tag:theconversation.com,2011:/au/topics/hail-11737/articlesHail – The Conversation2023-05-04T14:25:46Ztag:theconversation.com,2011:article/2049752023-05-04T14:25:46Z2023-05-04T14:25:46ZCloud seeding can increase rain and snow, and new techniques may make it a lot more effective – podcast<figure><img src="https://images.theconversation.com/files/524204/original/file-20230503-19-bx8o26.jpg?ixlib=rb-1.1.0&rect=418%2C594%2C6930%2C4308&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Cloud seeding can increase rainfall and reduce hail damage to crops, but its use is limited.</span> <span class="attribution"><a class="source" href="https://www.gettyimages.com/detail/photo/colorado-supercell-royalty-free-image/1303884216?phrase=Rain+storm&adppopup=true">John Finney Photography/Moment via Getty Images</a></span></figcaption></figure><p>When an unexpected rainstorm leaves you soaking wet, it is an annoyance. When a drought leads to fires, crop failures and water shortages, the significance of weather becomes vitally important.</p>
<p>If you could control the weather, would you?</p>
<p>Small amounts of rain can mean the difference between struggle and success. For <a href="https://climateviewer.com/2014/03/25/history-cloud-seeding-pluviculture-hurricane-hacking/">nearly 80 years</a>, an approach called cloud seeding has, in theory, given people the ability to get more rain and snow from storms and make hailstorms less severe. But only recently have scientists been able to peer into clouds and begin to understand how effective cloud seeding really is.</p>
<p>In this episode of “The Conversation Weekly,” we speak with three researchers about the simple yet murky science of cloud seeding, the economic effects it can have on agriculture, and research that may allow governments to use cloud seeding in more places.</p>
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<p><a href="https://scholar.google.com/citations?user=BSQl42wAAAAJ&hl=en&oi=ao">Katja Friedrich</a>, a professor of atmospheric and oceanic sciences at the University of Colorado, Boulder in the U.S., is a leading researcher on cloud seeding. “When we do cloud seeding, we are looking for clouds that have tiny super-cooled liquid droplets,” she explains. Silver iodide is very similar in structure to an ice crystal. When the droplets touch a particle of silver iodide, “they freeze, then they can start merging with other ice crystals, become snowflakes and fall out of the cloud.”</p>
<p>While the process is fairly straightforward, measuring how effective it is in the real world is not, according to Friedrich. “The problem is that once we modify a cloud, it’s really difficult to say what would’ve happened if you hadn’t cloud-seeded.” It’s hard enough to predict weather without messing with it artificially. </p>
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<a href="https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="A plane wing with a cylindrical device attached." src="https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=370&fit=crop&dpr=1 600w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=370&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=370&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=465&fit=crop&dpr=1 754w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=465&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/524222/original/file-20230503-1294-7b7p2j.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=465&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Cloud seeding is usually done by planes equipped with devices – like the one attached to the wing of this plane – that spray silver iodide into the atmosphere.</span>
<span class="attribution"><a class="source" href="https://en.wikipedia.org/wiki/Cloud_seeding#/media/File:Hagelflieger-EDTD.jpg">Zuckerle/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>In 2017, Friedrich’s research group had a breakthrough in measuring the effect of cloud seeding. “We flew some aircraft, released silver iodide and generated these clouds that were like these six exact lines that were downstream of where the aircraft were seeding,” she says. They then had a second aircraft fly through the clouds. “We could actually <a href="https://doi.org/10.1073/pnas.1716995115">quantify how much snow we could produce</a> by two hours of cloud seeding.” That effect, according to research on cloud seeding, is an increase in precipitation of somewhere around 5% to 20% or 30%, depending on conditions.</p>
<p>Measuring the effect on precipitation – whether rain or snow – directly may have taken complex science and a bit of luck, but in places that have been using cloud seeding for long periods of time, the economic benefits are shockingly clear. </p>
<p><a href="https://www.ndsu.edu/agriculture/ag-home/directory/dean-bangsund">Dean Bangsund</a> is a researcher at North Dakota State University who studies the economics of agriculture. “We have a high amount of hail damage in North Dakota,” said Bangsund. For decades, the state government has been using cloud seeding to reduce hail damage, as cloud seeding leads to the formation of more pieces of smaller hail compared to fewer pieces of larger hail. “It doesn’t 100% eliminate hail; it’s designed to soften the impact.”</p>
<p>Every 10 years, the state of North Dakota does an <a href="https://www.cabdirect.org/cabdirect/abstract/20193399635">analysis on the economic impacts of the cloud seeding</a> program, measuring both reduction in hail damage and benefits from increased rain. Bangsund led the last report and says that for every dollar spent on the cloud seeding program, “we are looking at something that is anywhere from $8 or $9 in benefit on the really lowest scale, up to probably $20 of impact per acre.” With millions of acres of agricultural fields in the cloud seeding area, that is a massive economic benefit.</p>
<p>Both Freidrich and Bangsund emphasized that cloud seeding, while effective in some cases, cannot be used everywhere. There is also a lot of uncertainty in how much of an effect it has. One way to improve the effectiveness and applicability of cloud seeding is by improving the seed. <a href="https://scholar.google.com/citations?view_op=list_works&hl=en&hl=en&user=OxrNpiEAAAAJ&sortby=pubdate">Linda Zou</a> is a professor of civil infrastructure and environmental engineering at Khalifa University in the United Arab Emirates. </p>
<p>Her work has focused on developing a replacement for silver iodide, and her lab has <a href="https://www.technologyreview.com/2022/03/28/1048275/scientists-advance-cloud-seeding-capabilities-with-nanotechnology/">developed what she calls a nanopowder</a>. “I start with table salt, which is sodium chloride,” says Zou. “This desirable-sized crystal is then coated with a thin nanomaterial layer of titanium dioxide.” When salt gets wet, it melts and forms a droplet that can efficiently merge with other droplets and fall from a cloud. Titanium dioxide attracts water. Put the two together and you get a very effective cloud-seeding material. </p>
<p>From indoor experiments, Zou found that “with the nanopowders, there are 2.9 times the formation of larger-size water droplets.” These nanopowders can also form ice crystals at warmer temperatures and less humidity than silver iodide. </p>
<p>As Zou says, “if the material you are releasing is more reactive and can work in a much wider range of conditions, that means no matter when you decide to use it, the chance of success will be greater.”</p>
<hr>
<p>This episode was written and produced by Katie Flood. Mend Mariwany is the executive producer of The Conversation Weekly. Eloise Stevens does our sound design, and our theme music is by Neeta Sarl.</p>
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<hr><img src="https://counter.theconversation.com/content/204975/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>None of the interviewees work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.</span></em></p><p class="fine-print"><em><span> </span></em></p>Cloud seeding – spraying materials into clouds to increase precipitation – has been around for nearly 80 years. But only recently have scientists been able to measure how effective it really is.Daniel Merino, Associate Science Editor & Co-Host of The Conversation Weekly Podcast, The ConversationNehal El-Hadi, Science + Technology Editor & Co-Host of The Conversation Weekly Podcast, The ConversationLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1458952020-09-18T09:41:33Z2020-09-18T09:41:33ZDon’t write off government algorithms – responsible AI can produce real benefits<figure><img src="https://images.theconversation.com/files/358688/original/file-20200917-20-18hdkib.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">
</span> <span class="attribution"><a class="source" href="https://www.a.com/image-photo/young-business-person-graphical-user-interface-563081320">Metamorworks/Shutterstock</a></span></figcaption></figure><p>Algorithms have taken a lot of flak recently, particularly those being used by the government and other public bodies in the UK. The controversial algorithm used to award student grades caused a huge public outcry, <a href="https://www.bbc.co.uk/news/technology-53650758">but national</a> and <a href="https://www.theguardian.com/society/2020/aug/24/councils-scrapping-algorithms-benefit-welfare-decisions-concerns-bias">local governments</a> and several <a href="https://www.thetimes.co.uk/article/police-scrap-artificial-intelligence-tool-to-predict-violence-zdln8bgz0">police forces</a> have been withdrawing other algorithms and artificial intelligence tools from use throughout the year in response to legal challenges and design failures. </p>
<p>This has quite rightly brought it home to public sector organisations that a more critical approach to AI and algorithmic decision-making is needed. But there are many cases in which government bodies can deploy such technology in lower risk, high-impact scenarios that can improve lives, particularly if they don’t directly use personal data. </p>
<p>So before we leap <a href="https://unherd.com/2020/08/how-ofqual-failed-the-algorithm-test">full pelt into AI cynicism</a> we should consider benefits as well as risks it offers, and demand a more responsible approach to AI development and deployment.</p>
<p>One example of this is the <a href="https://futurecity.glasgow.gov.uk/intelligent-street-lighting/">Intelligent Street Lighting project</a> being trialled by Glasgow City Council. It uses an algorithm to process real time sensor data on noise, air pollution and footfall around the city and control street lighting in reaction to people’s use of cycle paths and open spaces. </p>
<p>The aim is to immediately improve safety but also allow for better city planning and environmental protection. Importantly, this project is being properly trialled and is open to public scrutiny, which will help address people’s concerns and needs.</p>
<p>Similarly, Liverpool City Council is working with the company Red Ninja on the <a href="https://futurecities.catapult.org.uk/cityx/artificial-intelligence-for-traffic-flow/">Life First Emergency Traffic Control</a> project, which aims to cut ambulance journey times by up to 40%. A new algorithm works within the existing traffic signal system to prioritise emergency vehicles, aiming to <a href="https://www.vice.com/en_us/article/jp3dn7/new-ai-algorithm-beats-even-the-worlds-worst-traffic">reduce congestion</a> ahead of emergency vehicles and save critical minutes on ambulance response times.</p>
<p><a href="https://www.govtech.com/civic/GT-September-Automation-Beyond-the-Physical-AI-in-the-Public-Sector.html">Governments can also use AI</a> for many low-risk jobs which do not directly aim to predict human behaviour or make decisions directly affecting individuals. For example, <a href="https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/871178/A_guide_to_using_AI_in_the_public_sector__web_version_.pdf">National Grid uses AI</a> and drones to inspect 7,200 miles of overhead power lines in England and Wales. </p>
<p>It is are able to assess the steelwork, wear and corrosion and faults to conductors. This speeds up inspection, saving time and money and allows human engineers to focus on repairs and improvements, producing a more reliable energy supply.</p>
