tag:theconversation.com,2011:/au/topics/australian-natural-hazards-series-32987/articlesAustralian natural hazards series – The Conversation2018-03-18T18:56:01Ztag:theconversation.com,2011:article/933712018-03-18T18:56:01Z2018-03-18T18:56:01ZFloods don’t occur randomly, so why do we still plan as if they do?<p>Most major floods in South East Queensland arrive in five-year bursts, once every 40 years or so, according to our <a href="https://doi.org/10.1080/13241583.2018.1446677">new research</a>.</p>
<p>Yet <a href="http://arr.ga.gov.au/">flood estimation, protection and management approaches</a> are still designed on the basis that flood risk stays the same all the time – despite clear evidence that it doesn’t.</p>
<p>We analysed historical flooding data from ten major catchments in South East Queensland. As we <a href="https://doi.org/10.1080/13241583.2018.1446677">report in the Australasian Journal of Water Resources</a>, 80% of significant floods arrived during five-year windows, with 35-year gaps of relative dryness between.</p>
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Read more:
<a href="https://theconversation.com/old-floods-show-brisbanes-next-big-wet-might-be-closer-than-we-think-70392">Old floods show Brisbane's next big wet might be closer than we think</a>
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<p>The early 1970s brought a succession of severe floods to South East Queensland. This was followed in the 1980s by a raft of floodplain development projects, together with extensive research on floodplains and flooding risk, carried out by a group of researchers who described themselves as the “Roadshow” because of their frequent visits to flood-prone regions.</p>
<p>Throughout the 1980s, some Roadshow members noticed that large floods in South East Queensland seemed to follow a 40-year cycle, with five-year periods of high flood risk separated by 35 years of lower flood risk. They speculated that the next “1974 flood” (a reference to a <a href="http://www.australiangeographic.com.au/topics/history-culture/2012/03/floods-10-of-the-deadliest-in-australian-history/">devastating flood</a> that hit Brisbane and South East Queensland that year) would arrive some time around 2013 . </p>
<p>Sure enough, South East Queensland was once again hit by <a href="http://www.floodcommission.qld.gov.au/">large floods in January 2011 and January 2013</a>. </p>
<p>Evidently, large floods in South East Queensland are not random. This is a problem, given that development policies and engineering practice, by and large, still assume that they are. </p>
<h2>History repeating</h2>
<p>In 1931, the Queensland meteorologist and farmer <a href="https://en.wikipedia.org/wiki/Inigo_Owen_Jones">Inigo Jones</a> linked the Brisbane River’s floods to the <a href="http://adsabs.harvard.edu/full/2000ESASP.463..517R">Bruckner Cycle</a> of solar activity, which he determined to be 35 years long, but which has <a href="http://onlinelibrary.wiley.com/doi/10.1029/2009RG000282/abstract">since been found to vary from 35 to 45 years</a>.</p>
<p>In 1972, flood engineer John Ward argued that flood frequency distributions differ in space and time because higher flows originate from a variety of different rainfall mechanisms. At the time, minimal insight was available into what those different rainfall mechanisms were.</p>
<p>In the 1990s, drought research in Queensland by, among others, researchers <a href="http://onlinelibrary.wiley.com/doi/10.1002/joc.3370120608/abstract">Roger Stone</a> and <a href="https://www.researchgate.net/publication/265114511_A_Prototype_National_Drought_Alert_Strategic_Information_System_for_Australia">Ken Brook and John Carter</a> identified cyclical variations in Queensland rainfall associated with the <a href="http://www.bom.gov.au/climate/glossary/soi.shtml">Southern Oscillation Index (SOI)</a>, supporting the idea of non-random occurrence of floods. </p>
<p>In 1999, Australian hydrologist Robert French also noticed that irregular clustering of flood events was associated with the SOI, and pointed out that flood planning needed to take into account more than just seasonal or year to year variability.</p>
<p>More recently, flood incidence has been strongly linked to large-scale ocean processes such as the El Niño/Southern Oscillation (ENSO) and the Interdecadal Pacific Oscillation (IPO). These phenomena seem to have a marked effect on <a href="https://theconversation.com/decade-to-decade-changes-in-our-climate-whats-really-going-on-7226">eastern Australian rainfall variability</a>, and therefore on the risk of both <a href="https://theconversation.com/planning-for-a-rainy-day-theres-still-lots-to-learn-about-australias-flood-patterns-68170">floods</a> and <a href="https://theconversation.com/the-lessons-we-need-to-learn-to-deal-with-the-creeping-disaster-of-drought-68172">drought</a>. </p>
<h2>Is the 40-year cycle real?</h2>
<p>We compiled records of major floods in South East Queensland between 1890 and 2014. As the table below shows, roughly 80% of large historical floods happened within a series of five-year flood-prone periods, despite these periods together representing only 16% of the study period.</p>
