and frequent</a> in recent years. <a href="https://doi.org/10.1073/pnas.1422385112">One study</a> attributed the increase in the risk of these dry-warm events in California to human-caused global warming and projected that the increased risk of dry-warm conditions will continue in the future.</p>
<p>An important physical process responsible for increases in compound drought and heat is land-atmosphere interactions. Evaporation from soil cools down the land surface, similar to how the human body cools down by sweating. During droughts, the <a href="https://doi.org/10.1175/JCLI4288.1">lack of moisture limits soil evaporation</a>, which increases the surface temperature and eventually the air temperature in the area. Data shows temperatures during droughts are <a href="https://doi.org/10.1126/sciadv.aat2380">rising in many parts</a> of the United States, including the Southwest – a pattern that is expected to <a href="https://doi.org/10.1029/2019EF001461">continue in the future</a>.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/427697/original/file-20211021-13-109lx1y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/427697/original/file-20211021-13-109lx1y.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=432&fit=crop&dpr=1 600w, https://images.theconversation.com/files/427697/original/file-20211021-13-109lx1y.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=432&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/427697/original/file-20211021-13-109lx1y.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=432&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/427697/original/file-20211021-13-109lx1y.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=543&fit=crop&dpr=1 754w, https://images.theconversation.com/files/427697/original/file-20211021-13-109lx1y.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=543&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/427697/original/file-20211021-13-109lx1y.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=543&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Most of the West is still in severe drought.</span>
<span class="attribution"><a class="source" href="https://www.drought.gov/current-conditions">NOAA/NDIS</a></span>
</figcaption>
</figure>
<p>Numerous studies have also shown that <a href="https://doi.org/10.1007/s00477-020-01885-y">droughts and heat waves increase</a> the <a href="https://doi.org/10.1073/pnas.1607171113">likelihood of wildfires</a>. And wildfires can trigger other cascading hazards, turning otherwise unexceptional events into <a href="https://doi.org/10.1038/d41586-018-06783-6">human disasters</a>.</p>
<p>At the same time, extreme rainfall events are <a href="https://doi.org/10.1038/s41558-018-0140-y">expected to intensify</a> <a href="https://doi.org/10.1002/2017WR021975">in a warming climate</a>. A warmer atmosphere can hold more moisture, leading to wetter storms. This means there will likely be more burned acres exposed to potentially extreme rainfall events in a warmer world.</p>
<p>[<em>You’re smart and curious about the world.</em> <a href="https://theconversation.com/us/newsletters/the-daily-3?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=youresmart">You can read The Conversation daily by subscribing to our newsletter</a>.]</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/427847/original/file-20211021-23-15jtecx.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map showing 2021 wildfire burn areas" src="https://images.theconversation.com/files/427847/original/file-20211021-23-15jtecx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/427847/original/file-20211021-23-15jtecx.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=384&fit=crop&dpr=1 600w, https://images.theconversation.com/files/427847/original/file-20211021-23-15jtecx.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=384&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/427847/original/file-20211021-23-15jtecx.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=384&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/427847/original/file-20211021-23-15jtecx.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/427847/original/file-20211021-23-15jtecx.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/427847/original/file-20211021-23-15jtecx.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=482&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Large parts of northern California and southern Oregon had fires in 2021, some still burning in mid-October.</span>
<span class="attribution"><a class="source" href="https://maps.nwcg.gov/sa/#/%3F/%3F/41.062/-121.1352/8">National Wildfire Coordinating Group</a></span>
</figcaption>
</figure>
<p>Cascading hazards are not limited to <a href="https://doi.org/10.1088/1748-9326/ab41a6">rain over burned areas</a>. Soot and ash <a href="https://doi.org/10.1029/2006JD008003">deposits on snowpack</a> can increase snowmelt, change the timing of runoff and cause snow-driven flooding. Fires are not only increasing in size and severity, they are also occurring at higher <a href="https://doi.org/10.1073/pnas.2009717118">elevations and well above the snow line</a>.</p>
<p>It’s also important to recognize that human activities and local infrastructure can also affect extreme events. Urbanization and deforestation, for example, can intensify flooding and worsen mud or debris flow events and their impacts.</p>
<h2>Managing multiple disasters and climate change</h2>
<p>Despite the high risk when extreme rainfall and droughts interact, most research in this area focuses on only one or the other. Different government agencies oversee flood and drought monitoring, warning and management, even though both are extremes of the same <a href="https://theconversation.com/the-water-cycle-is-intensifying-as-the-climate-warms-ipcc-report-warns-that-means-more-intense-storms-and-flooding-165590">hydrological cycle</a>.</p>
<figure class="align-center ">
<img alt="Burned trees on a hillside with no needles and a fire-damaged home. The ground is bare." src="https://images.theconversation.com/files/427843/original/file-20211021-16-1vglxg5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/427843/original/file-20211021-16-1vglxg5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/427843/original/file-20211021-16-1vglxg5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/427843/original/file-20211021-16-1vglxg5.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/427843/original/file-20211021-16-1vglxg5.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/427843/original/file-20211021-16-1vglxg5.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/427843/original/file-20211021-16-1vglxg5.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 aerial view of the location of the Dixie Fire near Greenville shows the bare soil left behind.</span>
<span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/in-an-aerial-view-the-remains-of-a-home-that-was-destroyed-news-photo/1342340548">Justin Sullivan/Getty Images</a></span>
</figcaption>
</figure>
<p>Recent studies and disasters show a strong need to <a href="https://doi.org/10.1016/j.wasec.2020.100070">integrate management and risk reduction</a> strategies of droughts and flood. Focusing on one hazard by one agency can potentially have <a href="https://doi.org/10.1038/s41893-018-0159-0">unintended consequences</a> for another hazard. For example, <a href="https://doi.org/10.1016/j.wasec.2020.100070">maximizing reservoir storage</a> when expecting a drought can increase the flood risk.</p>
<p>As a society, we cannot prevent cascading hazards from happening. But we can become better prepared for plausible cascading hazards in a changing climate.</p>
<hr>
<p>
<em>
<strong>
Read more:
<a href="https://theconversation.com/atmospheric-river-storms-can-drive-costly-flooding-and-climate-change-is-making-them-stronger-128902">Atmospheric river storms can drive costly flooding – and climate change is making them stronger</a>
</strong>
</em>
</p>
<hr>
<p><em>This article was updated Oct. 24, 2021, with evacuation orders issued near several wildfire burn scars.</em></p><img src="https://counter.theconversation.com/content/170335/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Amir AghaKouchak receives funding from NSF, NASA, NOAA, and Caltrans.</span></em></p>Studies show climate change is raising the risk of cascading hazards that alone might not be extreme but add up to human disasters. Communities and government agencies aren’t prepared.Amir AghaKouchak, Professor of Civil & Environmental Engineering and Earth System Science, University of California, IrvineLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1677062021-09-13T12:14:50Z2021-09-13T12:14:50ZWestern fires are burning higher in the mountains and at unprecedented rates as the climate warms<figure><img src="https://images.theconversation.com/files/420425/original/file-20210910-21-1pbdpxm.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C3000%2C1994&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Heat and dryness are leaving high mountain areas more vulnerable to forest fires.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/news-photo/the-241-square-mile-station-fire-continues-to-blacken-news-photo/90351732"> David McNew/Getty Images</a></span></figcaption></figure><p>The Western U.S. is experiencing <a href="https://disasterphilanthropy.org/disaster/2021-north-american-wildfire-season/">another severe fire season</a>, and a recent study shows that even high mountain areas once considered too wet to burn are at increasing risk as the climate warms.</p>
<p>With <a href="https://www.nifc.gov/fire-information/nfn">more than 5 million acres already burned by early September</a>, the 2021 U.S. fire season is <a href="https://www.nifc.gov/fire-information/nfn">about on pace</a> with the extreme fire season of 2020. This summer has been <a href="https://www.ncei.noaa.gov/news/national-climate-202108">the hottest</a> on record and one of the driest in the region, with <a href="https://droughtmonitor.unl.edu/data/jpg/20210907/20210907_usdm.jpg">80% of the Western U.S.</a> in severe to exceptional drought. That combination of heat and dryness is a recipe for <a>disastrous wildfires</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/420624/original/file-20210912-46896-ipnb6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Map of the contiguous United States with historic temperature ranks on each state. Several were the hottest on record or close to it." src="https://images.theconversation.com/files/420624/original/file-20210912-46896-ipnb6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/420624/original/file-20210912-46896-ipnb6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=431&fit=crop&dpr=1 600w, https://images.theconversation.com/files/420624/original/file-20210912-46896-ipnb6j.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=431&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/420624/original/file-20210912-46896-ipnb6j.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=431&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/420624/original/file-20210912-46896-ipnb6j.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=542&fit=crop&dpr=1 754w, https://images.theconversation.com/files/420624/original/file-20210912-46896-ipnb6j.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=542&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/420624/original/file-20210912-46896-ipnb6j.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=542&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Several states saw their hottest June-August period since consistent record keeping began in the 1890s.</span>
<span class="attribution"><a class="source" href="https://www.ncei.noaa.gov/news/national-climate-202108">NOAA</a></span>
</figcaption>
</figure>
<p>In a study in the Proceedings of the National Academy of Sciences released in May 2021, <a href="https://scholar.google.com/citations?user=S1J4kAoAAAAJ&hl=en">our team of fire</a> and <a href="https://scholar.google.com/citations?user=tGGNDyUAAAAJ&hl=en">climate scientists</a> <a href="https://scholar.google.ca/citations?user=ZaW8ZbsAAAAJ&hl=en">and engineers</a> found that forest fires are now <a href="https://www.pnas.org/content/118/22/e2009717118">reaching higher, normally wetter elevations</a>. And they are burning there at rates unprecedented in recent fire history. Two fires burning in northern California in 2021 – the Dixie and Caldor fires – are examples: They were the first and second wildfires on record to cross the Sierra Nevada crest and burn on both sides.</p>
<p>While <a href="https://theconversation.com/how-years-of-fighting-every-wildfire-helped-fuel-the-western-megafires-of-today-163165">historical fire suppression</a> and other forest management practices play a role in the West’s worsening fire problem, the high-elevation forests we studied have had little human intervention. The results provide a clear indication that climate change is enabling these normally wet forests to burn. </p>
<p>As wildfires creep higher up mountains, another tenth of the West’s forest area is now at risk, our study found. That creates new hazards for mountain communities, with impacts on downstream water supplies and the plants and wildlife that call these forests home.</p>
<figure class="align-center ">
<img alt="Map showing how high-elevation forest fires advanced uphill." src="https://images.theconversation.com/files/402231/original/file-20210523-21-1xdrd55.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402231/original/file-20210523-21-1xdrd55.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=627&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402231/original/file-20210523-21-1xdrd55.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=627&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402231/original/file-20210523-21-1xdrd55.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=627&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402231/original/file-20210523-21-1xdrd55.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=787&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402231/original/file-20210523-21-1xdrd55.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=787&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402231/original/file-20210523-21-1xdrd55.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=787&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Forest fires advanced to higher elevations as the climate dried from 1984 to 2017. Every 200 meters equals 656 feet.</span>