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<img alt="Drone hovers near electricity pylon" src="https://images.theconversation.com/files/358690/original/file-20200917-16-1fy2eau.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/358690/original/file-20200917-16-1fy2eau.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/358690/original/file-20200917-16-1fy2eau.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/358690/original/file-20200917-16-1fy2eau.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/358690/original/file-20200917-16-1fy2eau.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/358690/original/file-20200917-16-1fy2eau.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/358690/original/file-20200917-16-1fy2eau.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">
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<span class="caption">AI can power automation of difficult jobs.</span>
<span class="attribution"><a class="source" href="https://www.shutterstock.com/image-photo/drone-transmission-towers-742893928">KOHUKU/Shutterstock</a></span>
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<p>The Driver and Vehicle Standards Agency (DVSA) <a href="https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/871178/A_guide_to_using_AI_in_the_public_sector__web_version_.pdf">has used AI to improve MOT testing</a> by using AI to analyse the vast amount of testing data to develop risk scores for garages and identify potentially underperforming centres. This has reduced enforcement visits by 50%. </p>
<p>The counterpart Driver and Vehicle Licensing Agency (DVLA) <a href="https://www.gov.uk/government/case-studies/how-the-dvla-deployed-a-chatbot-and-improved-customer-engagement">used a natural language processing algorithm</a> to develop <a href="https://theconversation.com/emotionless-chatbots-are-taking-over-customer-service-and-its-bad-news-for-consumers-82962">a chatbot</a> to deal with customer enquiries. This is integrated into a single customer service platform so that staff can monitor all customer interactions by phone, email, webchat and social media. </p>
<p>These examples show the potential for government to use AI successfully and responsibly. So how can public sector bodies ensure their algorithms manage this? </p>
<p>To begin with, there are numerous sets of guidelines they can follow, such as the <a href="https://www.oecd.org/going-digital/ai/principles/">OECD Principles on AI</a>.
These principles state that AI should be designed in a way that respects human rights, democratic values and diversity and include appropriate safeguards and monitoring of risks. There is a requirement for transparency and responsible disclosure so people understand the systems and can challenge them.</p>
<p>But guidelines aren’t necessarily enough. The UK government has published its own <a href="https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/871178/A_guide_to_using_AI_in_the_public_sector__web_version_.pdf">guidelines for trustworthy use of AI</a>, and has invested significantly in <a href="https://www.gov.uk/government/groups/ai-council">numerous</a> <a href="https://www.gov.uk/government/organisations/office-for-artificial-intelligence">expert</a> AI <a href="https://www.gov.uk/government/organisations/centre-for-data-ethics-and-innovation">advisory</a> <a href="https://www.gov.uk/government/groups/regulatory-horizons-council-rhc">bodies</a>. Yet it has still managed to get many things wrong in its development of algorithms, as recent events have shown. </p>
<p>One reason for this is that there is little acceptance even now that AI technology is not good enough to safely be used on high-impact and high-risk cases, such as awarding grades and visas. Sometimes AI should not be a solution.</p>
<h2>Laws and nudges</h2>
<p>New laws regulating the use of AI could help, but few countries have yet to pass specific legislation. There are some good examples in development, such as the proposed US <a href="https://www.technologyreview.com/2019/04/15/1136/congress-wants-to-protect-you-from-biased-algorithms-deepfakes-and-other-bad-ai/">AI Accountability Bill</a>. However, legislation moves slowly, is subject to significant lobbying and outstripped by the speed of tech innovation. So quicker nudges to responsible behaviour are needed.</p>
<p>The recent abandoning of certain government algorithms have shown that when the public is aware of poorly developed AI it can change government behaviour and create demand for more trustworthy use of technology. So one possible solution, called for by the researcher network Women Leading in AI, of which I am a founder, is an <a href="https://womenleadinginai.org/report2019">AI Infomark</a>.</p>
<p>Any apps, websites or documents relating to government services, systems or decisions that use AI would display the mark to alert people of that fact and point them to information about how the AI works and its potential impact and risk. This is a citizen-first strategy designed to empower people to understand and challenge an algorithm or AI system that has affected them. And this should hopefully push government to make sure it gets things right in the first place.</p>
<p>If government can combine adequate regulation with this kind empowering, bottom-up approach to ensuring more responsible technology, we can start to reap the real benefits of greater use of algorithms and AI.</p><img src="https://counter.theconversation.com/content/145895/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Allison Gardner is affiliated with Women Leading in AI, IEEE, Labour Digital, For Humanity, We and AI and Intelligent Health. </span></em></p>Despite the exams algorithm fiasco, UK government bodies are making positive uses of the technology.Allison Gardner, Lecturer in Computer Science/Co-founder Women Leading in AI, Keele UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1445352020-09-03T15:18:06Z2020-09-03T15:18:06ZExtreme precipitation events have always occurred, but are they changing?<figure><img src="https://images.theconversation.com/files/355354/original/file-20200828-23-g3r8ld.jpg?ixlib=rb-1.1.0&rect=77%2C83%2C3910%2C2149&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">A woman wades into flood waters in Calgary, Alta., on June 14, 2020, after a major hail storm damaged homes and flooded streets.</span> <span class="attribution"><span class="source">THE CANADIAN PRESS/Jeff McIntosh</span></span></figcaption></figure><p>Extreme weather and climate events causing extensive damage are a fact of the Canadian climate, and this year is no exception. </p>
<p>On June 13, a <a href="https://globalnews.ca/news/7204802/calgary-june-13-hailstorm-convoy/">mammoth hailstorm pounded Calgary with damage in excess of $1 billion dollars</a>, the most expensive hailstorm in Canadian history. In early July, eastern Canada was subjected to both <a href="https://ottawa.ctvnews.ca/heat-wave-the-opening-act-for-a-hot-dry-summer-in-ottawa-environment-canada-1.4993033">persistent extreme heat coupled with high humidity</a> and <a href="https://toronto.ctvnews.ca/powerful-storm-leaves-west-end-toronto-homes-flooded-1.5018052">major flooding</a>.</p>
<p>As we cope with these events, questions invariably arise about what role climate change may have played. Has a particular extreme been made worse because of our changing climate? How will these extremes change in the future? </p>
<h2>Water cycle accelerating</h2>
<p>Many of these questions are linked with the hydrologic cycle — the evaporation of water from the Earth’s surface and its vegetation, the transport of water vapour in the atmosphere from one place to another and the ultimate return of the water to the surface as precipitation. </p>
<p>The water cycle speeds up when the climate warms. A warmer atmosphere holds more water vapour, creating the potential for more intense precipitation events. The evidence that human activity has warmed the global climate over the past century is incontrovertible. Satellite data available since 1988 indicate that the <a href="https://www.pnas.org/content/111/32/11636">atmosphere has moistened</a>, and that this is <a href="https://www.pnas.org/content/104/39/15248">primarily due to the human-induced warming of the climate</a>.</p>
<p>Individual extreme events are, however, influenced by many other factors. A storm can leave behind moisture at the surface that can re-evaporate and strengthen subsequent events. </p>
<p>The collision between a cold front and a lake breeze can lead to heavy precipitation. A delayed lake freeze-up during a warm winter can enhance lake-effect snowfall. Or a drought could limit local evapo-transpiration — evaporation from the land surface and transpiration from plants — eliminating the rainfall that comes from local moisture recycling and further intensifying hot, dry conditions.</p>
<h2>Heavy rainfall</h2>
<p>Many studies have examined precipitation-related change, <a href="https://changingclimate.ca/CCCR2019/">usually focusing on average conditions rather than extremes</a>. This is understandable because individual events, like a tornado or hail storm, are complex, and sparse ground observations and evolving techniques mean there aren’t yet long-term records that allow scientists to reliably estimate trends. </p>
<p>In contrast, numerous rainfall records beginning in the 1950s or earlier exist across the globe. Statistical analyses of data from these rain gauges confirm that rainfall extremes have grown more intense <a href="https://doi.org/10.1175/JCLI-D-12-00502.1">at the global</a> and <a href="https://www.pacificclimate.org/%7Efwzwiers/CONV/JCLI-D-19-0892_Accepted_2-Sept-2020.pdf">continental levels</a>, in agreement with <a href="https://link.springer.com/article/10.1007/s10584-013-0705-8">climate models</a>. </p>
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<img alt="A man stands in shin-deep water in an apartment." src="https://images.theconversation.com/files/355386/original/file-20200829-24-zxhqsi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/355386/original/file-20200829-24-zxhqsi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/355386/original/file-20200829-24-zxhqsi.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/355386/original/file-20200829-24-zxhqsi.JPG?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/355386/original/file-20200829-24-zxhqsi.JPG?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/355386/original/file-20200829-24-zxhqsi.JPG?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/355386/original/file-20200829-24-zxhqsi.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 man surveys the damage to his basement apartment after a severe thunderstorm caused localized flooding in Toronto on July 8, 2020.</span>
<span class="attribution"><span class="source">THE CANADIAN PRESS/Carlos Osorio</span></span>
</figcaption>
</figure>
<p>There are broad indications that these changes in rainfall extremes are due to human influence on the climate <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/grl.51010">at global</a> and <a href="https://www.pnas.org/content/117/24/13308">continental scales</a>. Extreme one-day rainfall events that occurred about once every 20 years in the past are <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/grl.51010">now occurring about once every 15 years</a>. </p>
<p>Even so, scientists still struggle to confidently say that a particular extreme rainfall event is the result of climate change. This is because there is naturally a large amount of variation in precipitation in one place, and the signal from climate change can get hidden within the natural noise. </p>
<h2>Future extremes</h2>
<p>Not all places have seen one-day rainfall extremes grow more intense over the past several decades, but that doesn’t mean it won’t happen in the future. The science indicates, with considerable confidence, that as the climate continues to warm, precipitation extremes will become substantially more intense in the <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1002/2018EF000813">mid-latitudes and northern land areas</a>, including Canada. </p>
<p><a href="https://hess.copernicus.org/articles/23/3437/2019/">Although details are uncertain, heavy snowfall, freezing rain and hail will all change with continued warming</a>.