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<a href="https://images.theconversation.com/files/210246/original/file-20180314-113485-11tnuni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/210246/original/file-20180314-113485-11tnuni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/210246/original/file-20180314-113485-11tnuni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=423&fit=crop&dpr=1 600w, https://images.theconversation.com/files/210246/original/file-20180314-113485-11tnuni.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=423&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/210246/original/file-20180314-113485-11tnuni.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=423&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/210246/original/file-20180314-113485-11tnuni.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=531&fit=crop&dpr=1 754w, https://images.theconversation.com/files/210246/original/file-20180314-113485-11tnuni.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=531&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/210246/original/file-20180314-113485-11tnuni.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=531&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">The South East Queensland study area (approximately indicated by the orange box) and the 10 catchments analysed in this study.</span>
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<a href="https://images.theconversation.com/files/210247/original/file-20180314-113458-cmb810.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/210247/original/file-20180314-113458-cmb810.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/210247/original/file-20180314-113458-cmb810.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=332&fit=crop&dpr=1 600w, https://images.theconversation.com/files/210247/original/file-20180314-113458-cmb810.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=332&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/210247/original/file-20180314-113458-cmb810.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=332&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/210247/original/file-20180314-113458-cmb810.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=417&fit=crop&dpr=1 754w, https://images.theconversation.com/files/210247/original/file-20180314-113458-cmb810.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=417&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/210247/original/file-20180314-113458-cmb810.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=417&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">Timing of the largest flood events within the 40-year cycles. Superscripts next to each flood event indicate the ranking of that flood event in that catchment (that is, the largest flood in each catchment is ranked 1).</span>
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<p>On average, the number of large floods per year was 4.9 times higher within the five-year flood-prone periods.</p>
<p>Not only were floods more frequent, they were also more severe, with flood heights 41% higher during the five-year flood-prone periods than at other times.</p>
<p>Even though a few large floods occurred outside the five-year flood-prone periods, the 40-year cycle of flooding in South East Queensland appears to be a genuine phenomenon. </p>
<h2>What drives the cycle?</h2>
<p>The most likely physical explanation for cyclic or non-random flooding is the <a href="https://link.springer.com/article/10.1007/s003820050284">IPO</a>, which is rather like the ENSO cycle except on longer time scales. The IPO influences eastern Australia’s climate indirectly, by affecting both the magnitude and frequency of ENSO impacts. </p>
<p>Recent <a href="https://link.springer.com/article/10.1007/s00382-015-2525-1">“negative phases” of the IPO</a> – meaning warmer than average Pacific Ocean temperatures north and south of the tropics – happened roughly during 1870–95, 1945-76, and 1999–present.</p>
<p>If we compare these with the five-year flood-prone periods in the table above, we can see that with the exception of 1930–34, all five-year flood-prone periods happened during these negative IPO events. Interestingly, the large floods in the 1950s and 1960s happened outside the five-year flood-prone periods identified by the 1980s Roadshow, but do align with IPO negative conditions. </p>
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Read more:
<a href="https://theconversation.com/planning-for-a-rainy-day-theres-still-lots-to-learn-about-australias-flood-patterns-68170">Planning for a rainy day: there's still lots to learn about Australia's flood patterns</a>
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<p>In spite of all this evidence, most engineers and flood planners still assume that floods occur randomly and that flood risk is the same all the time. Phrases like “one in 100-year event” or “1% annual exceedance probability” are routinely used to describe floods, despite the fact that for some years and decades the risk is significantly higher. This gives a false sense of security during times when major floods are much more likely.</p>
<p>If this approach continues, then every few decades our flood defences will not be as reliable as we thought – a fact to which many Queenslanders can now attest.</p>