<span class="attribution"><span class="source">Mojtaba Sadegh</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Rising fire risk in the high mountains</h2>
<p>In the <a href="https://www.pnas.org/content/118/22/e2009717118">new study</a>, we analyzed records of all fires larger than 1,000 acres (405 hectares) in the mountainous regions of the contiguous Western U.S. between 1984 and 2017.</p>
<p>The amount of land that burned increased across all elevations during that period, but the largest increase occurred above 8,200 feet (2,500 meters). To put that elevation into perspective, Denver – the mile-high city – sits at 5,280 feet, and Aspen, Colorado, is at 8,000 feet. These high-elevation areas are largely remote mountains and forests with some small communities and ski areas.</p>
<p>The area burning above 8,200 feet more than tripled in 2001-2017 compared with 1984-2000. </p>
<figure class="align-center ">
<img alt="Fire lights up a ridge behind a farm." src="https://images.theconversation.com/files/402236/original/file-20210523-15-1hxi37i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402236/original/file-20210523-15-1hxi37i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=343&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402236/original/file-20210523-15-1hxi37i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=343&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402236/original/file-20210523-15-1hxi37i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=343&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402236/original/file-20210523-15-1hxi37i.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=431&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402236/original/file-20210523-15-1hxi37i.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=431&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402236/original/file-20210523-15-1hxi37i.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=431&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">One of Colorado’s largest wildfires, 2020’s East Troublesome Fire, crossed the Continental Divide and was burning at elevations around 9,000 feet in October, when snow normally would have been falling.</span>
<span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/Exchange-ColoradoWildfires-Blow-ups/8e10c8213c3847f3a7ef14e7ff81eddf/photo">AP Photo/David Zalubowski</a></span>
</figcaption>
</figure>
<p>Our results show that climate warming has diminished the high-elevation flammability barrier – the point where forests historically were too wet to burn regularly because the snow normally lingered well into summer and started falling again early in the fall. Fires advanced about 826 feet (252 meters) uphill in the Western mountains over those three decades.</p>
<p>The <a href="https://inciweb.nwcg.gov/incident/6964/">Cameron Peak Fire in Colorado</a> in 2020 was the largest fire in the state’s history, burning over 208,000 acres (84,175 hectares), and is a prime example of a high-elevation forest fire. The fire burned in forests extending to 12,000 feet (3,658 meters) and reached the upper tree line of the Rocky Mountains. </p>
<p>We found that rising temperatures in the past 34 years have helped to extend the fire territory in the West to an additional 31,470 square miles (81,507 square kilometers) of high-elevation forests. That means a staggering 11% of all Western U.S. forests – an area similar in size to South Carolina – are susceptible to fire now that weren’t three decades ago. </p>
<h2>Can’t blame fire suppression here</h2>
<p>In lower-elevation forests, several factors contribute to fire activity, including the presence of more people in wildland areas and a history of fire suppression. </p>
<p>In the early 1900s, Congress commissioned the U.S. Forest Service to <a href="https://foresthistory.org/research-explore/us-forest-service-history/policy-and-law/fire-u-s-forest-service/u-s-forest-service-fire-suppression/">manage forest fires</a>, which resulted in a focus on suppressing fires – a policy that continued through the 1970s. This caused flammable underbrush that would normally be cleared out by occasional natural blazes to accumulate. The increase in biomass in many lower elevation forests across the West has been associated with increases in <a href="https://doi.org/10.1890/ES13-00217.1">high-severity fires and megafires</a>. At the same time, <a href="https://doi.org/10.1073/pnas.1607171113">climate warming has dried out forests in the Western U.S.</a>, making them more prone to large fires. </p>
<figure class="align-center ">
<img alt="Illustration of two mountains showing fires higher, less snow and more dead trees" src="https://images.theconversation.com/files/402233/original/file-20210523-19-46yvai.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/402233/original/file-20210523-19-46yvai.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=413&fit=crop&dpr=1 600w, https://images.theconversation.com/files/402233/original/file-20210523-19-46yvai.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=413&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/402233/original/file-20210523-19-46yvai.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=413&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/402233/original/file-20210523-19-46yvai.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=519&fit=crop&dpr=1 754w, https://images.theconversation.com/files/402233/original/file-20210523-19-46yvai.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=519&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/402233/original/file-20210523-19-46yvai.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=519&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">On average, fires have spread 826 feet (252 meters) higher into the mountains in recent decades, exposing an additional 31,470 square miles (81,507 square kilometers) of forests to fire.</span>
<span class="attribution"><span class="source">Mojtaba Sadegh</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>By focusing on high-elevation fires in areas with little history of fire suppression, we can more clearly see the influence of climate change. </p>
<p>Most high-elevation forests haven’t been subjected to much fire suppression, logging or other human activities, and because trees at these high elevations are in wetter forests, they historically have long <a href="https://www.fs.fed.us/database/feis/fire_regime_table/PNVG_fire_regime_table.html">return intervals between fires</a>, typically a century or more. Yet they experienced the highest rate of increase in fire activity in the past 34 years. We found that the increase is strongly correlated with the observed warming.</p>
<p><iframe id="87j2d" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/87j2d/1/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<h2>High mountain fires create new problems</h2>
<p>High-elevation fires have implications for natural and human systems. </p>
<p>High mountains are natural water towers that normally provide a sustained source of water to millions of people during dry summer months in the Western U.S. The scars that wildfires leave behind – known as burn scars – affect how much snow can accumulate at high elevations. This can influence the timing, <a href="https://doi.org/10.1021/es500130g">quality and</a> <a href="https://www.fs.fed.us/rm/pubs/rmrs_gtr042_4.pdf">quantity of water</a> that reaches reservoirs and rivers downstream.</p>
<p>High-elevation fires also remove standing trees that act as anchor points that normally stabilize the snowpack, <a href="https://doi.org/10.1016/j.foreco.2009.01.050">raising the risk of avalanches</a>.</p>
<p>The loss of tree canopy also exposes mountain streams to the Sun, <a href="https://doi.org/10.1890/09-0822.1">increasing water temperatures</a> in the cold headwater streams. Increasing stream temperatures can harm fish and the larger wildlife and predators that rely on them. </p>
<p>Climate change is increasing fire risk in many regions across the globe, and <a href="https://doi.org/10.1073/pnas.1003669107">studies show that this trend will continue</a> as the planet warms. The increase in fires in the high mountains is another warning to the U.S. West and elsewhere of the risks ahead as the climate changes.</p>
<p><em>This is an update to a story published <a href="https://theconversation.com/drafts/159699/edit">May 24, 2021</a>.</em></p>
<p>[<em>Understand new developments in science, health and technology, each week.</em> <a href="https://theconversation.com/us/newsletters/science-editors-picks-71/?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=science-understand">Subscribe to The Conversation’s science newsletter</a>.]</p><img src="https://counter.theconversation.com/content/167706/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Mojtaba Sadegh receives funding from the US National Science Foundation and the Joint Fire Science Program.</span></em></p><p class="fine-print"><em><span>John Abatzoglou receives funding from the National Science Foundation and the National Oceanic and Atmospheric Administration.</span></em></p><p class="fine-print"><em><span>Mohammad Reza Alizadeh 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>As the risk of fires rises in areas once considered too wet to burn, it creates hazards for mountain communities and for downstream water supplies.Mojtaba Sadegh, Assistant Professor of Civil Engineering, Boise State UniversityJohn Abatzoglou, Associate Professor of Engineering, University of California, MercedMohammad Reza Alizadeh, Ph.D. Student in Engineering, McGill UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1653522021-08-19T12:08:34Z2021-08-19T12:08:34ZWhen hotter and drier means more – but eventually less – wildfire<figure><img src="https://images.theconversation.com/files/415783/original/file-20210812-19-75kq61.jpg?ixlib=rb-1.1.0&rect=0%2C0%2C6038%2C4010&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Creek Fire burns near Shaver Lake, Calif., in the Sierra Nevada in September 2020.</span> <span class="attribution"><a class="source" href="https://newsroom.ap.org/detail/CaliforniaWildfires/fadd01e1646740c7ba63f68efdba0dc8/photo">AP Photo/Noah Berger</a></span></figcaption></figure><p>There is abundant evidence that changes in the climate, both <a href="https://www.pnas.org/content/113/42/11770">increased temperature</a> and <a href="https://www.pnas.org/content/115/36/E8349">reduced precipitation</a>, are making wildfires worse in the western U.S. The relationship between climate and wildfire seems obvious and universal: hotter + drier = more and worse wildfire.</p>
<p>Yet the diversity of wildland areas in the western U.S. means that <a href="https://doi.org/10.1002/eap.1420">not all ecosystems respond in the same way</a> to a hotter and drier climate. Understanding how and why climate change has different effects on wildfire is essential for effective management of our natural areas. </p>
<figure class="align-center ">
<img alt="A satellite-view map showing fire area with Yellowstone, the Sierra Nevada and the Sonoran Desert ecoregions marked" src="https://images.theconversation.com/files/414006/original/file-20210730-25-14i23th.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/414006/original/file-20210730-25-14i23th.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=812&fit=crop&dpr=1 600w, https://images.theconversation.com/files/414006/original/file-20210730-25-14i23th.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=812&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/414006/original/file-20210730-25-14i23th.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=812&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/414006/original/file-20210730-25-14i23th.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1020&fit=crop&dpr=1 754w, https://images.theconversation.com/files/414006/original/file-20210730-25-14i23th.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1020&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/414006/original/file-20210730-25-14i23th.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1020&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">All wildfires over about 12 acres in size from 1984-2019. Red indicates fires from 2010-2019.</span>
<span class="attribution"><a class="source" href="https://mtbs.gov/viewer/index.html">Jeremy Littell</a></span>
</figcaption>
</figure>
<h2>Why do areas respond differently?</h2>
<p>Similar to campfires, wildfires require fuel to burn: parts of trees and shrubs, the leaves, twigs and branches. Dried grasses, too, will work. The growth of this vegetation depends on water, and water availability depends on the climate.</p>
<p>How hot and dry the climate is in an area influences the amount of fuel that is available to burn and the strength of the relationship between wildfire and climate. <a href="http://scholar.google.com/citations?user=36K8XrUAAAAJ&hl=en">Ecologists</a> <a href="https://scholar.google.com/citations?user=VEf_brUAAAAJ&hl=en">such as</a> <a href="https://scholar.google.com/citations?hl=en&user=-lHGpDIAAAAJ">us</a> calculate how closely related wildfire area burned is to how hot and dry it is during the summer, and we have found that the relationship does indeed vary.</p>
<p>Areas that are historically cool and wet have a lot of fuel, but the fuel has to be dry enough to burn, so the relationship in these areas between wildfire and climate is very strong. Areas that are historically warm and dry have less fuel, often not enough fuel for a large wildfire even if it is very dry.</p>
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<p>Let’s consider one extreme. The Sonoran Desert in Arizona is persistently hot and dry, and vegetation is sparse. The dryness of the summer, what we call the “summer water deficit,” does not control the extent and severity of wildfires. Summer is almost always hot and dry enough to burn, and how much it burns depends on the amount of fuel. No matter how much hotter and drier the climate becomes, wildfire is not going to increase unless more fuel appears on the landscape. Unfortunately, <a href="https://doi.org/10.2111/REM-D-09-00151.1">exotic grasses that are adapted to wildfire</a> are invading much of the American Southwest, including the Sonoran Desert, providing that extra fuel.</p>