For example, a recent study suggests that large hail <a href="https://www.nature.com/articles/nclimate3321">could become more likely in Alberta</a> by mid-century, but less likely in some other parts of Canada. </p>
<p>There is no doubt that human-induced greenhouse gas emissions have changed the climate. Nevertheless, the human imprint is often difficult to see in local meteorological observations. Despite that lack of direct “in your backyard” evidence, we should prepare for a future in which many precipitation-related extremes will become more intense.</p><img src="https://counter.theconversation.com/content/144535/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Francis Zwiers is the Director of the Pacific Climate Impacts Consortium, which is a not-for-profit federally incorporated climate services provider at the University of Victoria. He is also an Adjunct Professor in the Department of Mathematics and Statistics of the University of Victoria, and receives funding that supports his research from the Global Water Futures program, the Canadian Statistical Science Institute, the Natural Sciences and Engineering Research Council of Canada, and the Canadian Foundation for Innovation. </span></em></p><p class="fine-print"><em><span>Ronald Stewart is a professor in the Department of Environment and Geography at the University of Manitoba and receives funding from the Natural Sciences and Engineering Research Council of Canada and from Global Water Futures which is funded by the Canada First Research Excellence Fund.</span></em></p>Climate change has boosted the likelihood of heavy rainfall, hailstorms, flooding and drought seen in some parts of the world. What does the future hold?Francis Zwiers, Director, Pacific Climate Impacts Consortium, University of VictoriaRonald Stewart, Professor, Environment and Geography, University of ManitobaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1332192020-05-28T12:13:41Z2020-05-28T12:13:41ZWhat would it feel like to touch a cloud?<figure><img src="https://images.theconversation.com/files/336133/original/file-20200519-152298-1icmco7.jpg?ixlib=rb-1.1.0&rect=867%2C810%2C3877%2C2347&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">They may look comfy to sit on but you'd plummet through and hit the ground.</span> <span class="attribution"><a class="source" href="https://unsplash.com/photos/E9aetBe2w40">Sam Schooler/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span></figcaption></figure><figure class="align-left ">
<img alt="" src="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=293&fit=crop&dpr=1 600w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=293&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=293&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=368&fit=crop&dpr=1 754w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=368&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/281719/original/file-20190628-76743-26slbc.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=368&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px">
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<span class="caption"></span>
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<p><em><a href="https://theconversation.com/us/topics/curious-kids-us-74795">Curious Kids</a> is a series for children of all ages. If you have a question you’d like an expert to answer, send it to <a href="mailto:curiouskidsus@theconversation.com">curiouskidsus@theconversation.com</a>.</em></p>
<hr>
<blockquote>
<p><strong>What would it feel like to touch a cloud? – Violet V., age 6, Somerville, Massachusetts</strong></p>
</blockquote>
<hr>
<p>You might already know how it feels to touch a cloud without realizing it.</p>
<p>If you’ve ever been outside on a foggy day, you’ve essentially been inside a cloud, just one very close to the ground instead of high in the sky. Fog and clouds are both made of tiny water droplets – like the ones you can sometimes see or feel in a hot, steamy shower.</p>
<p>Clouds form through evaporation and condensation. Water in lakes, rivers, oceans or puddles evaporates into water vapor as the sun heats it up. <a href="https://sciencing.com/science-projects-teaching-evaporation-condensation-8029453.html">You can evaporate water yourself</a> by boiling it – watch it disappear as vapor.</p>
<figure>
<iframe width="440" height="260" src="https://www.youtube.com/embed/q87Ekar3emA?wmode=transparent&start=0" frameborder="0" allowfullscreen=""></iframe>
<figcaption><span class="caption">How do clouds form?</span></figcaption>
</figure>
<p>Water vapor, which is invisible, naturally rises up from the Earth’s surface into the atmosphere as warm bubbles, like the bubbles you’d see rising in a lava lamp. The higher it goes, the more it cools, until eventually the water vapor condenses back into liquid water.</p>
<p>Clouds are made of millions of these tiny liquid water droplets. The droplets scatter the colors of the sunlight equally, which makes <a href="https://www.metoffice.gov.uk/weather/learn-about/weather/types-of-weather/clouds/why-are-clouds-white">clouds appear white</a>. Even though they can look like cushy puffballs, a cloud can’t support your weight or hold anything up but itself.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/336200/original/file-20200519-152315-abcowj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/336200/original/file-20200519-152315-abcowj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/336200/original/file-20200519-152315-abcowj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=654&fit=crop&dpr=1 600w, https://images.theconversation.com/files/336200/original/file-20200519-152315-abcowj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=654&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/336200/original/file-20200519-152315-abcowj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=654&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/336200/original/file-20200519-152315-abcowj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=822&fit=crop&dpr=1 754w, https://images.theconversation.com/files/336200/original/file-20200519-152315-abcowj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=822&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/336200/original/file-20200519-152315-abcowj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=822&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Water vapor in your bathroom can fog up the mirror.</span>
</figcaption>
</figure>
<p>The process of evaporation and condensation in the atmosphere is similar to what happens in your bathroom when you take a hot shower: Warm water evaporates and then condenses back into water on the cold mirror.</p>
<p>Water vapor does not condense spontaneously. It needs tiny particles or a surface – like your bathroom mirror – on which to form a drop. <a href="https://scholar.google.com/citations?user=BSQl42wAAAAJ&hl=en&oi=ao">Atmospheric scientists like me</a> call these tiny particles cloud condensation nuclei, or CCN for short. These CCN are just dirt or dust particles that have been lifted by the wind and are <a href="https://gmao.gsfc.nasa.gov/research/aerosol/modeling/nr1_movie/">floating around in the atmosphere</a>.</p>
<p>Does that mean that places with a lot of dust and pollution, like cities, have more drops than clean places? Researchers have found more tiny droplets and more clouds in areas where there are a lot of these cloud condensation nuclei, while in areas without them fewer clouds are observed, <a href="https://eos.org/editors-vox/atmospheric-aerosol-in-the-changing-arctic">like over the ocean or the Arctic</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/336199/original/file-20200519-152288-wz4zrm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/336199/original/file-20200519-152288-wz4zrm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/336199/original/file-20200519-152288-wz4zrm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=336&fit=crop&dpr=1 600w, https://images.theconversation.com/files/336199/original/file-20200519-152288-wz4zrm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=336&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/336199/original/file-20200519-152288-wz4zrm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=336&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/336199/original/file-20200519-152288-wz4zrm.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=423&fit=crop&dpr=1 754w, https://images.theconversation.com/files/336199/original/file-20200519-152288-wz4zrm.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=423&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/336199/original/file-20200519-152288-wz4zrm.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=423&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Water evaporates and rises up into the sky, condensing to form clouds.</span>
<span class="attribution"><a class="source" href="https://svs.gsfc.nasa.gov/30580">NASA</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>As cloud droplets rise in the atmosphere, the air temperature decreases. The tiny cloud droplets start to freeze when the temperature drops below below 32 degrees Fahrenheit (0 degrees Celsius). It’s the exact same process as making ice cubes in a freezer.</p>
<p>The frozen droplets are now ice crystals. They continue to grow in size as water vapor turns into ice and sticks onto them. Scientists call this process of a gas turning into a solid “deposition.” It creates the beautiful branched ice crystals that you find in snowstorms.</p>
<p>Steady updrafts of air keep these very light water droplets or ice crystals floating in the cloud. So how do they turn into rain and snow and fall to the ground? Easy, they join forces.</p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/336201/original/file-20200519-152344-1qvj0ie.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/336201/original/file-20200519-152344-1qvj0ie.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/336201/original/file-20200519-152344-1qvj0ie.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=715&fit=crop&dpr=1 600w, https://images.theconversation.com/files/336201/original/file-20200519-152344-1qvj0ie.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=715&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/336201/original/file-20200519-152344-1qvj0ie.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=715&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/336201/original/file-20200519-152344-1qvj0ie.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=899&fit=crop&dpr=1 754w, https://images.theconversation.com/files/336201/original/file-20200519-152344-1qvj0ie.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=899&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/336201/original/file-20200519-152344-1qvj0ie.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=899&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Those spiky arms can grab on to other snowflakes.</span>