<p>We need new approaches to deal with the reality that large flood events do not occur randomly. It would arguably be more sensible to separate flood records into two (or more) categories – one for times when flood risk is “normal” and another for periods where the risk is higher – and then reevaluate flood frequency distributions and flood risks for each category. Decision makers then get a more realistic estimate of the true risk of flooding which leads to more informed and more resilient flood planning and defences.</p>
<p>This new approach might also help plan for the changes to flood risk expected in the future, whether from climate change, land use change, or whatever else the oceans and skies throw at us. </p>
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<p><em>This article was coauthored by Greg McMahon, a Brisbane-based independent consultant on flood risks and <a href="http://www.rhodesgroup.com.au/meet-the-advisory-board/">Academic Chair at Rhodes Group Australia</a>.</em></p><img src="https://counter.theconversation.com/content/93371/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Anthony Kiem receives funding from Australian Research Council (ARC).</span></em></p>Engineering practice assumes that floods are randomly distributed but science suggests they are not. This raises questions about the reliability of flood infrastructure and management strategies.Anthony Kiem, Associate Professor – Hydroclimatology, University of NewcastleLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/683482016-11-14T22:43:27Z2016-11-14T22:43:27ZHurt by sea: how storm surges and sea-level rise make coastal life risky<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.</em></p>
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<p>Australia is a huge continent, but a coastal nation. About 80% of Australians live within 50km of the coast, and a sea-level rise of 1.1 metres (a high-end scenario for 2100) would put about A$63 billion (in 2008 dollars) worth of residential buildings at risk. </p>
<p>Anyone who lives along Sydney’s northern beaches, especially in <a href="http://www.abc.net.au/news/2016-06-16/engineers-waiting-for-collaroy-residents-to-have-houses-cleared/7516184">Collaroy</a>, saw at first hand the damage the ocean can wreak on coastal properties when the coastline was hit by a severe <a href="https://theconversation.com/explainer-the-wild-storms-that-lash-australias-east-coast-40564">east coast low</a> during a king tide in June.</p>
<p>There are many different factors that determine which coastal homes or suburbs are most at risk of inundation or erosion, either now or in the future. In a <a href="http://link.springer.com/article/10.1007/s10584-016-1647-8">review</a> published as part of a series produced by the <a href="http://ozewex.org">Australian Energy and Water Exchange</a> initiative, we investigated the causes of extreme sea levels and coastal impacts in Australia, how they have changed, and how they might change even more. While significant progress has been made over recent decades, many questions remain.</p>
<p>The first factor to consider is the average sea level, relative to the land elevation. This “background” sea level varies, both from year to year and season to season. Depending on where you live and what the climate is doing, background sea level can fluctuate by up to about 1m. Around Australia’s northern coastline, for example, El Niño and La Niña can cause large variations in year-to-year sea levels. </p>
<p>On top of this are the tides, which rise and fall predictably, and whose range varies by location and phase of the moon. Most places have two tides a day, but curiously <a href="http://link.springer.com/article/10.1007/s10584-016-1647-8">some only have one - including Perth</a>. </p>
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<span class="caption">Map of tide pattern variations. Red: one high and low tide daily (diurnal); blue: two high and low tides per day (semi-diurnal) with a mixed tidal regime between.</span>
<span class="attribution"><span class="source">OZEWEX</span>, <span class="license">Author provided</span></span>
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<p>On top of that again is the effect of the weather, the most notable short-term effects being storm surges and storm waves. During a surge, the storm pushes extra water onto the coast through a combination of wind pressure, wave buildup, and atmospheric pressure changes. Obviously these factors are much more localised than tides.</p>
<p>Extreme sea-level events, such as the one that hit Sydney in June, can arise from isolated events such as a storm surge. But more often they are due to a combination of natural phenomena that on their own may not be considered extreme. In Sydney, several factors aligned: a storm surge driven by an <a href="https://theconversation.com/explainer-the-wild-storms-that-lash-australias-east-coast-40564">east coast low</a>, an uncommon wave direction, a king tide, and a higher-than-average background sea level.</p>
<p>These processes already have the capacity to destroy coastal homes and infrastructure. But for the future, we also need to factor in climate change, which will raise the background sea level and may also change the frequency and intensity of storms.</p>
<h2>Long-term trends</h2>
<p>Average sea levels in Australian waters have been rising at rates similar to (but just below) the global average. Since 1993, <a href="http://www.bom.gov.au/oceanography/projects/abslmp/abslmp.shtml">Australian tide gauges</a> show an average rise of 2.1mm per year, whereas <a href="http://www.cmar.csiro.au/sealevel/sl_hist_last_decades.html">satellite observations</a> reveal a global average rise of 3.4mm per year. </p>