<p>At the other extreme are mountain forests, such as Yellowstone National Park and the surrounding area, that have abundant vegetation and fuel and are cooler and wetter. There, the amount of land that burns is strongly related to the summer water deficit. Hotter and drier summers are likely to increase wildfire activity.</p>
<p>What about areas in between these two extremes?</p>
<h2>Where hotter and drier can eventually mean less fire</h2>
<p>In California, wildfires in the dry forests of the Sierra Nevada are partly controlled by summer water deficit. For a while, hotter and drier summers are likely to increase the amount of land burned each year. </p>
<p>We ran <a href="http://doi.org/10.1002/ecs2.3657">computer simulations</a> of the interactions among climate, plant growth and wildfire for one area within the Sierra Nevada. In the first decade of the simulations, an initial burst of large areas burned each year. This first pulse of wildfire burned more area in a scenario with increased drought and temperature than in the historical climate, just as we are seeing in the recent extreme fire seasons in the Sierra Nevada. </p>
<p>Over time, however, climate change will modify how plants grow. Persistently hotter and drier climate over decades will increase <a href="https://doi.org/10.1126/science.1165000">the number of dead and dying trees</a> and <a href="https://doi.org/10.1038/ngeo1571">decrease new growth</a>. Eventually less fuel is available to burn as the dead trees decompose and fewer live ones replace them. </p>
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<p>The same computer simulations show that the initial pulse of wildfires removes a lot of dense vegetation, and subsequent fires become smaller compared with fires in historical climate conditions and with increased drought and temperature. Furthermore, because hotter and drier conditions can eventually lead to less fuel development, the wildfire area burned over 60 years <a href="https://doi.org/10.1002/ecs2.3657">may be smaller</a> with increased drought and temperature than in the historical climate. </p>
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<p>Less wildfire due to climate change may sound like good news, but how it occurs is not necessarily a desirable outcome for these forests. In the simulations, reduced wildfire is a consequence of extreme water limitation that results in reduced forest biomass. This means less tree growth and more dying trees that eventually result in a thinner and less productive forest. If the climate changes enough, the trees may even be replaced by shrubs, which have their own unique relationship between climate and wildfire.</p>
<h2>The problem with quickly putting out every fire</h2>
<p>Human actions, in particular <a href="https://academic.oup.com/jof/article-abstract/92/1/39/4635874">putting out every fire</a>, have changed how dry forests burn. </p>
<p>Some fires are started by lightning, but Indigenous peoples burned the landscape frequently, reducing fuels, so the spread and intensity of subsequent wildfires was more limited. After European colonization, the U.S. government spent more than a century actively suppressing wildfires. As a result, many forests became choked with excess fuels. Even without climate change, excess fuels <a href="https://onlinelibrary.wiley.com/doi/toc/10.1002/(ISSN)1939-5582.climate-change-and-westernwildfires">increase the wildfire hazard</a>. </p>
<p>The effect of that fire suppression on current wildfire hazards can also vary from region to region. </p>
<p>In cooler and wetter areas, <a href="https://doi.org/10.1088/1748-9326/abd78e">climate change can have a stronger effect</a> on wildfires than fire suppression. These are the areas with naturally abundant fuel and strong relationships between climate and wildfire. In drier systems, where fuels were historically low and had limited wildfire spread, suppression over the past century can have a stronger effect on current wildfire hazard than in wetter areas. It is important to consider climate change, regional characteristics and land management, all of which affect the fuels that are available to burn in a wildfire.</p>
<h2>What to do about wildfire</h2>
<p>There is no single solution to the increasing wildfire activity and declining health of forests.</p>
<p>The global solution would be to slow and eventually reverse climate change. More locally, combining prescribed fires, which are intentionally set in relatively mild weather conditions, with mechanical removal of small trees and ground fuels is the best way to <a href="https://doi.org/10.1016/j.foreco.2016.05.021">prevent more severe wildfires</a>.</p>
<p><a href="https://theconversation.com/how-years-of-fighting-every-wildfire-helped-fuel-the-western-megafires-of-today-163165">Increasing the use of prescribed fire or allowing wildfires to burn</a> under safe conditions can restore some forests to be more resilient – those that have excess fuel from fire suppression – and reduce the hazards that the western U.S. is seeing now. Past wildfires can limit the spread of new wildfires by reducing the amount of vegetation and fuel available to burn.</p>
<p><img src="https://cdn.theconversation.com/static_files/files/1737/AnnualFiresCumulate.gif?1627675461" width="100%"> </p><figure><figcaption><span class="caption">Wildfire burn perimeters near Yosemite National Park, Calif., 2000-2019. The largest is the 2013 Rim Fire. <a href="https://www.mtbs.gov/">MTBS</a></span></figcaption></figure><p></p>
<p>Over the past five years, wildfires in the U.S. burned an <a href="https://www.nifc.gov/sites/default/files/document-media/SuppCosts.pdf">average of 7.8 million acres annually</a>, which cost an average of US$2.4 billion per year to fight. </p>
<p>Managing forests in the face of the threat of larger, more severe wildfires in a warming climate presents a huge challenge to fire managers, given the costs of treatments and the <a href="https://doi.org/10.5849/jof.16-067">millions of acres that could benefit from them</a>. Plenty of wildland is still <a href="https://doi.org/10.1890/ES15-00294.1">primed to burn</a>, and understanding the intricate relationship among climate, fuels and wildfire can help managers prioritize areas where more fire will be beneficial and areas where different approaches may be preferred.</p>
<p>[<em>Understand new developments in science, health and technology, each week.</em> <a href="https://theconversation.com/us/newsletters/science-editors-picks-71/?utm_source=TCUS&utm_medium=inline-link&utm_campaign=newsletter-text&utm_content=science-understand">Subscribe to The Conversation’s science newsletter</a>.]</p><img src="https://counter.theconversation.com/content/165352/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Maureen C Kennedy receives funding from the National Science Foundation and the US Forest Service. </span></em></p><p class="fine-print"><em><span>Don McKenzie received funding from the US Forest Service. </span></em></p><p class="fine-print"><em><span>Jeremy Littell receives funding from the United States Geological Survey. </span></em></p>Not all forests respond to hotter and drier conditions in the same way.Maureen C Kennedy, Assistant Professor of Quantitative Fire Ecology, University of WashingtonDon McKenzie, Professor of Environmental and Forest Sciences, University of WashingtonJeremy Littell, Research Ecologist - Climate Impacts, US Geological SurveyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1465322020-10-13T13:28:04Z2020-10-13T13:28:04ZRestoring California’s forests to reduce wildfire risks will take time, billions of dollars and a broad commitment<figure><img src="https://images.theconversation.com/files/361799/original/file-20201006-16-342db2.jpg?ixlib=rb-1.1.0&rect=7%2C0%2C5296%2C2982&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A mixed-conifer forest in the central Sierra Nevada after restoration, with unthinned forest in the background.</span> <span class="attribution"><span class="source">Roger Bales</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span></figcaption></figure><p>As California contends with its <a href="https://news.bloomberglaw.com/environment-and-energy/californias-worst-wildfire-season-ever-is-about-to-get-uglier">worst wildfire season in history</a>, it’s more evident than ever that land management practices in the state’s forested mountains need major changes. </p>
<p>Many of California’s 33 million acres of forests face widespread threats stemming from past management choices. Today the U.S. Forest Service estimates that of the 20 million acres it manages in California, <a href="https://www.fs.usda.gov/detail/r5/landmanagement/?cid=stelprdb5412095">6-9 million acres need to be restored</a>. </p>
<p><a href="https://www.fs.usda.gov/treesearch/pubs/22209">Forest restoration</a> basically means removing the less fire-resistant smaller trees and returning to a forest with larger trees that are widely spaced. These stewardship projects require partnerships across the many interests who benefit from healthy forests, to help bring innovative financing to this huge challenge.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/362782/original/file-20201009-23-15jzgls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Thinned and unthinned forest." src="https://images.theconversation.com/files/362782/original/file-20201009-23-15jzgls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/362782/original/file-20201009-23-15jzgls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/362782/original/file-20201009-23-15jzgls.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/362782/original/file-20201009-23-15jzgls.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/362782/original/file-20201009-23-15jzgls.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/362782/original/file-20201009-23-15jzgls.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/362782/original/file-20201009-23-15jzgls.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">Treated forest (left) and untreated forest (right), central Sierra Nevada. Note the prevalence of small trees and higher density of stems on the right, and the openings between trees on the left.</span>
<span class="attribution"><span class="source">Martha Conklin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>We are engineers who work on many <a href="https://scholar.google.com/citations?user=S2cxf2IAAAAJ&hl=en">natural</a> <a href="https://scholar.google.com/citations?user=j3xbtKsAAAAJ&hl=en">resource</a> challenges, including forest management. We’re encouraged to see California and other western states striving to use forest management to reduce the risk of high-severity wildfire. </p>
<p>But there are major bottlenecks. They include scarce resources and limited engagement between forest managers and many local, regional and state agencies and organizations that have roles to play in managing forests. </p>
<p>However, some of these groups are forming local partnerships to work with land managers and develop innovative financing strategies. We see these partnerships as key to increasing the pace and scale of forest restoration.</p>
<h2>Dry, crowded forests</h2>
<p>Many conifer forests in the western United States <a href="https://doi.org/10.1016/j.foreco.2013.09.041">contain too many trees</a>, packed too closely together. This crowding is a result of past <a href="https://doi.org/10.1002/eap.1622">management practices that suppressed wildfires</a> and prioritized timber harvesting. In recent years, climate warming, accumulation of dead wood on the forest floor and a buildup of small trees – which serve as “ladder fuels,” moving fire from the forest floor up into the canopy – have led to <a href="https://theconversation.com/climate-change-and-forest-management-have-both-fueled-todays-epic-western-wildfires-146247">hotter, larger wildfires</a>. </p>
<p>Under contemporary conditions, trees in California’s forests experience increased competition for water. The exceptionally warm <a href="https://www.ppic.org/publication/californias-latest-drought/">2011-2015 California drought</a> contributed to the death of over 100 million trees. As the <a href="https://doi.org/10.1038/s41561-019-0388-5">forest’s water demand</a> exceeded the amount available during the drought, water-stressed trees succumbed to insect attacks.</p>
<p>Funding is a significant barrier to scaling up treatments. Nearly half of the Forest Service’s annual budget is <a href="https://theconversation.com/a-perfect-storm-of-factors-is-making-wildfires-bigger-and-more-expensive-to-control-100800">spent on fighting wildfires</a>, which is important for protecting communities and other built infrastructure. But this means the agency can restore only a fraction of the acres that need treatment each year.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/362348/original/file-20201008-22-1u7fagv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="Forest in mountainous area encroaching close to homes." src="https://images.theconversation.com/files/362348/original/file-20201008-22-1u7fagv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/362348/original/file-20201008-22-1u7fagv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/362348/original/file-20201008-22-1u7fagv.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/362348/original/file-20201008-22-1u7fagv.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/362348/original/file-20201008-22-1u7fagv.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/362348/original/file-20201008-22-1u7fagv.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/362348/original/file-20201008-22-1u7fagv.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">Overstocked forests, particularly around communities like this one in the northern Sierra Nevada, pose a high risk of high-severity wildfire.</span>
<span class="attribution"><span class="source">Martha Conklin</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>The benefits of restoration</h2>