<span class="attribution"><a class="source" href="https://unsplash.com/photos/5p_hbvdcEvo">Aaron Burden/Unsplash</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Larger droplets collect smaller droplets on their way to the ground as raindrops. Snow grows in a similar way, with the crystals sticking to each other. Their little arms can interlock to form a bigger snowflake. When water droplets merge with ice crystals, that makes hail.</p>
<p>Rain droplets grow on their way down to the ground, eventually becoming unstable and breaking up. <a href="https://www.washington.edu/news/2004/07/22/record-rain-uw-scientists-find-some-of-the-biggest-raindrops-ever/">The largest raindrop</a> that researchers have found was about a third of an inch across. Some <a href="https://www.nytimes.com/2007/03/20/science/20snow.html">giant snowflakes</a> have been reported to be as big as 6 inches across. And the biggest piece of hail? In 2010, someone found <a href="https://www.weather.gov/abr/vivianhailstone">a hailstone 8 inches in diameter</a> in South Dakota and took a photo – so scientists know it was real.</p>
<p>That would be a lot more painful to collide with than a wispy cloud of water vapor.</p>
<hr>
<p><em>Hello, curious kids! Do you have a question you’d like an expert to answer? Ask an adult to send your question to <a href="mailto:curiouskidsus@theconversation.com">CuriousKidsUS@theconversation.com</a>. Please tell us your name, age and the city where you live.</em></p>
<p><em>And since curiosity has no age limit – adults, let us know what you’re wondering, too. We won’t be able to answer every question, but we will do our best.</em></p><img src="https://counter.theconversation.com/content/133219/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Katja Friedrich 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>You might have already felt what it would be like inside a cloud made of condensed water vapor.Katja Friedrich, Associate Professor of Atmospheric and Oceanic Sciences, University of Colorado BoulderLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/1028792018-09-20T10:37:31Z2018-09-20T10:37:31ZDestructive 2018 hail season a sign of things to come<figure><img src="https://images.theconversation.com/files/237201/original/file-20180919-143281-xzckd3.jpg?ixlib=rb-1.1.0&rect=0%2C38%2C4920%2C3251&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Icy hailstones can do major damage, depending where they land.</span> <span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Severe-Weather-Nebraska/1e8e19915cb142f28ee3a7c111ab3d5d/1/0">AP Photo/Nati Harnik</a></span></figcaption></figure><p>As ominous skies moved overhead just after noon on Aug. 6, the <a href="https://www.denverpost.com/2018/08/07/cheyenne-mountain-zoo-hail-storm/">small splash of a hailstone</a> was heard in the pool of the bear exhibit at the Cheyenne Mountain Zoo in Colorado Springs. Moments later, a barrage of ice baseballs began falling from the sky, with one or two softball-sized hailstones in the mix. People and animals scrambled for cover.</p>
<p><div data-react-class="Tweet" data-react-props="{"tweetId":"1026678308761755648"}"></div></p>
<p>In the aftermath, the <a href="https://kdvr.com/2018/08/10/cheyenne-mountain-zoo-to-reopen-after-hail-damages-buildings-kills-several-animals/">hail storm’s wrath was revealed</a>: at least eight people injured, five animals killed and hundreds of cars severely damaged in the zoo parking lot.</p>
<p>Whether you’re a farmer managing hundreds of acres of corn, a school teacher in care of young children at recess, or an unsuspecting tourist excited to watch the dolphin show, hail storms matter. This summer’s Colorado Springs event is yet another reminder of the destruction that large hail can bring. These large hail events seem to be more and more common, which has prompted <a href="https://scholar.google.com/citations?user=mW88UtIAAAAJ&hl=en">atmospheric scientists like me</a> to investigate trends in hail storms, as well as other severe weather phenomena. A better scientific understanding of hail storms can help increase public awareness, including of how best to protect one’s life and property.</p>
<h2>A record-setting year</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/237159/original/file-20180919-158240-1ih9r4f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/237159/original/file-20180919-158240-1ih9r4f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/237159/original/file-20180919-158240-1ih9r4f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=599&fit=crop&dpr=1 600w, https://images.theconversation.com/files/237159/original/file-20180919-158240-1ih9r4f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=599&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/237159/original/file-20180919-158240-1ih9r4f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=599&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/237159/original/file-20180919-158240-1ih9r4f.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=753&fit=crop&dpr=1 754w, https://images.theconversation.com/files/237159/original/file-20180919-158240-1ih9r4f.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=753&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/237159/original/file-20180919-158240-1ih9r4f.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=753&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 more times a hailstone cycles through a cloud, the larger it can grow before falling out.</span>
<span class="attribution"><a class="source" href="https://scijinks.gov/rain/">SciJinks</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
</figcaption>
</figure>
<p>Hail is precipitation that <a href="https://www.wunderground.com/prepare/hail">falls in the form of ice</a>. In basic terms, hailstones form as water is lofted into the upper cold regions of a thunderstorm, where it freezes. Supercooled liquid water at these heights can continue to add mass to a small hailstone – eventually it becomes too heavy and falls out of the cloud.</p>
<p>The largest hailstones are found in strong thunderstorms, <a href="https://www.weather.gov/ama/supercell">called supercells</a>, which have sufficiently strong updrafts to allow hailstones to reach the ice region of the cloud, thus <a href="https://www.nssl.noaa.gov/education/svrwx101/hail/forecasting/">acquiring more mass before falling out</a>. Supercells, and thus large hail, are aided by warm and moist conditions that promote strong, juicy updrafts and also a wind field that strengthens and turns with height.</p>
<p>For anyone living in the Great Plains, this year has been a hail season to remember, with many more large hailstones being reported than usual. Neither the total number of severe hail reports – defined by the National Weather Service’s <a href="https://www.spc.noaa.gov">Storm Prediction Center</a> (SPC) as hail in excess of 1 inch in diameter – nor the number of days in which severe hail has fallen, were out of the ordinary. But in 2018, the percentage of hail greater than 2 inches in diameter certainly was.</p>
<p>Here in Colorado, over 20 percent of severe hail reports through the beginning of September have been at least 2 inches. Three percent have been at least 3 inches – bigger than a standard 2.75-inch baseball. These are the highest such percentages in state history. Moreover, Colorado saw a new record, with hail greater than 3 inches in diameter reported 10 times, over seven different days.</p>
<p><iframe id="fxaBU" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/fxaBU/2/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>And these trends hold nationally, too, according to <a href="https://www.spc.noaa.gov/wcm/">preliminary SPC reports</a>. Across the country, percentages of large hailstones are among the highest seen since the turn of this century. Geographically, very large hail reports for 2018 stretch from Idaho to Florida to Connecticut, with a maximum in the western Great Plains.</p>
<p><iframe id="63AWu" class="tc-infographic-datawrapper" src="https://datawrapper.dwcdn.net/63AWu/3/" height="400px" width="100%" style="border: none" frameborder="0"></iframe></p>
<p>So what’s going on?</p>
<h2>A new normal?</h2>
<p>Having an increasingly higher proportion of large hail is not an encouraging trend for home or automobile owners.</p>
<p>The <a href="https://www.spc.noaa.gov/wcm/">SPC hail database</a> is the country’s primary source of hail reports. They come from a variety of sources including trained spotters, meteorologists, law enforcement and the general public. As such, the database has <a href="http://www.ejssm.org/ojs/index.php/ejssm/article/view/149/104">some inherent reporting biases</a>. For example, reports tend to cluster around places where people live. And people tend to report hail of sizes they associate with common objects, such as golf balls or baseballs.</p>
<p>But it’s hard to believe people are suddenly becoming more excited to report only large hail, while ignoring the quarter-sized hail that can still be a nuisance. In fact, this year may be a hint of what will become commonplace in the future.</p>
<p>Effectively simulating the growth of hail in a model is nearly impossible due to the intricate microphysical processes involved. Imagine the difficulty of trying to account for hail’s erratic wobbling and tumbling within a cloud and the constant addition and loss of water on its surface. As icing on the cake, each hailstone has a unique shape, and it’s hardly ever spherical. Nevertheless, it is possible to look at changes in variables that are important for hail growth.</p>
<p>Recent research assessed the <a href="https://doi.org/10.1038/nclimate3321">effects of climate change on hail size and frequency</a> using a hail growth model with environmental variables adjusted for climate change. The relatively cool and dry Plains region is expected to become warmer and more moist in a future climate, leading to stronger updrafts and more moisture availability. Under these conditions, scientists found that both average hail diameter and frequency of large hail occurrence are expected to increase across the central part of the country.</p>
<p>Researchers at the National Center for Atmospheric Research have found that in a future climate, there will be <a href="https://doi.org/10.1007/s00382-017-4000-7">more strong thunderstorms and fewer weak ones</a>. This result again favors an increase in larger hailstone sizes, since stronger thunderstorms allow the hail to be cycled through the cloud layer for a longer time.</p>
<h2>Untangling what drives the trend</h2>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/237200/original/file-20180919-158240-5x19vd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/237200/original/file-20180919-158240-5x19vd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/237200/original/file-20180919-158240-5x19vd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=800&fit=crop&dpr=1 600w, https://images.theconversation.com/files/237200/original/file-20180919-158240-5x19vd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=800&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/237200/original/file-20180919-158240-5x19vd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=800&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/237200/original/file-20180919-158240-5x19vd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=1005&fit=crop&dpr=1 754w, https://images.theconversation.com/files/237200/original/file-20180919-158240-5x19vd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=1005&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/237200/original/file-20180919-158240-5x19vd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=1005&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Hard, dense hailstones can do some serious damage.</span>