<p>What really counts is extreme sea levels, and these have been rising at <a href="http://onlinelibrary.wiley.com/doi/10.1029/2009JC005997/full">roughly the same rate</a>, meaning that the rising background sea level is a fairly good guide to how extremes are increasing. </p>
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<span class="caption">The effects of a king tide on Queensland’s Gold Coast.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File%3ACSIRO_ScienceImage_10726_The_effects_of_a_king_tide_on_Queenslands_Gold_Coast.jpg">Bruce Miller/CSIRO</a>, <a class="license" href="http://creativecommons.org/licenses/by/4.0/">CC BY</a></span>
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<p>This trend will continue in the future, although more energetic storm systems may also cause larger storm surges and hence higher rates of extreme sea levels in some places. More frequent storms are also set to make extreme sea-level events more common.</p>
<p>By 2100, global average sea level is <a href="http://www.ipcc.ch/report/ar5/wg1/">projected</a> to rise by 0.28-0.61m, relative to the period 1986-2005, if this century’s global warming can be held to about 1°C. But if greenhouse emissions continue to increase at their current rate, the world is in line for sea-level rises of 0.52-0.98m. </p>
<p>This rise will not be uniform around Australia’s coastline. The east coast is likely to experience up to 6cm more sea-level rise than the global average by 2100, because of the expected warming and strengthening of the East Australian Current.</p>
<p>Trends in Australia’s weather and waves are harder to predict. <a href="http://science.sciencemag.org/content/332/6028/451">Satellite measurements</a> over the past 30 years suggest that waves are getting slightly higher in the Southern Ocean, and climate models suggest that <a href="http://www.nature.com/nclimate/journal/v3/n5/full/nclimate1791.html">this may continue</a>. As the tropics continue to expand with climate change, the band of westerly winds over the Southern Ocean will retreat further south and strengthen, whipping up higher waves that will travel to Australia’s southern coast as swell. On the other hand, weakening winds nearer to Australia may help to dampen down wave heights. On Australia’s eastern coast, climate models suggest fewer large wave events <a href="http://www.nature.com/nclimate/journal/v4/n4/full/nclimate2142.html">due to decreasing storminess in the Tasman Sea in the future</a>. </p>
<p>A significant challenge we face is not having the data available to monitor the changes along our southern coastline. Australia has the longest east-west continental shelf in the world, but we have only a handful of wave buoys to measure these processes; much of the coastline is not monitored despite widespread coastal management concerns.</p>
<p>Our understanding of extreme sea-level change in Australia is also limited by available tide gauge coverage. Only two digital tide gauge records (in <a href="http://www.psmsl.org/data/obtaining/stations/111.php">Fremantle</a> and <a href="http://www.psmsl.org/data/obtaining/stations/65.php">Fort Denison</a>) extend back to at least the early 20th century, and records elsewhere around the coast typically span less than 50 years. </p>
<p>However, our investigation discovered that there is an opportunity to increase the length of available records by digitising old paper tide gauge charts. This could extend several records along our southern and tropical coastlines.</p>
<p>We also have major gaps in our knowledge about how our coastlines will be changed by flooding and erosion. The simple methods used to predict coastal erosion may <a href="http://www.nature.com/nclimate/journal/v3/n1/abs/nclimate1664.html">underestimate erosion significantly, particularly in estuaries</a>. </p>
<p>Given the considerable urban infrastructure located within estuaries, and the fact that they are vulnerable both to coastal storms and river floods, this is one of the many crucial questions about life on the coast that we still need to answer.</p><img src="https://counter.theconversation.com/content/68348/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Kathleen McInnes works for CSIRO Oceans and Atmosphere, and receives funding from the Commonwealth of Australia Department of the Energy and Environment National Environmental Science Program, through the Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency.</span></em></p><p class="fine-print"><em><span>Mark Hemer works for CSIRO Oceans and Atmosphere, and receives funding from the Commonwealth of Australia Department of the Energy and Environment National Environmental Science Program, through the Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency. </span></em></p><p class="fine-print"><em><span>Ron Hoeke works for CSIRO Oceans and Atmosphere, and receives funding from the Commonwealth of Australia Department of the Energy and Environment National Environmental Science Program, through the Earth Systems and Climate Change Hub, and the Australian Renewable Energy Agency.</span></em></p>Many Australians live on the coast, but how much do we know about the risks? While average sea levels are relatively easy to gauge, the risk of flooding also depends on weather, landscape, and climate.Kathleen McInnes, Senior research scientist, CSIROMark Hemer, Senior Research Scientist, Oceans and Atmosphere, CSIRORon Hoeke, Littoral oceanographer, CSIROLicensed 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/684262016-11-10T19:14:16Z2016-11-10T19:14:16ZFirestorms: the bushfire/thunderstorm hybrids we urgently need to understand<figure><img src="https://images.theconversation.com/files/145372/original/image-20161110-26340-15r4qm0.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The higher the plume, the bigger the problem.</span> <span class="attribution"><span class="source">Jim Peaco/Wikimedia Commons</span></span></figcaption></figure><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>