<p>Forest restoration provides many benefits in addition to reducing the risk of high-severity wildfires. It reduces tree deaths and provides a foundation for sustaining <a href="https://forest-atlas.fs.fed.us/benefits-carbon-stocks.html">carbon stored in trees and soil</a>. Removing trees <a href="https://doi.org/10.1016/j.jhydrol.2020.125364">reduces water use in the forest</a>, making more water available for the remaining trees, for in-stream flows and for food production and urban areas downstream. </p>
<p>Increased streamflow also enhances electricity generation from hydropower plants, offsetting use of fossil fuels to produce electricity and contributing to state <a href="https://ww2.arb.ca.gov/our-work/programs/ab-32-climate-change-scoping-plan">greenhouse gas reduction initiatives</a>.</p>
<p>Restoring forests reduces the erosion that often follows wildfires when rain loosens exposed soil, damaging roads, power lines and ecosystems and depositing sediments in reservoirs. And it improves rural mountain economies by supporting local jobs. </p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/PzQeyu-ZIjg?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">The French Meadows Forest Restoration Project is an innovative public-private partnership to improve watershed health and restore the landscape’s historic fire regime.</span></figcaption>
</figure>
<p>Mountain headwater forests are an integral part of California’s <a href="https://leginfo.legislature.ca.gov/faces/billCompareClient.xhtml?bill_id=201520160AB2480">water infrastructure</a>. They store winter snow and rain and release moisture slowly to rivers for downstream irrigation and municipal supplies during the state’s dry summers. That’s why supporting forest restoration is also gaining traction with <a href="https://www.acwa.com/resources/improved-management-of-californias-headwaters">downstream water and hydropower providers</a>.</p>
<p>Residents across the western U.S. had weeks of unhealthy air this summer owing to smoke from wildfires. Short of curbing climate change that is <a href="https://theconversation.com/climate-change-and-forest-management-have-both-fueled-todays-epic-western-wildfires-146247">making forests more flammable</a>, reducing fuels is the best tool to lower smoke emissions. </p>
<p>Like many others, we both find that spending time in mountain conifer forests is a great <a href="https://www.penguinrandomhouse.com/books/579709/forest-bathing-by-dr-qing-li/9780525559856">source of renewal</a>. We believe that many people who live in, visit, or wish to sustain healthy mountain forests would be willing to support public investments in forest restoration. </p>
<p>Finding ways to monetize the value of less obvious benefits, such as ecological health and biodiversity, could help drive that investment. </p>
<h2>Expanding partnerships</h2>
<p>What’s the best way to create more public-private partnerships to scale up forest restoration? Two current ventures in the <a href="https://www.nature.org/content/dam/tnc/nature/en/photos/FMPFactsheet2-27-19final.pdf">American</a> and <a href="https://yubariver.org/n-yuba-forest-partnership/">Yuba</a> river basins of the central Sierra Nevada offer <a href="https://www.scienceforconservation.org/products/restoring-forests-through-partnership">lessons to build on</a>. </p>
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<p>First, it takes a dozen or more dedicated partners to plan, fund and carry out these projects. Under contracts called stewardship agreements, the Forest Service – which owns the land – does the environmental assessment and provides oversight. Project partners plan, carry out and finance forest treatments. </p>
<p>Second, depending on what kind of treatment they use, restoration can cost from US$700 to $4,000 per acre. This funding may come from state grants, foundation grants and loans, timber revenue or local agency contributions. Local agencies may repay loans with water and hydropower revenues. </p>
<p>Third, a major restoration project may stretch over five to 10 years and involve water agencies, county governments, the Forest Service, nongovernmental organizations, state agencies and the <a href="https://california-ecosystem-climate.solutions">University of California</a>.</p>
<p>Doing a project right involves much more than just cutting trees. From our experience, there are three key ingredients: accurate data for planning restoration treatments; credible methods for projecting and verifying the benefits that these treatments will produce; and incentives to bring parties together for the duration of the project.</p>
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<h2>Building public support</h2>
<p>Current projects in California have relied heavily on state grants. Going forward, the state will need more funding sources to match the goal in an August 2020 <a href="https://www.gov.ca.gov/wp-content/uploads/2020/08/8.12.20-CA-Shared-Stewardship-MOU.pdf">Shared Stewardship agreement</a> in which California and the Forest Service set a target of treating 1 million acres per year for 10 years.</p>
<p>At even $1000 per acre, treating 1 million acres will cost $1 billion per year. This figure does not include repeating treatments as forests regrow, which will be required in many areas to eventually restore a natural fire regime.</p>
<p>California is increasing the pace and scale of forest restoration, but needs to step up this effort considerably. Gov. Gavin Newsom’s new <a href="https://www.gov.ca.gov/2020/10/07/governor-newsom-launches-innovative-strategies-to-use-california-land-to-fight-climate-change-conserve-biodiversity-and-boost-climate-resilience/">Executive Order</a> to use California land to fight climate change, conserve biodiversity and boost climate resilience signals a strong intent, but meeting this multi-billion-dollar challenge will require more partners. We also see an important role for organizations working to educate and engage larger segments of the public through news stories, <a href="https://www.beyondthebrink.global/">films</a>, social media and agency outreach.</p>
<p>A warming climate is intensifying risks to forests that are already stressed by wildfires, drought and pests. Sustaining California’s iconic mountain forests requires acknowledging the multiple values they provide, and including the many groups who benefit from them in finding and implementing solutions.</p><img src="https://counter.theconversation.com/content/146532/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Roger Bales receives research support from and consults for Blue Forest and for The Nature Conservancy. Both are non-profit conservation organizations implementing forest-restoration projects in California, He also receives research support from state and federal agencies. </span></em></p><p class="fine-print"><em><span>Martha Conklin receives research support from state and federal agencies.</span></em></p>Restoring western forests – thinning out small trees and dead wood – is an important strategy for reducing the risk of massive wildfires. But these projects aren’t fast, easy or cheap.Roger Bales, Distinguished Professor of Engineering, University of California, MercedMartha Conklin, Professor of Engineering, University of California, MercedLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1214062019-08-08T13:11:36Z2019-08-08T13:11:36ZClimate change will mean more multiyear snow droughts in the West<figure><img src="https://images.theconversation.com/files/287234/original/file-20190807-144843-1oaohbt.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A valuable resource: Snowpack on Oregon's Mt. Hood.</span> <span class="attribution"><a class="source" href="https://flic.kr/p/qLSJBo">USDA NRCS/Spencer Miller</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p>As an <a href="https://scholar.google.com/citations?user=NpvW4oYAAAAJ&hl=en">environmental scientist</a>, I’ve done plenty of hiking in the western U.S. – always with a map, water bottle and list of water sources. In dry areas it’s always smart to ration water until you get to a new source. Sometimes a stream has dried up for the season, or a pond is too scummy to drink from, so your supply has to stretch further than planned.</p>
<p>On one memorable hike, I found that a water source was dry. The next one, three miles later, was dry too. And the one after that had a dead bear carcass in it. While one dry water source was tolerable, several in a row created a serious problem. </p>
<p>Something similar is happening to snow resources in the western United States. Scientists have long known that the warming temperatures associated with climate change are <a href="https://doi.org/10.1038/nature04141">diminishing</a> <a href="https://doi.org/10.1175/BAMS-86-1-39">the region’s</a> <a href="https://doi.org/10.1038/s41612-018-0012-1">snowpack</a>, with more precipitation falling as <a href="https://doi.org/10.1002/2014GL060500">rain, rather than snow</a>. That’s a problem because snowpack is a critical resource, acting as a natural reservoir that stores winter precipitation.</p>
<p>In a newly published study, my colleagues <a href="https://scholar.google.com/citations?user=S1J4kAoAAAAJ&hl=en">John Abatzoglou</a>, <a href="https://scholar.google.com/citations?user=J5v6XjUAAAAJ&hl=en">Timothy Link</a>, <a href="https://sites.google.com/site/christopherjtennanthomepage/">Christopher Tennant</a> and I analyze year-to-year variations of future snowpack to see how frequently western states can expect multiple years in a row of <a href="https://www.drought.gov/drought/data-maps-tools/snow-drought">snow drought</a>, or very low snow. We find that if climate change continues relatively unabated, consecutive years with snow drought conditions will <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL083770">become much more common</a>, with impacts on cities, agriculture, forests, wildlife and winter sports.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/ro_qgXwPVzI?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">False-color imaging shows changes in snowpack (red) in California’s Sierra Nevada over the past 20 years.</span></figcaption>
</figure>
<h2>Snow droughts affect ecoystems and people</h2>
<p><a href="https://www.watercalculator.org/water-use/importance-mountain-snowpack-water/">Snowpack</a> is a critical resource in the western U.S. and Canada. Snow melts and runs off in spring and summer, when cities, farms and forests need water. It supports animals such as <a href="https://www.fs.usda.gov/treesearch/pubs/34712">wolverines</a> that depend on snow, and underpins winter sports industries. </p>
<p>Multiyear snow droughts are akin to drawing down a bank account for some of these important systems. For example, lower snow years typically have longer summer periods with low soil moisture. Trees and other plants may be able to survive these stresses for one year, but longer stretches could lead to <a href="https://doi.org/10.1038/s41561-019-0388-5">increases in forest mortality</a>.</p>
<p>These periods also test western reservoirs, many of which are managed for dual purposes: Storing spring runoff for times of high water demand, and holding space for potential floodwaters. The amount of space allocated to storage versus flood control varies by time of year. </p>
<p>Water managers may need to update these rules to account for higher chances of snow drought or changes in the timing of snowmelt runoff. Rainfall is also a factor, and at least in California, total precipitation is projected to become <a href="https://doi.org/10.1038/s41558-018-0140-y">increasingly variable</a> from year to year with climate change. </p>
<p>Snow droughts also affect the winter tourism industry. Ski resorts in lower-elevation areas with increasingly warm winters may be able to survive one year of poor snow conditions, but multiple low-snow years in a row may threaten their viability.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/287232/original/file-20190807-144873-o9opf6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/287232/original/file-20190807-144873-o9opf6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/287232/original/file-20190807-144873-o9opf6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=454&fit=crop&dpr=1 600w, https://images.theconversation.com/files/287232/original/file-20190807-144873-o9opf6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=454&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/287232/original/file-20190807-144873-o9opf6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=454&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/287232/original/file-20190807-144873-o9opf6.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=571&fit=crop&dpr=1 754w, https://images.theconversation.com/files/287232/original/file-20190807-144873-o9opf6.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=571&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/287232/original/file-20190807-144873-o9opf6.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=571&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Frank Gehrke, chief of the California Cooperative Snow Surveys Program, carries a snow pack measuring tube near Echo Summit, Calif., on April 1, 2015 – the first time Gehrke found no snow at this location on this date.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/California-Drought-Dismal-Snowpack/a262a5dd11e44b9bacb89e86a7025aef/179/0">AP Photo/Rich Pedroncelli</a></span>
</figcaption>
</figure>
<h2>Projecting future snows</h2>
<p>In our study we defined snow droughts as years with snowpack low enough to have historically occurred only one out of every four years or less. Such events occurred recently in the <a href="https://doi.org/10.1175/EI-D-17-0027.1">Sierra Nevada between 2012-2015</a> and the <a href="https://doi.org/10.1088/1748-9326/11/8/084009">Cascades in 2014-2015</a>. </p>
<p><a href="https://climate.northwestknowledge.net/IntegratedScenarios/contact.php">Researchers</a> created the <a href="https://climate.northwestknowledge.net/IntegratedScenarios/">dataset we used</a> by first running 10 <a href="https://www.climate.gov/maps-data/primer/climate-models">global climate models</a> – computer programs that simulate historical and future climate based on a number of factors, including atmospheric carbon dioxide concentrations. </p>