<span class="attribution"><a class="source" href="http://www.apimages.com/metadata/Index/Severe-Weather-Plains/b7de798aa0d240e4ae4e712b240ff500/2/0">Stacey Valdez via AP</a></span>
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<p>Is a changing climate all that’s responsible for what appears to be a shift toward storms with greater hailstone sizes that occur more frequently? What about population dynamics and urbanization? After all, hailstones can only be reported where people are around to measure them.</p>
<p>These questions have prompted my current research that aims to differentiate the relative contributions from climate change and population change to future hail storm risk. I’m combining a weather model that projects future changes in variables that promote hail storms with spatial population projections from NCAR and the EPA. The goal is to assess where and how much the greatest human risk from large hail is expected to be in the future.</p>
<p>Compared to tornadoes and hurricanes, large hail has received relatively little research attention, but that’s starting to change: A <a href="https://www.mmm.ucar.edu/north-american-hail-workshop">major international workshop</a> was held in August 2018 to share research ideas and results. Achieving better understanding of how hail storms might look in the future, and which places might become more at risk, is of great worth for decision-makers, the insurance industry and the general public. Hopefully, such knowledge will spare everyone – including vacationing families at a popular zoo – the nightmare of dealing with destruction by softball-sized hail.</p><img src="https://counter.theconversation.com/content/102879/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Samuel Childs receives funding from National Science Foundation Grants DGE-1321845 and AGS-1637244. His PhD advisor is Dr. Russ Schumacher.</span></em></p>The future climate that scientists predict for the middle of the United States is one that will foster more hail events with bigger hailstones.Samuel Childs, PhD Student in Atmospheric Science, Colorado State UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/868562017-11-28T03:44:47Z2017-11-28T03:44:47ZAll hail new weather radar technology, which can spot hailstones lurking in thunderstorms<p>An Australian spring wouldn’t be complete without thunderstorms and a visit to the Australian Bureau of Meteorology’s weather radar website. But a new type of radar technology is aiming to make weather radar even more useful, by helping to identify those storms that are packing hailstones.</p>
<p>Most storms just bring rain, lightning and thunder. But others can produce hazards including destructive flash flooding, winds, large hail, and even the occasional tornado. For these potentially dangerous storms, the Bureau issues <a href="http://www.bom.gov.au/weather-services/severe-weather-knowledge-centre/WarningsInformation_SW_STSW.shtml">severe thunderstorm warnings</a>. </p>
<p>For metropolitan regions, warnings identify severe storm cells and their likely path and hazards. They provide a predictive “nowcast”, such as forecasts up to three hours before impact for suburbs that are in harm’s way.</p>
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<em>
<strong>
Read more:
<a href="https://theconversation.com/to-understand-how-storms-batter-australia-we-need-a-fresh-deluge-of-data-68487">To understand how storms batter Australia, we need a fresh deluge of data</a>
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<p>When monitoring thunderstorms, weather radar is the primary tool for forecasters. Weather radar scans the atmosphere at multiple levels, <a href="https://www.youtube.com/watch?v=Yrq2TVdM8HI">building a 3D picture of thunderstorms</a>, with a 2D version shown on the bureau’s website. </p>
<p>This is particularly important for hail, which forms several kilometres above ground in towering storms where temperatures are well below freezing.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/195404/original/file-20171120-18561-y4ju21.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/195404/original/file-20171120-18561-y4ju21.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/195404/original/file-20171120-18561-y4ju21.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=644&fit=crop&dpr=1 600w, https://images.theconversation.com/files/195404/original/file-20171120-18561-y4ju21.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=644&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/195404/original/file-20171120-18561-y4ju21.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=644&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/195404/original/file-20171120-18561-y4ju21.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=809&fit=crop&dpr=1 754w, https://images.theconversation.com/files/195404/original/file-20171120-18561-y4ju21.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=809&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/195404/original/file-20171120-18561-y4ju21.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=809&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">Bureau of Meteorology 60-minute nowcast showing location and projected track of severe thunderstorms in 10-minute steps.</span>
<span class="attribution"><span class="source">Australian Bureau of Meteorology</span></span>
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<p>In terms of insured losses, hailstorms have caused more insured losses than any other type of severe weather events in Australia. Brisbane’s November 2014 hailstorms cost an estimated <a href="http://www.icadataglobe.com/access-catastrophe-data">A$1.41 billion</a>, while Sydney’s April 1999 hailstorm, at <a href="http://www.icadataglobe.com/access-catastrophe-data">A$4.3 billion</a>, remains the nation’s most costly natural disaster. </p>
<h1>Breaking the ice</h1>
<p>Nonetheless, accurately detecting and estimating hail size from weather radar remains a challenge for scientists. This challenge stems from the diversity of hail. Hailstones can be large or small, densely or sparsely distributed, mixed with rain, or any combination of the above.</p>
<p>Conventional radars measure the scattering of the radar beams as they pass through precipitation. However, a few large hailstones can look the same as lots of small ones, making it hard to determine hailstones’ size.</p>
<p>A new type of radar technology called “dual-polarisation” or “dual-pol” can solve this problem. Rather than using a single radar beam, dual-pol uses two simultaneous beams aligned horizontally and vertically. When these beams scatter off precipitation, they provide relative measures of horizontal and vertical size.</p>
<p>Therefore, an observer can see the difference between flatter shapes of rain droplets and the rounder shapes of hailstones. Dual-pol can also more accurately measure the size and density of rain droplets, and whether it’s a mixture or just rain. </p>
<p>Together, these capabilities mean that dual-pol is a game-changer for hail detection, size estimation and nowcasting.</p>
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<h1>Into the eye of the storm</h1>
<p>Dual-pol information is <a href="http://media.bom.gov.au/releases/380/mount-stapylton-radar-switched-on-and-ready-for-storm-season/">now streaming</a> from the recently upgraded operational radars in Adelaide, Melbourne, Sydney and Brisbane. It allows forecasters to detect hail earlier and with more confidence. </p>
<p>However, more work is needed to accurately estimate hail size using dual-pol. The ideal place for such research is undoubtedly southeast Queensland, the hail capital of the east coast.</p>
<p>When it comes to thunderstorm hazards, nothing is closer to reality than scientific observations from within the storm. In the past, this approach was considered too costly, risky and demanding. Instead, researchers resorted to models or historical reports. </p>
<p>The <a href="http://uqaorg.com">Atmospheric Observations Research Group</a> at the University of Queensland (UQ) has developed a unique capacity in Australia to deploy mobile weather instrumentation for severe weather research. In partnership with the UQ <a href="http://www.civil.uq.edu.au/wirl">Wind Research Laboratory</a>, Guy Carpenter and staff in the Bureau of Meteorology’s Brisbane office, the Storms Hazards Testbed has been established to advance the nowcasting of hail and wind hazards.</p>
<p>Over the next two to three years, the testbed will take a mobile weather radar, meteorological balloons, wind measurement towers and hail size sensors into and around <a href="https://youtu.be/4gMLUQuAR2M">severe thunderstorms</a>. Data from these instruments provide high-resolution case studies and ground-truth verification data for hazards observed by the Bureau’s dual-pol radar.</p>
<p>Since the start of October, we have intercepted and sampled five hailstorms. If you see a convoy of UQ vehicles heading for ominous dark clouds, head in the opposite direction and follow us on <a href="https://facebook.com/uqhail">Facebook</a> instead.</p>
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<img alt="" src="https://images.theconversation.com/files/195410/original/file-20171120-18533-1f1v9aj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/195410/original/file-20171120-18533-1f1v9aj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=450&fit=crop&dpr=1 600w, https://images.theconversation.com/files/195410/original/file-20171120-18533-1f1v9aj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=450&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/195410/original/file-20171120-18533-1f1v9aj.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=450&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/195410/original/file-20171120-18533-1f1v9aj.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=566&fit=crop&dpr=1 754w, https://images.theconversation.com/files/195410/original/file-20171120-18533-1f1v9aj.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=566&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/195410/original/file-20171120-18533-1f1v9aj.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">
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<span class="caption">UQ mobile radar deployed for thunderstorm monitoring.</span>
<span class="attribution"><span class="source">Kathryn Turner</span></span>
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<p>Unfortunately, the UQ storm-chasing team can’t get to every severe thunderstorm, so we need your help! The project needs citizen scientists in southeast Queensland to report hail through #UQhail. Keep a ruler or object for scale (coins are great) handy and, when a hailstorm has safely passed, measure the largest hailstone. </p>