<hr>
<p>Fire has been a driving force across Australia for millennia. Indeed, the health of many of our ecosystems is intrinsically dependent on fire. But bushfires are also one of our most frequent natural hazards, with a total cost estimated at <a href="http://www.tandfonline.com/doi/abs/10.1080/13669870802648528">A$340 million per year</a>. </p>
<p>In the past decade or so, extreme bushfires in southeastern Australia have burned <a href="http://link.springer.com/article/10.1007/s10584-016-1811-1">more than a million hectares, claiming more than 200 lives and over 4,000 homes</a>. Similar losses in other major urban areas have prompted questions about whether we are seeing a shift towards a significantly more hazardous fire regime, characterised by increasing fire frequency and intensity, and the development of catastrophic “firestorms”. </p>
<p>While these extreme bushfires account for only a very small percentage of fire events, they are responsible for the lion’s share of bushfire-related losses.</p>
<p>In contrast to typical bushfires, which spread across the landscape as well-defined burning fronts with smoke plumes perhaps a few kilometres high, extreme bushfires exhibit deep and widespread flaming and produce smoke plumes that can extend 10-15km into the atmosphere. </p>
<p>At these altitudes, bushfire plumes can actually develop into thunderstorms (hence the term “firestorm”). As such, extreme bushfires become much more difficult for emergency services to handle, making them all but impossible to suppress and their spread difficult to predict. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/145371/original/image-20161110-26318-5ykpxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/145371/original/image-20161110-26318-5ykpxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/145371/original/image-20161110-26318-5ykpxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=400&fit=crop&dpr=1 600w, https://images.theconversation.com/files/145371/original/image-20161110-26318-5ykpxx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=400&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/145371/original/image-20161110-26318-5ykpxx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=400&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/145371/original/image-20161110-26318-5ykpxx.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=503&fit=crop&dpr=1 754w, https://images.theconversation.com/files/145371/original/image-20161110-26318-5ykpxx.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=503&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/145371/original/image-20161110-26318-5ykpxx.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=503&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">A firestorm blots out the sky in Victoria’s Grampians.</span>
<span class="attribution"><span class="source">Randall Bacon</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<h2>Beyond hot, dry and windy</h2>
<p>Like other dangerous bushfires, firestorms are driven by hot, dry and windy weather. But to spawn a firestorm, a range of other conditions must also be met; these can include a rugged landscape, particularly nasty weather events that produce “spikes” in fire danger, and conditions in the upper atmosphere that allow fire plumes to grow to considerable heights. </p>
<p>While previous studies have considered past and projected changes in the hot, dry and windy aspect of fire danger, less research has been done on the future projections for these other types of conditions. This means that we have quite a poor understanding of how extreme bushfires might affect us in the future.</p>
<p>As part of a series of reviews produced by the <a href="http://ozewex.org/">Australian Energy and Water Exchange</a> initiative, my colleagues and I have taken a <a href="http://link.springer.com/article/10.1007/s10584-016-1811-1">closer look</a> at the most catastrophic bushfire cases and the factors that drive them, beyond the usual hot, dry and gusty weather.</p>
<p>There has been an overall increase in the frequency of major bushfire events in southeastern Australia since the mid-19th century. In particular, in the past 15 years a major fire event has occurred every 5 years or less. While some of this increase is due to changes in land use since European colonisation, there is also strong evidence of climate-driven changes. </p>
<p>We found that besides increases in dangerous surface fire danger conditions, upper atmospheric conditions have also become more conducive to explosive fire growth. High levels of the <a href="http://www.highfirerisk.com.au/tools/c_haines_flierA4.pdf">c-Haines index</a>, which signals greater potential for a fire’s plume to rise high into the atmosphere, have become considerably more prevalent since the 1980s. The effects of droughts and widespread heatwaves have also contributed to the occurrence of extreme bushfires.</p>