<p>Like all climate projections, our estimates include some uncertainty. Each global climate model produces slightly different results; by analyzing all 10, we can be more confident in our conclusions when most of them agree on projected changes. </p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1012100762900389888"}"></div></p>
<p>These models produce data with a resolution of hundreds of kilometers. That doesn’t provide detailed information about conditions in the mountainous parts of the western U.S., where conditions vary dramatically over much smaller scales. To solve this problem, the modelers used a process called <a href="http://www.climatologylab.org/maca.html">downscaling</a> to develop results with much higher spatial resolution – in this case, to grid cells that measured about six kilometers on a side. </p>
<p>Then they loaded this climate data into a <a href="https://vic.readthedocs.io/en/master/">hydrologic model</a> that estimates daily snow accumulation and melt. We used the results from this hydrologic model to calculate changes in snowpack in future conditions, relative to historical conditions. </p>
<h2>Fewer big snow years</h2>
<p>Today, back-to-back snow droughts in the western U.S. occur around 7% of the time. By mid-century, if greenhouse gas emissions continue to increase, our results predict that multiyear snow droughts will occur in <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL083770">42% of years on average</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/287251/original/file-20190807-144862-fam407.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/287251/original/file-20190807-144862-fam407.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/287251/original/file-20190807-144862-fam407.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=600&fit=crop&dpr=1 600w, https://images.theconversation.com/files/287251/original/file-20190807-144862-fam407.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=600&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/287251/original/file-20190807-144862-fam407.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=600&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/287251/original/file-20190807-144862-fam407.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=754&fit=crop&dpr=1 754w, https://images.theconversation.com/files/287251/original/file-20190807-144862-fam407.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=754&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/287251/original/file-20190807-144862-fam407.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"></a>
<figcaption>
<span class="caption">Under a high-emission scenario, the West could experience multiyear snow drought 42% of the time on average.</span>
<span class="attribution"><a class="source" href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2019GL083770">Marshall et al., 2019.</a>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<p>In addition to projecting more frequent snow droughts, we also found that peak snowpack is projected to decline and become less variable in a warming climate across much of the mountainous West. This will mean there will be fewer very high-snow years to offset the impacts of low-snow years. </p>
<p>Another feature of changing snowpack is the timing of when it accumulates and melts. Generally, as the climate warms snow is melting earlier, which leads to earlier <a href="https://doi.org/10.1175/JCLI3321.1">spring</a> <a href="https://doi.org/10.1023/B:CLIM.0000013702.22656.e8">runoff</a> and <a href="https://doi.org/10.1002/2015GL065855">less</a> <a href="https://doi.org/10.1029/2018WR023087">water</a> available in summer. </p>
<p>In our study, we also found that in many places the timing of peak snowpack is projected to become more variable from year to year. We developed an <a href="https://snowvariability.nkn.uidaho.edu/">interactive tool</a> that allows users to explore this data on their own. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/287229/original/file-20190807-144851-1ye6mc2.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/287229/original/file-20190807-144851-1ye6mc2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/287229/original/file-20190807-144851-1ye6mc2.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=499&fit=crop&dpr=1 600w, https://images.theconversation.com/files/287229/original/file-20190807-144851-1ye6mc2.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=499&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/287229/original/file-20190807-144851-1ye6mc2.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=499&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/287229/original/file-20190807-144851-1ye6mc2.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=627&fit=crop&dpr=1 754w, https://images.theconversation.com/files/287229/original/file-20190807-144851-1ye6mc2.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=627&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/287229/original/file-20190807-144851-1ye6mc2.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=627&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Screenshot of interactive data visualization tool developed for the snow drought study.</span>
<span class="attribution"><span class="source">Adrienne Marshall</span>, <a class="license" href="http://creativecommons.org/licenses/by-nd/4.0/">CC BY-ND</a></span>
</figcaption>
</figure>
<h2>Planning for the future</h2>
<p>Our results are based on a future in which the world continues to rely on fossil fuels. Reducing greenhouse gas emissions would limit the impacts on western snowpack that we project. </p>
<p>On the hike where all of my water sources were dry, I was saved by a kind stranger. The trail intersected a road, and a passing driver gave me some water. Global climate change won’t be solved so easily: Addressing these issues will require major coordinated efforts to limit future warming and manage Earth’s natural resources strategically to provide for society’s needs and environmental conservation.</p><img src="https://counter.theconversation.com/content/121406/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Adrienne Marshall receives funding from the National Science Foundation. </span></em></p>New research forecasts that climate change will make multiyear stretches with low snow levels more common across western North America – bad news for water managers, farmers, foresters and skiers.Adrienne Marshall, Postdoctoral Fellow in Forest, Rangeland, and Fire Sciences, University of IdahoLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/979982018-06-11T10:09:57Z2018-06-11T10:09:57ZThe hunt for life on Mars: new findings on rock ‘chimneys’ could hold key to success<p>The search for life on Mars has taken a step forward with the NASA Curiosity rover’s <a href="http://science.sciencemag.org/content/360/6393/1096">discovery</a> of organic matter on the bottom of what was once a lake. <a href="https://theconversation.com/rover-detects-ancient-organic-material-on-mars-and-it-could-be-trace-of-past-life-97755">It may once</a> have been part of an alien life form or it might have a non-biological origin – either way this carbon would have provided a food source for any organic living thing in the vicinity. </p>
<p>The discovery adds extra intrigue to NASA’s search for extra-terrestrial life forms themselves. When hunting remotely with one car-sized machine, the question is where best to focus your efforts. It makes sense to look for the same types of places we expect to find fossilised microorganisms on Earth. This is complicated by the fact that these fossils are measured in microns – mere millionths of a metre. </p>
<p>The Curiosity rover looks for certain sedimentary rocks deposited near water, as it did for the latest discovery. This is based on the latest geological advice about the best prospects. Yet which rocks to prioritise is still a matter of some debate – and it’s a question that is just as relevant to geologists trying to unlock the secrets of our own ancient world. The Earth’s rocks and fossils are the nearest thing we have to time machines. </p>
<p>For a century or so, geologists focused on a type of rock called a stromatolite – devoting long hours to crawling around in awkward spaces trying to find them. Stromatolites occur mainly in shallow water and are layered on a millimetre scale. Many of them are undoubtedly built by slimy microbial “biofilms”, but to cut a long story short we now appreciate there is more than one way to make a stripy rock – and they don’t all involve microbes. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/221981/original/file-20180606-137306-1vsbzhq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/221981/original/file-20180606-137306-1vsbzhq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221981/original/file-20180606-137306-1vsbzhq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=420&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221981/original/file-20180606-137306-1vsbzhq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=420&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221981/original/file-20180606-137306-1vsbzhq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=420&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221981/original/file-20180606-137306-1vsbzhq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=527&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221981/original/file-20180606-137306-1vsbzhq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=527&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221981/original/file-20180606-137306-1vsbzhq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=527&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Stromatolite city.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/31856336@N03/6188521133">Mike Beauregard</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>More recently geologists have become more interested in other types of rocks, including the “<a href="https://www.sciencedirect.com/topics/earth-and-planetary-sciences/black-smoker">black smoker</a>” tube-type deposits formed by hot hydrothermal water being squeezed out of the Earth’s crust in the deep sea. Slightly easier to examine are similar chimney-like formations found in certain alkaline lakes around the world. </p>
<h2>Mono Lake</h2>
<p>One place on Earth where these chimneys occur is Mono Lake in California, a vast and beautiful stretch of water several hundred miles north of Los Angeles on the eastern slope of the Sierra Nevada mountains. In October 2014, our team obtained permission from the California State Parks to examine and sample some of the calcium carbonate chimneys that have formed there.</p>
<p>The rocks, which are frequently between two and three metres tall, are very young in geological terms, usually only tens of thousands of years old. But since first being <a href="https://books.google.co.uk/books/about/Quaternary_History_of_Mono_Valley_Califo.html?id=AE7nAAAAMAAJ&redir_esc=y">described</a> by the famous American geologist Israel Russell in 1889 they have proven an excellent natural laboratory for groups of scientists trying to understand how these structures came about. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/221985/original/file-20180606-137295-11ddjcf.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/221985/original/file-20180606-137295-11ddjcf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221985/original/file-20180606-137295-11ddjcf.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=392&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221985/original/file-20180606-137295-11ddjcf.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=392&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221985/original/file-20180606-137295-11ddjcf.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=392&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221985/original/file-20180606-137295-11ddjcf.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=493&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221985/original/file-20180606-137295-11ddjcf.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=493&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221985/original/file-20180606-137295-11ddjcf.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=493&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Exploration begins.</span>
<span class="attribution"><span class="source">Alexander Brasier</span></span>
</figcaption>
</figure>
<p>Before our visit, geologists were essentially divided about these chimneys. A group we might call “pure geochemists” <a href="https://www.sciencedirect.com/science/article/pii/001670379390339X">proposed</a> they were nothing to do with microbes, but produced by calcium-rich spring waters coming into contact with the alkaline lake, with its abundance of carbonate ions. </p>
<p>A smaller opposing camp <a href="http://archives.datapages.com/data/sepm/journals/v33-37/data/034/034002/0309.htm">agreed</a> it should be possible for these structures to emerge in the way that pure geochemists were suggesting. But they pointed out that, in the few recorded observations of carbonate rocks forming at the lake in the 19th and 20th centuries, some kind of biofilm did appear to have an influence. They also cited other studies that had shown that waterborne microbes called cyanobacteria did produce slimy substances that can accumulate calcium. </p>
<p>We went to Mono Lake to find out who was right. Our six-strong expedition divided into two factions: one looked for chimneys on the lake bottom using a research boat, while the other explored the famous “tufa towers” that rise up from the lake shore. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/221983/original/file-20180606-137309-1mr6wj3.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/221983/original/file-20180606-137309-1mr6wj3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221983/original/file-20180606-137309-1mr6wj3.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=378&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221983/original/file-20180606-137309-1mr6wj3.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=378&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221983/original/file-20180606-137309-1mr6wj3.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=378&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221983/original/file-20180606-137309-1mr6wj3.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=475&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221983/original/file-20180606-137309-1mr6wj3.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=475&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221983/original/file-20180606-137309-1mr6wj3.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=475&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tufa towers on the shoreline.</span>