<p>Submit reports via <a href="http://uqhail.com">uqhail.com</a>, <a href="mailto:uqhail@outlook.com">email</a>, <a href="https://facebook.com/uqhail">Facebook</a> or <a href="https://twitter.com/uq_hail">Twitter</a>. We greatly appreciate photos with a ruler or reference object and approximate location of the hail.</p>
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<a href="https://images.theconversation.com/files/195405/original/file-20171120-18555-14b7aw4.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/195405/original/file-20171120-18555-14b7aw4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/195405/original/file-20171120-18555-14b7aw4.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=515&fit=crop&dpr=1 600w, https://images.theconversation.com/files/195405/original/file-20171120-18555-14b7aw4.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=515&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/195405/original/file-20171120-18555-14b7aw4.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=515&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/195405/original/file-20171120-18555-14b7aw4.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=647&fit=crop&dpr=1 754w, https://images.theconversation.com/files/195405/original/file-20171120-18555-14b7aw4.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=647&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/195405/original/file-20171120-18555-14b7aw4.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=647&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
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<span class="caption">How to report for uqhail.</span>
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<p>Combining measurements, hail reports and the Bureau of Meteorology’s dual-pol weather radar data, we are working towards developing algorithms that will allow hail to be forecast more accurately. This will provide greater confidence in warnings and those vital extra few minutes when cars can be moved out of harm’s way, reducing the impact of storms.</p>
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<strong>
Read more:
<a href="https://theconversation.com/tropical-thunderstorms-are-set-to-grow-stronger-as-the-world-warms-85745">Tropical thunderstorms are set to grow stronger as the world warms</a>
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<p>Advanced techniques developed from storm-chasing and citizen science data will be applied across the Australian dual-pol radar network in Sydney, Melbourne and Adelaide. </p>
<p>Who knows, in the future if the Bureau’s weather radar shows a thunderstorm heading your way, your reports might even have helped to develop that forecast.</p><img src="https://counter.theconversation.com/content/86856/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Joshua Soderholm receives funding from Guy Carpenter, Fugro Roames and the National Environmental Science Program. </span></em></p><p class="fine-print"><em><span>Matthew Mason receives funding from the Australian Research Council. </span></em></p><p class="fine-print"><em><span>Alain Protat, Hamish McGowan, and Harald Richter 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>New “dual-pol” weather radars promise to spot large hailstones forming inside thunderstorms, giving people a heads-up when it’s about to hail.Joshua Soderholm, Research scientist, The University of QueenslandAlain Protat, Principal Research Scientist, Australian Bureau of MeteorologyHamish McGowan, Professor, The University of QueenslandHarald Richter, Senior Research Scientist, Australian Bureau of MeteorologyMatthew Mason, Lecturer in Civil Engineering, The University of QueenslandLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/684872016-11-14T03:20:42Z2016-11-14T03:20:42ZTo understand how storms batter Australia, we need a fresh deluge of data<p><em>The journal <a href="http://link.springer.com/journal/10584">Climatic Change</a> has published a <a href="http://link.springer.com/journal/10584/139/1/page/1">special edition</a> of review papers discussing major natural hazards in Australia. This article is one of a <a href="https://theconversation.com/au/topics/australian-natural-hazards-series-32987">series</a> looking at those threats in detail.</em></p>
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<p>Storms, wind and hail do a lot of damage to Australians and their property. The <a href="http://www.bom.gov.au/nsw/sevwx/14april1999.shtml">1999 Sydney hailstorm</a>, for instance, cost <a href="http://forms2.rms.com/rs/729-DJX-565/images/scs_1999_sydney_hailstorm.pdf">A$1.7 billion</a> in insured losses. That makes it the biggest single insurance loss in Australian history; in today’s money it would have cost more than A$4 billion.</p>
<p>More recently, one of the most severe storms in decades caused a <a href="http://www.abc.net.au/news/2016-09-28/sa-weather-south-australia-without-power-as-storm-hits/7885930">statewide blackout</a> in South Australia in September. The intense low-pressure system featured <a href="https://www.theguardian.com/australia-news/2016/nov/14/south-australian-blackout-included-seven-tornadoes-bureau-of-meteorology-says">seven tornadoes</a> that tore down three major transmission lines.</p>
<p>Our understanding of wind and hail depends on the type of storm that generates them – and this is where it gets complicated. Thunderstorms can generate not just heavy rainfall but also high winds, lightning and hail, albeit in very localised areas. Large-scale storms such as tropical cyclones are a different phenomenon altogether, bringing not just destructive winds, but also storm surges and soaking rains, often over wide areas. </p>
<p>This complexity makes storms difficult to study, because limited research resources are spread across the many different storm types and their associated hazards.</p>
<p>To help address these issues, we <a href="http://link.springer.com/article/10.1007/s10584-016-1737-7">collated and reviewed</a> the latest knowledge and understanding of storms in Australia, covering the current scientific literature on the assessment, causes, observed trends and future projected changes of storm hazards, with a specific focus on severe wind and hail. We found that progress has been made in many areas, but also that much remains to be done.</p>
<h2>Are we getting more or less storms?</h2>
<p>In short - we don’t know with confidence. Despite the severity of the impacts wrought by storms, there is limited observational data for some types of storms and their associated hazards, particularly for the estimation of hail and wind. </p>
<p>Current estimates of the hail hazard in Australia, for example, are available only from the Bureau of Meteorology’s <a href="http://www.bom.gov.au/australia/stormarchive/">severe storm archive</a>, which suffers from large uncertainties associated with biases and changing reporting practices. This makes it unsuitable for assessing the climatology of hail storms on a national scale. </p>
<p>Similarly, issues such as changes to Automatic Weather Stations (AWS) and limited records of atmospheric pressure observations, have hampered efforts to develop <a href="http://www.bom.gov.au/climate/data-services/amoj_wind_2010.pdf">high-quality surface wind datasets</a> across Australia. Bob Dylan might have been right when he told us “<a href="http://bobdylan.com/songs/subterranean-homesick-blues/">you don’t need a weatherman to know which way the wind blows</a>,” but then again he didn’t win his Nobel Prize for meteorology.</p>
<p>European researchers have <a href="https://www.hindawi.com/journals/tswj/2013/494971/">analysed hailstorm trends</a> using networks of devices called “<a href="http://www.sciencedirect.com/science/article/pii/S0169809508002536">hailpads</a>”. But these records do not exist in Australia, and so there is a significant gap in our knowledge about hailstorm histories and trends.</p>
<p>The projections of future wind hazard in and around Australia are equally limited and differ from region to region. For example, in the tropics, research suggests that <a href="http://www.nature.com/nature/journal/v509/n7500/full/nature13278.html">extreme wind hazard may decrease in the future</a>, although confidence in this prediction is low. Meanwhile, <a href="http://www.geosci-model-dev.net/7/621/2014/gmd-7-621-2014.html">summer wind increases</a> are possible in those parts of Australia that are subjected to <a href="http://www.bom.gov.au/nsw/sevwx/facts/ecl.shtml">East Coast Lows</a>. </p>
<p>We also don’t really know what to expect from <a href="http://www.sciencedirect.com/science/article/pii/S0169809512000968">future severe thunderstorms</a>, and while <a href="http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00426.1?mobileUi=0&journalCode=clim">research suggests</a> that they may become more frequent in southeastern Australia, there is a wide range of uncertainty around this projection.</p>
<p>For future trends in hail, again there are only a few studies currently available, but there is at least an indication of <a href="https://blogs.csiro.au/climate-response/stories/four-degrees-of-global-warming-australia-in-a-hot-world/">increases in hail frequency</a> in southeastern regions.</p>
<p>But while the picture is very uncertain for now, we hope this uncertainty will be reduced with the help of improvements in both the observation and computational modelling of storms and their associated hazards. We are growing more confident in our <a href="http://onlinelibrary.wiley.com/doi/10.1002/wcc.371/references;jsessionid=A69988FD600B9BA5E9C478AD7DF99322.f01t01?globalMessage=0">predictions for tropical cyclone</a>, forecasting that the overall number will decline, but that the strongest storms will grow stronger still.</p>
<p>We also hope to improve our understanding of severe thunderstorms by using remote sensing platforms to record hail and extreme wind events right across Australia. These include the <a href="http://www.gpats.com.au">GPATS lightning-detection network</a>, the new <a href="http://ds.data.jma.go.jp/mscweb/data/himawari/sat_img.php?area=fd_">Himawari-8 and 9 satellites</a>, and the Bureau of Meteorology’s <a href="http://www.cawcr.gov.au/technical-reports/CTR_055.pdf">soon-to-be upgraded radar network</a>. Validation of these techniques, of course, will also require high-quality direct observations of these severe weather conditions – the very thing we currently lack.</p>
<h2>Is this where you come in?</h2>
<p>Citizen scientists may, however, help to fill some of these gaps. There are exciting prospects for improving severe weather observations, such as the success of the <a href="http://mping.nssl.noaa.gov/">mPING</a> crowdsourced weather reports project in the United States, which allows participants to use a mobile phone app to report severe weather, which then feeds into <a href="http://journals.ametsoc.org/doi/abs/10.1175/BAMS-D-13-00014.1">new research</a>. </p>