<span class="attribution"><span class="source">Alexander Brasier</span></span>
</figcaption>
</figure>
<p>The boat party toiled and cursed the astonishingly salty waters of the lake, while the shore party made steady progress with the invaluable assistance of local state park ranger, Dave Marquart. Their peace was interrupted only by a phone call from the stranded boaters requesting they urgently try to find someone with a four-wheel drive capable of pulling the boat back out of the water – luckily help was at hand. </p>
<p>One of the sites the shore party visited was in Marquart’s own back garden to the north-west of the lake. The rocks there were part of a set of ancient chimneys formed along a small tectonic fault. Their features suggested they had been built by microbes, but we needed to send them to a lab to be sure. </p>
<h2>Microbial ‘threads’</h2>
<p>Using an optical microscope, we were able to see dark thread-like structures entombed in slices of the rock. As we outline in our <a href="https://onlinelibrary.wiley.com/doi/full/10.1111/gbi.12292">new study</a> published in Geobiology, these “threads” are millions of fossilised photosynthesising cyanobacteria that once surrounded waters rising from a spring on the lake floor. </p>
<p>We sent the samples to Australia for further testing to establish whether the microbes played a key role in building the chimneys. This revealed surrounding patches of carbon and nitrogen, which we took to be fossilised cyanobacterial slime. This slime traps calcium and when it breaks down it creates calcium carbonate, entombing any living and dead cells in rock. </p>
<p>We found other ways in which this microbial slime had affected the fabric of the rock: grains of quartz and aluminosilicates that were clearly sand that had got stuck there, too. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/221982/original/file-20180606-137315-1fu6owr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/221982/original/file-20180606-137315-1fu6owr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/221982/original/file-20180606-137315-1fu6owr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/221982/original/file-20180606-137315-1fu6owr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/221982/original/file-20180606-137315-1fu6owr.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/221982/original/file-20180606-137315-1fu6owr.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/221982/original/file-20180606-137315-1fu6owr.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/221982/original/file-20180606-137315-1fu6owr.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">Thread-like filaments in the Mono Lake rock.</span>
<span class="attribution"><span class="source">Alexander Brasier</span></span>
</figcaption>
</figure>
<p>In short, we found evidence that cyanobacteria formed tubular mats around rising spring water in the ancient Mono Lake – probably producing the majority of the resulting chimneys there, though there may be examples of “pure geochemistry” chimneys as well. This suggests that these rock formations do indeed represent a promising and fairly large target for exploring ancient or extra-terrestrial life. </p>
<p>They have the added advantage that the calcite rocks in question are geologically quite stable. This means the fossils could potentially be preserved for a very long time – easily hundreds of millions, quite plausibly billions of years. </p>
<p>To our knowledge no chimneys have been found on Mars yet, but they are not common on Earth and there is every chance that they have a Martian equivalent. There, and on other planets and moons, we should be looking for areas with conditions as similar as possible to where these chimneys exist on Earth – volcanic rocks where spring waters might once have risen through the bedrock into an alkaline lake. Without any question, NASA’s hunt for suitable rocks on the red planet should make finding them a high priority.</p><img src="https://counter.theconversation.com/content/97998/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>Following NASA’s latest discovery of organic matter on the red planet, new findings in a salt lake in California could point to where to look for alien life.Alexander Brasier, Lecturer in Geology, University of AberdeenDavid Wacey, Australian Research Council Future Fellow, The University of Western AustraliaMike Rogerson, Senior Lecturer in Earth System Science, University of HullLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/582692016-04-22T20:26:55Z2016-04-22T20:26:55ZHas climate change really improved U.S. weather?<figure><img src="https://images.theconversation.com/files/119876/original/image-20160422-17371-pe00z3.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Flooding in Houston, April 18, 2016</span> <span class="attribution"><a class="source" href="https://www.flickr.com/photos/isfullofcrap/26439149991/in/photolist-FYT3Wm-FtHC2g-GobiEH-Ftk67K-FYuw2E-Ftk7Mi-FYuuA3-Gf1wE5-FY4VXW-FsJ5Mh-GhkxeR-FsUDLH-Ghkw82-FsJ5gC-GhkB3T-FsHqqs-Ghkyz6-FsJ6wo-GhkyaD-Gf2c5G-FsUEyz-Gf2a1m-GobhGF-GkSJjb-GoopMP-Ghkzen-Gi2ZEg-FtHAWF-FZhFVW-GoooHz-GtrLaB-GfeePf-FtqrUC-FxNt4y-FxNsX1-GnqzvK-FxZ376-FxZ33i-Gtge2p-Gtge6c-GqXUC7-GjZ8ST-FZhFXQ-Fvnc51-Fvn87w-GowEmU-GowzdC-GkThDm-Ghkvr2-Dm9JwY">Laurence Simon/Flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><p>According to a <a href="http://dx.doi.org/10.1038/nature17441">new report</a> published in “Nature” on April 20, 2016 by Patrick Egan and Megan Mullin, weather conditions have “improved” for the vast majority of Americans over the past 40 years. This, they argue, explains why there has been little public demand so far for a policy response to climate change. </p>
<p>Egan and Mullin do note that this trend is projected to reverse over the course of the coming century, and that Americans will become more concerned about climate change as they perceive more negative impact from weather. However, they estimate that such a shift may not occur in time to spur policy responses that could avert catastrophic impacts.</p>
<p>However, when we consider what Americans “prefer” with respect to weather, it is important to consider all variations in the weather – across hours, days and especially the extremes – rather than simply looking at annual averages. </p>
<p>After all, no one experiences long-term average weather, but we do increasingly experience weather extremes and their impacts on our health, safety and well-being.</p>
<p>At the <a href="https://ncar.ucar.edu/">National Center for Atmospheric Research</a>, my colleagues and I have conducted numerous studies analyzing how climate change is altering regional, national and global weather patterns. </p>
<p>Many of those studies focus on extreme events such as floods, hurricanes, heat waves and droughts because these are the weather phenomena that have major impacts and costs: they destroy crops, wreck infrastructure and threaten lives and property.</p>
<p>Analyzing the impact of climate change by focusing on average weather patterns greatly underplays climate change impacts and may make Americans dangerously complacent about how climate change is already affecting our lives.</p>
<h2>Impacts of climate extremes</h2>
<p>Egan and Mullin claim that “80 percent of Americans live in counties that are experiencing more pleasant weather than they did four decades ago.” They attribute this change to rising winter temperatures paired with summers that have not become “markedly more uncomfortable.” The result, they conclude, is that weather has shifted toward a temperate year-round climate that Americans have been demonstrated to prefer. </p>
<p>For their investigation of temperature trends, the authors looked only at the average of temperatures reported in the months of January and July. For precipitation trends, the authors looked only at annual precipitation totals and the number of days on which precipitation occurs annually. </p>
<p>But people don’t live in annual or monthly averages! </p>
<p>The effects of climate change are mainly manifested through <a href="http://www.nap.edu/catalog/21852/attribution-of-extreme-weather-events-in-the-context-of-climate-change">changes in extremes</a>, because the biggest impacts, loss of life and damage to property occur especially in those conditions that break records and go beyond previous experience. </p>
<p>But the Egan and Mullin paper does not account adequately for extremes. Moreover, it should also be noted that people care about weather year-round, not just in January or July.</p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/119899/original/image-20160422-17411-tp6uz7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/119899/original/image-20160422-17411-tp6uz7.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=344&fit=crop&dpr=1 600w, https://images.theconversation.com/files/119899/original/image-20160422-17411-tp6uz7.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=344&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/119899/original/image-20160422-17411-tp6uz7.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=344&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/119899/original/image-20160422-17411-tp6uz7.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=433&fit=crop&dpr=1 754w, https://images.theconversation.com/files/119899/original/image-20160422-17411-tp6uz7.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=433&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/119899/original/image-20160422-17411-tp6uz7.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=433&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">Warming is evident in all seasons but the most outstanding high values are for March-April-May 2012 and September-October-November 2015, not just January and July. Adapted from NOAA data.</span>
<span class="attribution"><span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>For temperature, it is fluctuations up and down around averages that draw attention and impact lives. Increasing heat waves, intensifying <a href="http://www.ncdc.noaa.gov/sotc/drought/201211">droughts</a> and expanding wildfires are taking a <a href="http://www.ncdc.noaa.gov/billions/events">ruinous toll</a>, especially in summer months. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/119895/original/image-20160422-17371-1y2zwal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/119895/original/image-20160422-17371-1y2zwal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=360&fit=crop&dpr=1 600w, https://images.theconversation.com/files/119895/original/image-20160422-17371-1y2zwal.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=360&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/119895/original/image-20160422-17371-1y2zwal.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=360&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/119895/original/image-20160422-17371-1y2zwal.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=452&fit=crop&dpr=1 754w, https://images.theconversation.com/files/119895/original/image-20160422-17371-1y2zwal.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=452&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/119895/original/image-20160422-17371-1y2zwal.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=452&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
<figcaption>
<span class="caption">The 2015 wildfire season was the largest in Washington state history.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/2015_Washington_wildfires#/media/File:MODIS_-_Washington_state_wildfires_2015-08-22.jpg">MODIS</a></span>
</figcaption>
</figure>
<p>The <a href="http://earthsky.org/earth/2015-worst-us-wildfire-year-on-record">wildfire season</a> is many weeks longer than it used to be. Wildfires are local, but they affect us all through smoke and air quality, insurance and fire-fighting costs. Increasing pollen, allergies and asthma also accompany warmer conditions. In 2012 the U.S. suffered <a href="http://dx.doi.org/10.1016/j.wace.2015.10.004">widespread drought</a> and its hottest year on record. </p>
<p>In the past four decades, there has been an increasing frequency of high-humidity heat waves, which are characterized by the persistence of high nighttime temperatures. When the air stays extremely warm at night, there is less overnight relief, a fact that affects the young, elderly and ill particularly. The percentage of land area in the United States with <a href="https://www3.epa.gov/climatechange/pdfs/print_heat-waves.pdf">unusually hot summer nights</a> has increased from an average under 10 percent in the 1970s to over 40 percent in recent years.</p>
<p>Yes, it is likely true that some Americans prefer warmer winter conditions. <a href="http://protectourwinters.org/">Skiers and others who love winter sports</a>, however, are not in that group, and more significantly, in many places, including California, warmer and drier winters have helped to drive <a href="http://dx.doi.org/10.1038/nclimate2657">long-term drought</a>. Last winter, for the first time in 120 years of record-keeping, the winter average minimum temperature in the Sierra Nevada mountains was <a href="http://www.water.ca.gov/news/newsreleases/2015/092915elnino.pdf">above freezing</a>. Across the state, the prior 12 months were <a href="http://www.weatherwest.com/archives/2995">the warmest on record</a>. </p>
<p>As a result, the Sierra Nevada snow pack that normally provides nearly 30 percent of California’s water stood at its lowest level in at least 500 years, despite modest increases in precipitation from the record lows of preceding years. The few winter storms of that year were warmer than average and tended to produce rain, not snow. What snow fell melted away almost immediately. </p>
<p>Warmer winters also allow insects and diseases to survive with dramatic consequences. The successful overwintering of pine beetles, for example, in the warming winters of the Rocky Mountains contributed to <a href="http://www.ucsusa.org/global_warming/science_and_impacts/impacts/climate-change-impacts-rocky-mountain-forests.html#.Vxl-0z_mkW8">the death of 46 million acres of trees</a> from 2000 through 2012. </p>
<p>Paradoxically, perhaps, in winter, warming can also create <a href="https://theconversation.com/does-global-warming-mean-more-or-less-snow-36936">increased snowfall</a>. Warmer winters reduce sea and lake ice, increasing so-called <a href="http://earthsky.org/earth/tom-niziol-explains-lake-effect-snow">lake-effect snows</a> in places like Buffalo.</p>
<p>Extremes are also the most dangerous aspect of rising sea levels. </p>
<p>For sea level, it is not the gradual increases that matter because we barely notice gradual increases in global mean sea level. Rather, it is a storm surge on top of high tide on top of the rising sea level that causes devastation, as happened in the New York area and New Jersey shore in <a href="http://dx.doi.org/10.1038/nclimate2657">Superstorm Sandy</a>. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/119897/original/image-20160422-17371-b8dtbg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/119897/original/image-20160422-17371-b8dtbg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/119897/original/image-20160422-17371-b8dtbg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/119897/original/image-20160422-17371-b8dtbg.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/119897/original/image-20160422-17371-b8dtbg.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/119897/original/image-20160422-17371-b8dtbg.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/119897/original/image-20160422-17371-b8dtbg.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 Jersey shore after Superstorm Sandy.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/quintanomedia/8505192671">Anthony Quintano</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>The same is true of rainfall. </p>
<p>It is not the number of days with gentle showers that are of concern, but the increasing trend of <a href="http://www.thenational.ae/uae/uaes-torrential-rain-brings-flooding-cancelled-flights-and-one-death">torrential downpours</a> – as witnessed just this week in Houston, where record-breaking April rains drove <a href="https://weather.com/news/news/houston-texas-deadly-severe-flooding">devastating floods</a>. </p>
<p>The fact is that over the past century the U.S. has, on average, witnessed <a href="http://nca2014.globalchange.gov/report/our-changing-climate/heavy-downpours-increasing">a 20 percent increase</a> in the amount of precipitation falling in the heaviest downpours, with a 71 percent increase in the Northeast region and a 37 percent increase in the Midwest. This surge of extreme precipitation has dramatically increased the risk of flooding, especially in the regions with the largest increases in heavy precipitation. </p>
<p>In a warming world, storms become stronger and rainfall more intense owing to more moisture residing in the warmer atmosphere. Torrential rains flooded much of <a href="http://abcnews.go.com/US/charleston-south-carolina-soaked-worst-rains-1000-years/story?id=34233408">South Carolina,</a>
for example, last October, and <a href="http://www.srh.noaa.gov/lmrfc/">Missouri</a> experienced unprecedented rains in November and December 2015, resulting in flooding along the Mississippi River. </p>
<p>In May 2015 it was <a href="https://theconversation.com/in-texas-floods-is-there-a-link-to-climate-change-42596">Texas and Oklahoma</a> that experienced record rains and flooding, perhaps influenced by the major El Niño event combined with global warming. In September 2013 it was <a href="http://dx.doi.org/10.1038/nclimate2657">Boulder</a> and the Front Range of the Rockies that suffered from major flooding arising from heavy prolonged rains. </p>
<p>These examples show that climate change makes itself felt throughout the year.</p>
<h2>Anticipating new extremes</h2>
<p>It is important to note that our cities, our agricultural system and our infrastructure are all built entirely around the weather conditions of the past. </p>
<p>In other words, changes in extreme weather, in any direction, can have a profound impact. Disaster often strikes when a threshold is crossed, and extreme events are precisely when this happens. Adding climate change to natural variability in extreme weather can become the straw that breaks the camel’s back. </p>
<p>As detailed above, extreme weather has an outsized impact on everyday life. Ignoring the impact of extreme weather in determining the trend in “pleasant” weather conditions is, I would argue, nonsensical. Indeed, the trends in heat waves, drought and extreme precipitation would all seem to indicate that the weather overall has become more unpleasant and difficult to deal with.</p><img src="https://counter.theconversation.com/content/58269/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kevin Trenberth 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 weather has an outsized impact on everyday life. Focusing on average weather patterns may make Americans dangerously complacent about how climate change is already affecting our lives.Kevin Trenberth, Distinguished Senior Scientist, National Center for Atmospheric Research Licensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/473802015-09-14T20:19:24Z2015-09-14T20:19:24ZThe 2015 Sierra Nevada snowpack is at a 500-year record low<figure><img src="https://images.theconversation.com/files/94571/original/image-20150913-19851-1g22fgs.png?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Comparison of Sierra Nevada snowpack in 2015 v 2010. </span> <span class="attribution"><span class="source">NASA/MODIS</span></span></figcaption></figure><p>In the Mediterranean climate of California, with its warm, wet winters and hot, dry summers, the snowpack in the Sierra Nevada mountains plays a critical role. It serves as a natural water storage system that feeds waterways and reservoirs during the dry summer months. </p>
<p>That’s why it was very fitting that when Governor Jerry Brown announced the first-ever <a href="https://www.gov.ca.gov/docs/4.1.15_Executive_Order.pdf">mandatory statewide water restrictions</a>, he did it from the snow-barren Phillips snow course station in the Sierra Nevada. The April 1 snowpack’s water content has been measured at this station since 1941 and has averaged at 66.5 inches over this period. On April 1 2015, there was no snow on the ground.</p>
<p>The Phillips station underscores how extreme the 2015 snowpack situation is. In our <a href="http://dx.doi.org/10.1038/nclimate2809">study</a>, we put the 2015 snowpack low in a long-term context and demonstrated that these were the driest conditions in 500 years. </p>
<p>Our research, based on tree-ring data, also suggests that in the future California officials need to alter plans for managing and storing water from the snowpack, which has historically supplied about <a href="http://www.water.ca.gov/news/newsreleases/2015/040115snowsurvey.pdf">30%</a> of the state’s water.</p>
<h2>Reconstructing past climate</h2>
<p>Our team has been working for a couple of years on reconstructing the atmospheric circulation patterns that drive hydroclimate variability over the American Pacific Coast. When the 2015 snowpack levels for the Sierra Nevada were found to be <a href="http://cdec.water.ca.gov/cgiprogs/%20snow/COURSES.04">5% of their historical average</a> on April 1 – the date when snowpack is normally at its peak – we realized that we could provide a century-scale context for these numbers. </p>
<p>We combined two independent tree-ring-based data sets representing the two primary climate components that determine snowpack levels: the amount of winter precipitation and winter temperatures. </p>
<p>As a proxy for winter precipitation over the Sierra Nevada, we used a tree-ring compilation of more than 1,500 blue oak trees in central California. The California blue oaks are some of the most moisture-sensitive trees to be found anywhere on the planet. Their tree-ring width reliably <a href="http://journals.ametsoc.org/doi/abs/10.1175/2013EI000518.1">tracks the amount of winter rainfall that central California receives</a> and the storm tracks that bring that rainfall from the Pacific Ocean. These same storm tracks, as they move farther east, then deliver winter precipitation in the form of snow over the Sierra Nevada. </p>
<p>For winter temperature, we used a tree-ring-based <a href="http://www.sciencedirect.com/science/article/pii/S0921818114001702">winter (February-March) temperature reconstruction</a> developed for and averaged over two gridpoints in central and southern California. Temperature is an important factor in year-to-year snowpack variability because it determines how much of the precipitation falls as rain versus snow and affects the speed of snowmelt.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/94681/original/image-20150914-4717-1bj5qir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/94681/original/image-20150914-4717-1bj5qir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/94681/original/image-20150914-4717-1bj5qir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/94681/original/image-20150914-4717-1bj5qir.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/94681/original/image-20150914-4717-1bj5qir.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/94681/original/image-20150914-4717-1bj5qir.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/94681/original/image-20150914-4717-1bj5qir.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/94681/original/image-20150914-4717-1bj5qir.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=501&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Tree-ring records for blue oak (Quercus douglasii), which is sensitive to winter precipitation, were used to reconstruct the Sierra Nevada snowpack over the last 500 years.</span>
<span class="attribution"><a class="source" href="https://www.flickr.com/photos/miguelvieira/2988643620/in/photolist-5y6zCh-rtUfMQ-5wrD2d-93egdq-9kieXH-34tJJX-7kynzE-5y2bLe-9xcL4f-5y2bTP-m7Xejo-iwXuMr-m7Vvck-iwWWmg-iwXAm2-7QxJmT-7QxVMX-7QxRSi-7QxUt6-9cFXLt-9dcM2z-7QB1vs-njjQ1m-7koahG-qv1jnG-qfxx2u-bNe2aa-dDQ97B-hMVwp9-2WZTkW-deYKYH-9dfTq1-rDfFK8-rDfmLX-deYHom-9duTEG-4Fm1vt-fntc7J-qmvF36-e8gpTi-5RTjuE-e4hnhV-bnDK7f-72Gacv-72Lcid-72GdQZ-8Fe9RQ-dn6x6k-72GaK8-7QB6bu">miguelvieira/flickr</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>We combined the winter precipitation and the winter temperature data sets in a model that captures how much these factors contribute to snow water equivalent (SWE) values for the April 1 Sierra Nevada-wide measurement. SWE is a widely used measure of snowpack that reflects its water content. We compiled April 1 SWE data from 108 snow course stations throughout the Sierra Nevada that started measurements in 1930 or earlier. We were surprised by how similar the SWE measurements from these 108 stations were and used this common SWE signal to calibrate our tree-ring based multiple linear regression model.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/94719/original/image-20150914-4695-z2xsf0.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/94719/original/image-20150914-4695-z2xsf0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/94719/original/image-20150914-4695-z2xsf0.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=288&fit=crop&dpr=1 600w, https://images.theconversation.com/files/94719/original/image-20150914-4695-z2xsf0.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=288&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/94719/original/image-20150914-4695-z2xsf0.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=288&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/94719/original/image-20150914-4695-z2xsf0.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=363&fit=crop&dpr=1 754w, https://images.theconversation.com/files/94719/original/image-20150914-4695-z2xsf0.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=363&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/94719/original/image-20150914-4695-z2xsf0.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=363&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Using tree-ring data, researchers were able to reconstruct precipitation and temperature patterns of the past, showing how this year’s Sierra Nevada snowpack is the lowest in 500 years. The line shows varying levels of snowpack water content.</span>
<span class="attribution"><span class="source">Soumaya Belmecheri</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Our model allowed us to reconstruct Sierra Nevada April 1 SWE back to the year 1500 CE, and we found that the 2015 April 1 SWE value was the lowest on record over this time span. We further used these 500+ years of data to estimate return periods for snowpack – that is, the likelihood of a 2015 snowpack low as this year to occur. Our results indicate that the expected return period for a 2015-level snow drought is longer than 3,000 years. This estimate has a number of uncertainties, but we can say with 95% confidence that the 2015 SWE return period is longer than the 500-year time span of our reconstruction.</p>
<h2>Differences in elevations</h2>
<p>It is important to note that this 500-year return period estimate is based on the past five centuries and cannot be extrapolated into the future. On the contrary, it is likely that the frequency of occurrence of a 2015-level snow drought will increase with anthropogenic climate change. </p>
<p>The co-occurrence of <a href="http://www.pnas.org/content/112/13/3931.short">very low winter precipitation anomalies and very high temperature anomalies</a> is needed for extreme snowpack lows. In 2015, far below normal winter precipitation in the Sierra Nevada co-occurred with record high January-March temperatures, <a href="https://theconversation.com/how-climate-change-is-making-californias-epic-drought-worse-40030">resulting in a 500-year snowpack low</a>. Future <a href="https://theconversation.com/what-historic-megadroughts-in-the-western-us-tell-us-about-our-climate-future-37615">model projections agree</a> that California temperatures will rise over the coming century, and the chance of low precipitation events co-occurring with them will thus increase. </p>