<p>This approach could prove to be an excellent way of getting data in such a vast and diverse landscape as Australia, while simultaneously engaging with both the public and the atmospheric science community. We could also enlist the help of <a href="http://www.turing-gateway.cam.ac.uk/mfsg_sep2015">scientific study groups</a>, which bring together academics, scientists and industry partners to exchange ideas and develop research techniques.</p>
<p>“<a href="http://www.william-shakespeare.info/act5-script-text-julius-caesar.htm">The storm is up, and all is on the hazard</a>,” cried Cassius in William Shakespeare’s <em>Julius Caesar</em>. How true that is of storms in Australia. </p>
<p>If we don’t increase our observational and research abilities, we might never fully understand the impacts of severe storms, much less be able to deal with them.</p><img src="https://counter.theconversation.com/content/68487/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Chris White receives funding from various Tasmanian State Government research funding programs, Wine Australia and the Bushfire and Natural Hazard CRC.</span></em></p><p class="fine-print"><em><span>Jason Evans receives funding from the Australian Research Council, the National Environmental Science Programme Earth Systems and Climate Change Hub, Sydney Water, Water Research Australia, and various NSW state government research funding programs.</span></em></p><p class="fine-print"><em><span>Kevin Walsh receives funding from the Australian Research Council and other international funding organizations.</span></em></p>Severe storms bring a complex mixture of weather conditions, often in a very localised area. This unpredictability can make them very damaging, and very hard to study too.Christopher J White, Lecturer in Environmental Engineering, University of TasmaniaJason Evans, Associate Professor, UNSW SydneyKevin Walsh, Reader, School of Earth Sciences, The University of MelbourneLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/353272014-12-18T19:46:39Z2014-12-18T19:46:39ZAustralia faces a stormier future thanks to climate change<figure><img src="https://images.theconversation.com/files/67450/original/image-20141217-19707-1k6g87x.jpeg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">'Plates of the Outback' - A supercell thunderstorm near Urana, NSW drifts over the landscape.</span> <span class="attribution"><span class="source">John Allen</span>, <span class="license">Author provided</span></span></figcaption></figure><p>The <a href="http://www.abc.net.au/news/2014-12-04/brisbanites-still-cleaning-up-after-last-weeks-mega-storm/5944768">supercell</a> that hit Brisbane on November 27 this year caused more than A$500 million worth of damage, produced hail up to 7.5 cm in diameter, and lashed the city with winds of more than 140 km an hour. </p>
<p>In the news, we hear about tornadoes or supercells, and wonder if climate change is beginning to have an impact on these events. </p>
<p>In fact, the evidence suggests that while there has been no increase in severe storm activity in the past, we are likely to see stronger and more frequent storms in the future.</p>
<h2>The science of storms</h2>
<p>Growing up in Sydney’s western suburbs, I remember the summer thunderstorms appearing in the afternoon to the west, and wondering just why we see these castles in the sky. </p>
<p>Thunderstorms form when moisture and warmth near the Earth’s surface is overlapped by cooler air, causing an “updraft” of rising air. The more warm and moist the air, the stronger the <a href="http://en.wikipedia.org/wiki/Atmospheric_instability">thunderstorm’s updraft</a>. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/67448/original/image-20141217-19873-18m13c8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/67448/original/image-20141217-19873-18m13c8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/67448/original/image-20141217-19873-18m13c8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=383&fit=crop&dpr=1 600w, https://images.theconversation.com/files/67448/original/image-20141217-19873-18m13c8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=383&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/67448/original/image-20141217-19873-18m13c8.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=383&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/67448/original/image-20141217-19873-18m13c8.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=482&fit=crop&dpr=1 754w, https://images.theconversation.com/files/67448/original/image-20141217-19873-18m13c8.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=482&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/67448/original/image-20141217-19873-18m13c8.jpg?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">An example of a supercell thunderstorm updraft near Chingapook, Victoria. The red lines show where warm moist air moves towards the storm, and rises through the cooler dry air roughly outlined by the blue line. Wind shear pushes the precipitation away from the updraft, and allows the storm to rotate clockwise, producing a supercell.</span>
<span class="attribution"><span class="source">John Allen</span></span>
</figcaption>
</figure>
<p>Thunderstorm clouds are like the bubbles you see in a saucepan of water on the stove, where the heated water rises through cooler water above. Most of the time, a thunderstorm fills the sky for an hour, rises, rains and then disappears as if it was never there. </p>
<figure class="align-right zoomable">
<a href="https://images.theconversation.com/files/67275/original/image-20141215-5257-hn02sd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/67275/original/image-20141215-5257-hn02sd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=237&fit=clip" srcset="https://images.theconversation.com/files/67275/original/image-20141215-5257-hn02sd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=468&fit=crop&dpr=1 600w, https://images.theconversation.com/files/67275/original/image-20141215-5257-hn02sd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=468&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/67275/original/image-20141215-5257-hn02sd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=468&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/67275/original/image-20141215-5257-hn02sd.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=589&fit=crop&dpr=1 754w, https://images.theconversation.com/files/67275/original/image-20141215-5257-hn02sd.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=589&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/67275/original/image-20141215-5257-hn02sd.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=589&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Locations with reported severe thunderstorms for Australia for the period 2003-2010. 1550 events represent observations of tornadoes (red), hail (blue) and wind (green).</span>
<span class="attribution"><span class="source">John Allen</span></span>
</figcaption>
</figure>
<p>But in certain situations, these storms can become “severe”, <a href="http://www.bom.gov.au/vic/sevwx/about.shtml">producing hail in excess of 2 cm, wind gusts above 90 km per hour and sometimes tornadoes</a>. To form, severe thunderstorms typically need some degree of changing wind speed and direction at different levels of the atmosphere — known as wind shear. </p>
<p>If you’ve ever looked up at the sky and seen clouds moving in different directions, that is wind shear. Wind shear organises thunderstorms, moving rain away from the updraft, and allowing the storm to grow outside the normal lifetime of a thunderstorm, becoming stronger. The strongest of these organised storms are known as supercells and produce most hail larger than 5 cm, as well as tornadoes.</p>
<h2>Severe storms widespread in Australia</h2>
<p>Every year, Australia sees many severe thunderstorms, but we only hear about the few that hit populated areas, as someone needs to be present to observe the effects of a storm. </p>
<p>In reality, severe thunderstorms are found over the entire continent, but the intersection between tropical moisture and stronger wind shear means that they are most commonly found over the east coast and interior, stretching from Rockhampton to Melbourne. </p>
<p>To estimate their frequency, we can use a combination of potential updraft strength and wind shear to give an idea of how many days conditions are right for severe thunderstorm development. Using this approach, we can estimate Brisbane gets around 25 favourable days, Sydney 20 and Melbourne 10 days per year.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/67348/original/image-20141216-14157-t7fevu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/67348/original/image-20141216-14157-t7fevu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/67348/original/image-20141216-14157-t7fevu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=309&fit=crop&dpr=1 600w, https://images.theconversation.com/files/67348/original/image-20141216-14157-t7fevu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=309&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/67348/original/image-20141216-14157-t7fevu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=309&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/67348/original/image-20141216-14157-t7fevu.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=388&fit=crop&dpr=1 754w, https://images.theconversation.com/files/67348/original/image-20141216-14157-t7fevu.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=388&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/67348/original/image-20141216-14157-t7fevu.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=388&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">‘In Need of Rescue’ - A squall line moves along the Queensland coast toward Nowra.</span>
<span class="attribution"><span class="source">John Allen</span></span>
</figcaption>
</figure>
<h2>Has 2014 been particularly stormy?</h2>
<p>Overall, the frequency of severe storms in 2014 was about average, or even slightly below. Perhaps we are just forgetting some of those days when the storms weren’t as extreme, or those which missed populated areas. </p>
<p>The Brisbane supercell hailstorm of November 27 has a damage bill rising above <a href="http://www.abc.net.au/news/2014-12-04/brisbanites-still-cleaning-up-after-last-weeks-mega-storm/5944768">A$500 million</a>, but is far from unprecedented in either hail size or damage (<a href="http://hardenup.org/umbraco/customContent/media/600_Brisbane_SevereStorm_1985.pdf">in 1985 a similar event caused A$1.7 billion in equivalent damage</a>). </p>
<p>Similar hail events have often befallen Melbourne (<a href="http://www.theage.com.au/victoria/storm-brings-chaos-to-melbourne-20100306-ppm4.html">2010</a>, <a href="http://www.abc.net.au/news/2011-12-26/christmas-day-hail-storm-hits-melbourne/3747854">2011</a>), Perth (<a href="http://www.abc.net.au/news/2010-03-22/perth-reeling-from-freak-storm/375436">2010</a>), and Sydney (<a href="http://www.bom.gov.au/nsw/sevwx/0708summ.shtml">2007</a>). </p>