<p>In this context, we found an interesting difference between low (< ~2,130 meters or 7,000 feet) and high elevations (>~2,670 m or 8,750 ft). At low elevations, where <a href="http://onlinelibrary.wiley.com/doi/10.1029/2005JF000356/pdf">winter temperature has strong control over SWE</a>, the 2015 snow drought is strongly exceptional, with an estimated return period of longer than 1,000 years. </p>
<p>At high elevations, however, winter precipitation is the primary driver of snowpack, and the 2015 SWE value exceeds the 95% confidence level for only a 95-year return period. Knowing that the northern Sierras are typically of lower elevation than the southern Sierras, this finding has important implications for water management strategies and deserves further detailed study.</p>
<h2>Planning for the future</h2>
<p>As we are writing this piece, the <a href="http://cdfdata.fire.ca.gov/incidents/incidents_details_info?incident_id=1221">Butte fire</a> and Rough fire are raging through the Sierra Nevada, demonstrating in a devastating manner the link between <a href="http://www.sciencemag.org/content/313/5789/940.short">low snowpack, earlier spring snowmelt and increased wildfire risk</a>. </p>
<p>The impact of the 2015 snowpack low on Sierra Nevada ecosystems presents an ominous sign of the severity of the drought conditions that California has been experiencing since 2012. </p>
<p>The impacts of this drought have included water cuts for urban and agriculture consumers, drying wells for local communities and low hydroelectric power generation. Statewide water restrictions have helped to reduce these impacts, but have also revealed California’s <a href="https://theconversation.com/what-would-it-take-to-end-californias-drought-46443">vulnerability and lack of preparedness</a> to coping with these societal impacts. </p>
<p>With the Sierra Nevada snowpack historically supplying roughly 30% of California’s overall water, the 2015 snow drought helps explain the state’s <a href="https://www.gov.ca.gov/news.php?id=18368">drought state of emergency </a> because of the decimating water reservoir levels. </p>
<p>The unprecedented nature of the 2015 snow drought provides some foreshadowing for the future as well: with projected anthropogenic warming, the Sierra Nevada snowpack will be a less reliable source of water for reservoirs and suggests that adequate planning for water management and capturing is needed to build a resilient system for dire situations such as the current one.</p><img src="https://counter.theconversation.com/content/47380/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Valerie Trouet receives funding from the National Science Foundation, the Department of Energy, and the Department of the Interior Southwest Climate Science Center (U.S. Geological Survey). </span></em></p><p class="fine-print"><em><span>Soumaya Belmecheri receives funding from National Science Foundation, USGS, DoI </span></em></p>According to scientists, tree-ring analysis shows that California drought is the worst it has been in 500 years.The study underscores the severity of current drought and the challenges of future water management in the state.Valerie Trouet, Associate Professor of Dendrochronology, University of ArizonaSoumaya Belmecheri, Post-doctoral Research Associate in Paleoclimate, University of ArizonaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/423962015-07-23T09:47:47Z2015-07-23T09:47:47ZThrough the brewing class: what beer-making can teach students about business<figure><img src="https://images.theconversation.com/files/89242/original/image-20150721-24304-1xmb9ee.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">What lessons are there in the beer industry?</span> <span class="attribution"><span class="source">Rhett Brymer</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><p><em>This article is a part of The Conversation’s series on unique courses. For other articles in this series, read <a href="https://theconversation.com/philosophical-toolkit-in-tow-scholar-travels-to-conflict-zones-42805">here</a> and <a href="https://theconversation.com/a-teacher-uses-star-trek-for-difficult-conversations-on-race-and-gender-43098">here</a>.</em></p>
<p>Next time you are in your local grocery store, step in to look a little more closely at the beer cooler. Amid the brightly colored, creative packaging lies the final battle for the ultimate goal – your purchases. </p>
<p>But, what battles were fought to get the beer to that particular cooler? More importantly, what might those battles say about larger trends in business today? </p>
<p>At Miami University’s Farmer School of Business, we designed an experiential class to go in depth with these issues, leveraging the lessons of the beer industries as a way to better understand larger trends in business strategy and supply chains. </p>
<h2>What can the beer industry teach us?</h2>
<p>Why beer? What is significant about the brewing industry? And what can students take away (besides a new appreciation for hops)?</p>
<p>The beer industry turns out to be a fascinating microcosm of the larger landscape of today’s business climate. Breweries are varied and transparent, prisms through which students get to see firsthand the strategies employed by the full spectrum – from tiny nanopubs to the <a href="http://www.brewbound.com/news/the-brewers-association-top-50-u-s-craft-breweries-of-2013">fastest-growing midsized breweries</a> to the <a href="http://www.agmrc.org/media/cms/coors_6C217F1EDB6E5.pdf">largest brewing facility in the world</a>. In other words, they offer the perfect opportunity to use a hospitable, popular setting to examine a plethora of questions facing the industry and individual businesses.</p>
<p>For instance, how can microbreweries survive given their paltry market share? (The average US microbrewery has a 0.0041% market share.) Who are they? And how do they compete against the global brands and scale of the macrobreweries? </p>
<p>We set out to find out for ourselves – and for our students.</p>
<p>During a three-week intensive examination of the beer industry, we toured 25 breweries and related facilities from Portland, Oregon to Asheville, North Carolina in a field study to get to know the intimate details of the industry’s supply chain. </p>
<p>And what did we find?</p>
<p>The overwhelming majority of new market entrants in the beer industry are craft breweries that sell to a very localized consumer base. </p>
<p>As the dominant market players concentrated on general markets, widespread distribution and global uniformity, there were many <a href="https://www.gsb.stanford.edu/faculty-research/publications/why-microbrewery-movement-organizational-dynamics-resource">geographic niches</a> for entrepreneurs to claim local identities. </p>
<p>Now, the craft and local nature of these new beers is <a href="http://www.wsj.com/articles/budweiser-ditches-the-clydesdales-for-jay-z-1416784086">capturing</a> the new generation of beer drinkers – indeed, 44% of drinkers aged 21 to 27 report never tasting Budweiser or Bud Light, two macrobrew icons. </p>
<figure class="align-center ">
<img alt="" src="https://images.theconversation.com/files/89243/original/image-20150721-24266-1xscmcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/89243/original/image-20150721-24266-1xscmcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/89243/original/image-20150721-24266-1xscmcy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/89243/original/image-20150721-24266-1xscmcy.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/89243/original/image-20150721-24266-1xscmcy.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/89243/original/image-20150721-24266-1xscmcy.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/89243/original/image-20150721-24266-1xscmcy.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">
<figcaption>
<span class="caption">In touring the beer industry, students start to understand it at a deeper level.</span>
<span class="attribution"><span class="source">William Newman</span>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Instead, <a href="http://libra.msra.cn/Publication/42770013/microbreweries-as-tools-of-local-identity">drinking local beer</a> has become part political statement – lowering carbon emissions and supporting local entrepreneurs – and part cultural experience – either as connection to a hometown or as a tourist destination. </p>
<h2>Application to the future</h2>
<p>In touring a few dozen breweries, students begin to understand the industry at a much deeper level. </p>
<p>They see up close the struggles the small brewers go through to survive. They understand the challenges of scaling up and maintaining complex businesses with national distributions. They recognize strategies and the logic behind them.</p>
<p>Yet, they still have to grapple with large, unanswered questions:</p>
<blockquote>
<p>How many local breweries can the US sustain? </p>
<p>Will we see a bubble in the beer industry as more <a href="http://www.cnbc.com/id/101142795">investment money</a> pours into brewing?</p>
</blockquote>
<p>In response to declining light lager sales domestically, the major breweries have turned to acquiring smaller craft brands like 10 Barrel, Elysian and Leinenkugals, <a href="http://money.cnn.com/2015/05/15/news/companies/beer-sabmiller-meantime/">mirroring efforts</a> in the food industries as “big food” yields market share to local, niche brands.</p>
<p>Similarly, independent craft brewers, like New Belgian and Sierra Nevada, have become <a href="https://www.brewersassociation.org/insights/brewery-consolidation/">national brands</a>, bringing together the opposing forces of scale economies and local branding, replete with high connection with consumers, small batches and nimble product offerings. But can rapidly growing craft breweries keep their local feel? </p>
<p>So, some of the questions we ask are: will acquired local breweries continue having craft appeal with new macrobrewery ownership? What are the quality implications for regional craft beers once they are part of a larger company? </p>
<p>Interestingly, unlike the big companies, small beer manufacturers tend to view each other as more <a href="http://blog.stonebrewing.com/index.php/collaboration-not-competition-a-look-at-craft-beer-culture/">collaborators than competitors</a>, and openly share stories of assisting a competing brewery when in a pinch. </p>
<p>Because of the craft beer market growth, <a href="https://www.brewersassociation.org/statistics/national-beer-sales-production-data/">increasing revenue</a> at individual craft breweries has not had to come at the <a href="http://www.cnbc.com/2014/02/26/rewery-revolution-heats-up.html">expense of other craft breweries</a>. </p>
<p>Instead, thousands of craft breweries have formed alliances, such as the Brewer’s Association, to <a href="https://www.brewersassociation.org/current-issues/brewers-association-and-beer-institute-send-joint-letter-to-members-of-congress/">lobby on behalf of smaller breweries</a> to position themselves with better laws, taxes and regulations, in turn decreasing the advantages of large incumbents.</p>
<p>This leads to yet another question: will the collaborative ethos of smaller craft breweries turn ugly when craft beer sales begin to decline? </p>
<h2>What’s in a bottle of beer</h2>
<p>The bottle of beer on the grocery shelf seems so simple. Yet, it is the result of an intricate orchestration of materials and logistics that takes seeing to grasp. </p>
<p>Producing glass from train cars of sand; securing contracts for hop futures to avoid severe shortages; malting your own barley; breeding superior strains of yeast; locating plants on top of preferred aquafers: all sourcing strategies used to achieve an edge on the competition. </p>
<p>Students respond avidly when they see an industry in such great depth. They appreciate how complex running a business truly is regardless of size. </p>
<p>They are stunned at the variety of company cultures, and become more comfortable in finding one right for them. They see the fruits of an idea, an entrepreneur and hard work, compelling confidence in many students to start their own ventures. </p>
<p>Students in this class get to experience the “real stuff,” outside the sterility of a classroom, and outside their disciplinary bubbles. As prominent activist and food writer <a href="https://www.penguin.com.au/products/9781846148033/cooked-natural-history-transformation">Michael Pollan recently wrote</a>: “One of the problems with the division of labor in our complex economy is how it obscures the lines of connection.” </p>
<p>Being out in the field and being challenged with the complexities of several real businesses each day helps make those connections. So, we do these tours each year. We embark on our next field tour in January 2016.</p>
<p>Although numerous programs on the science and techniques of brewing have <a href="http://www.beeradvocate.com/community/threads/beeradvocate-magazine-98-march-2015.263602/">cropped up</a> nationwide, few have explored the breadth and depth of the business in all its intricacies and connections. </p>
<p>Single-industry classes, such as this one, allow students to see the lines of connection between business functions, across the niches of a marketplace. They also allow them to explore the complexities of supply chains and cooperative strategies that structure the modern-day economies that these graduates are entering.</p><img src="https://counter.theconversation.com/content/42396/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 organization that would benefit from this article, and have disclosed no relevant affiliations beyond their academic appointment.</span></em></p>The beer industry is a fascinating microcosm of the larger landscape of today’s business environment. Students can examine a range of questions facing businesses, through the beer industry.Rhett Andrew Brymer, Assistant Professor of Management , Miami UniversityW. Rocky Newman, Professor of Management, Miami UniversityLicensed as Creative Commons – attribution, no derivatives.