<p>In terms of damaging winds, estimated gusts (around 140 km per hour) were not as strong as the 1985 storm (around 185 km per hour), but similar to the storm that affected the Brisbane suburb <a href="http://en.wikipedia.org/wiki/The_Gap,_Queensland">The Gap</a> in 2008. </p>
<p>If we just look at days favourable to severe thunderstorms, there is little indication that there is an increasing frequency of severe thunderstorms outside of natural variability since 1979.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/67350/original/image-20141216-14157-1jdcmeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/67350/original/image-20141216-14157-1jdcmeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/67350/original/image-20141216-14157-1jdcmeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=243&fit=crop&dpr=1 600w, https://images.theconversation.com/files/67350/original/image-20141216-14157-1jdcmeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=243&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/67350/original/image-20141216-14157-1jdcmeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=243&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/67350/original/image-20141216-14157-1jdcmeq.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=305&fit=crop&dpr=1 754w, https://images.theconversation.com/files/67350/original/image-20141216-14157-1jdcmeq.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=305&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/67350/original/image-20141216-14157-1jdcmeq.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=305&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 Shelf’ - A shelf cloud associated with a squall line stretches across the Victorian plains near Mitiamo.</span>
<span class="attribution"><span class="source">John Allen</span></span>
</figcaption>
</figure>
<h2>Will severe storms become more common?</h2>
<p>In a warming climate, results for <a href="http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-13-00426.1">Australia</a>, the <a href="http://news.nationalgeographic.com/news/2013/09/130924-global-warming-climate-change-thunderstorms-tornadoes/">United States</a> and Europe have shown that the the surface air becomes warmer and moisture increases, making updrafts stronger, while the wind shear available to organise storms appear to decrease. </p>
<p>This battle between the elements seems to end with the strength of updrafts winning, and results in more days with stronger severe thunderstorms. Over the east coast, projected increases by the end of the 21st century for Melbourne, Sydney and Brisbane range between 114% and 160% of present levels. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/67349/original/image-20141216-14132-1gyxxe7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/67349/original/image-20141216-14132-1gyxxe7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/67349/original/image-20141216-14132-1gyxxe7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/67349/original/image-20141216-14132-1gyxxe7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/67349/original/image-20141216-14132-1gyxxe7.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/67349/original/image-20141216-14132-1gyxxe7.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/67349/original/image-20141216-14132-1gyxxe7.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/67349/original/image-20141216-14132-1gyxxe7.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">‘Crawler of the Dish’ - Lightning crawls through the anvil from a storm near Parkes, NSW while a semi-trailer drives down the road.</span>
<span class="attribution"><span class="source">John Allen</span></span>
</figcaption>
</figure>
<p>Are we certain though? Several factors remain unexplained in a warming climate. </p>
<p>If the air above the surface warms as well, then it is possible that warming the surface won’t result in as many thunderstorms, but they will be stronger. </p>
<p>If we don’t get as many patterns which pull the conditions favourable to thunderstorms together, then maybe the frequency won’t change or will simply shift the season. </p>
<p>It is important to remember that even as the climate changes, our poor knowledge of past events is insufficient to say with any degree of certainty that a severe thunderstorm is beyond what was possible before. </p>
<p>What this change does mean is an increasing likelihood that we will see severe thunderstorms more often, and the question remains as to whether Australia as a nation is prepared to respond.</p><img src="https://counter.theconversation.com/content/35327/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>John Allen is a member of both the Australian Meteorological and Oceanographic Society and the American Meteorological Society. </span></em></p>The supercell that hit Brisbane on November 27 this year caused more than A$500 million worth of damage, produced hail up to 7.5 cm in diameter, and lashed the city with winds of more than 140 km an hour…John Allen, Postdoctoral Research Scientist, Severe Thunderstorms, Tornadoes, Convection & Climate Predictability, Columbia UniversityLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/298712014-07-30T10:11:59Z2014-07-30T10:11:59ZExtreme weather isn’t so unusual – it just depends how far back you remember<figure><img src="https://images.theconversation.com/files/55302/original/v8k5ghwr-1406710652.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">Hail in summer - not so rare.</span> <span class="attribution"><a class="source" href="https://twitter.com/SCRainey2997">@SCRainey2997/Twitter</a></span></figcaption></figure><p>Hail, heavy rain, lightning and flash flooding – not necessarily typical summer weather in southeast England. But the recent <a href="http://news.sky.com/story/1308797/rivers-of-hail-as-freak-storm-sweeps-coast">unexpected deluge</a> saw homes evacuated, stations flooded, and road and rail services interrupted. According to the Met Office, more than half the monthly average total rainfall fell <a href="http://metofficenews.wordpress.com/">in just an hour</a>.</p>
<p>In Hove, Brighton and Worthing, the storm kicked off with a particularly heavy hailstorm leaving many waking up to positively wintry scenes. Such unexpected weather, described as “extreme” in nature, has prompted many to declare that freak weather events are becoming more common and more damaging. But is this <a href="http://www.theweathernetwork.com/uk/news/articles/hailstones-in-summer-actually-its-not-so-weird/32784/">really the case</a>?</p>
<p>The Met Office is an important source of information on the history of weather extremes. Its national weather records can help put current events into an historical context. However, while it can be difficult to make sense of historical meteorological information, the records held at city and county record offices, libraries and archives can provide a human dimension, transforming meteorological data into stories of people and communities.</p>
<p>Those in Sussex affected by the storm used Twitter to share reactions and experiences, whereas in the past letters, diaries, newspapers and official documents recorded the effects of extreme weather. With this documentary archive stretching back hundreds of years we can investigate how one event was described in relation to another, and whether and why they were judged to be unusual or extreme. </p>
<p>The records of Leicestershire County Quarter Sessions document the huge community response to a “dreadful storm of hail” on July 28 1814. A committee was formed to collect subscriptions to provide relief for those who had suffered losses from the storm. From the committee’s papers we know that William Collishaw of Birstall lost a quantity of the fruit from his orchards in the storm, and that John Blockley lost wheat, potatoes, onions and peas to the value of £106. </p>
<p>The same storm is also recorded in the diary of Peter Pegge-Burnell of Winkburn Hall, Nottingham: </p>
<blockquote>
<p>Dull close morn betwixt one & two, loud thunder, some lightg & heavy showers – about six in the afternoon came on the most dreadful hailstorm I ever beheld – a number of hailstones pointd and as large as my thumb end – or first joint – sometime after a continuation of some hours of vivid flashing & constant thunder, a deluge of heavey rain followed – the damage by this horrid storms to my corn, hay, garden & windows is very considerable – thank God no lives lost as I have heard.</p>
</blockquote>
<p>Joseph Woolley, a framework knitter and stocking maker from Nottingham, recorded a hailstorm in his diary entry for August 11, 1809 in which he notes “hail stones seven inches long,” breaking windows in a number of houses at Beeston Rylands. </p>
<p>Records from the Edgbaston Estate papers include a letter from a tenant, E. Whigg, to his landlord’s agent Charles Yates informing him that the severe hailstorm of August 1846 “completely destroyed the windows in the front of our house” and suggesting a change in design (a suggestion rejected by his Landlord).</p>
<p>On July 25, 1900 the Haverfordwest and Milford Haven Telegraph reported on a “terrible hailstorm in Northampton”, when “those of the bigness of the thin-shelled English walnut were the average but hail-stones as big as hens’ eggs were in abundance”.</p>
<p>So extreme summer hailstorms are not without historical precedent in the UK, as recorded in descriptions found in diaries, letters, official documents and newspapers. With many accounts of the same event, it’s possible to build a picture of how people responded. It’s also possible to build up a picture of how certain events enter a community’s cultural memory – the extremely cold and snowy winter of 1947, the extreme heat of the summer of 1976, and the extreme floods of 2007 – while others are quickly forgotten. </p>
<p>In a letter to Lord Manvers dated February 14, 1795, William Sanday at Holme Pierrepont in describing a flood in Nottingham refers back to an earlier flood: </p>
<blockquote>
<p>We have had a most dreadful flood upon the River Trent; it was 3 feet one inch higher than the Midsummer flood, which happened between 50 & 60 years ago; this was ascertained from a mark then made, and which still remains. </p>
</blockquote>
<p>Like many accounts of extreme weather events, William Harwood’s diary entry for February 11, 1795 refers directly to flood memory, “SW wind fine day, the largest flood upon the Trent ever remembered.” </p>
<p>Different ways of recording the past transmit information and awareness of extreme weather across generations, beyond the memory of individual lives. Being aware of extreme events that have occurred in the past can help people comprehend the problems of risk and uncertainty in the face of extreme weather events now and in the future.</p><img src="https://counter.theconversation.com/content/29871/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Lucy Veale receives funding from AHRC.</span></em></p>Hail, heavy rain, lightning and flash flooding – not necessarily typical summer weather in southeast England. But the recent unexpected deluge saw homes evacuated, stations flooded, and road and rail services…Lucy Veale, Research Fellow, University of NottinghamLicensed as Creative Commons – attribution, no derivatives.