<p>Looking into the future, high c-Haines values are projected to grow more prevalent still, albeit more gradually than over recent decades. Frontal weather patterns associated with particularly bad fire days are also projected to become more frequent during this century, and rainfall is projected to decrease over southwest and southeastern Australia. </p>
<p>All of this suggests that extreme bushfires will become a more common occurrence into the future. </p>
<h2>What we still don’t know</h2>
<p>Our methods for assessing fire danger do not explicitly account for the effects of extended drought and heatwaves on larger fuel elements such as branches and logs, and so may not properly account for their effects on fire spread and heat release into the atmosphere.</p>
<p>There is also considerable uncertainty about how fuel loads will change into the future. It is possible that the higher fire intensities expected to result from the direct effects of a warmer, drier climate may be offset by lower fuel loads.</p>
<p>Our understanding of extreme fire occurrence is also hampered by the lack of long-term and prehistoric climate data, which makes it hard to work out what the “normal” level of extreme bushfires has been in the past. While charcoal records show promise in this regard, we still don’t know enough about how charcoal is generated, deposited and subsequently preserved during extreme fires.</p>
<p>To predict the future occurrence of extreme bushfires, we also have more work to do in understanding how the trends forecast by global climate models will play out in terms of creating regional-scale fire weather conditions. And we still need to figure out the likely effects of other large-scale patterns such as El Niño.</p>
<p>Given the relatively recent advances that have been made in understanding the key drivers of extreme bushfires, the field is now ready for targeted studies that will help us estimate the future risk of extreme bushfires – and how best we can confront the threat.</p>
<hr>
<p><em>This article was amended on November 11, 2016, to correct the figure for the cost of bushfire-related damage. The correct figure is A$340 million, not A$8.5 billion which is the annual cost of all fire-related damage in Australia.</em></p><img src="https://counter.theconversation.com/content/68426/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Jason Sharples receives funding from the Australian Research Council and the Bushfire and Natural Hazards Cooperative Research Centre. </span></em></p>When a bushfire rages so high it creates its own thunderstorm, it becomes a ‘firestorm’ - and makes life much more difficult for firefighters. We still have a lot to learn about what triggers them.Jason Sharples, Associate Professor, School of Physical, Environmental and Mathematical Sciences, UNSW Australia, UNSW SydneyLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/681742016-11-09T19:07:42Z2016-11-09T19:07:42ZWe’ve learned a lot about heatwaves, but we’re still just warming up<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 part of a <a href="https://theconversation.com/au/topics/australian-natural-hazards-series-32987">series</a> looking at those threats in detail.</em></p>
<hr>
<p>Australia is no stranger to heatwaves. Each summer, large areas of the continent fry under intense heat for days on end, causing <a href="http://www.abc.net.au/news/2014-01-15/fire-crews-on-alert-as-south-east-australia-sizzles-in-heatwave/5200424">power outages</a>, <a href="http://www.watoday.com.au/wa-news/perth-weather-sevenday-heatwave-starts-thursday-20160204-gmlfg8.html">public transport delays</a>, and severe impacts to <a href="https://www.healthdirect.gov.au/hot-weather-risks-and-staying-cool">human health</a>. The estimated impact on our workforce alone is <a href="http://www.nature.com/nclimate/journal/v5/n7/full/nclimate2623.html">US$6.2 billon per year</a>. Heatwaves are also Australia’s deadliest natural hazard, accounting for <a href="http://www.sciencedirect.com/science/article/pii/S1462901114000999">well over half</a> of all natural disaster-related deaths.</p>
<p>Along with our colleagues, we have taken a <a href="http://link.springer.com/article/10.1007/s10584-016-1650-0">close look</a> at what we know and don’t know about heatwaves in Australia, as part of a series of reviews produced by the <a href="http://ozewex.org/">Australian Energy and Waster Exchange initiative</a>.</p>
<p>Let’s start with the stuff we know. First, we are very clear on the weather systems that drive heatwaves in Australia’s densely populated coastal areas. Typically, a persistent high-pressure system sits <a href="http://onlinelibrary.wiley.com/doi/10.1002/2014GL061736/abstract">next to the region experiencing the heatwave</a>, pushing hot air from the centre of Australia towards that region. The location of the high depends on the region experiencing the heatwave, but there is always one there.</p>
<p>These high-pressure systems are created and sustained by other weather influences farther afield, for instance. We know for instance that heatwaves in Melbourne are <a href="http://onlinelibrary.wiley.com/doi/10.1002/2013GL058257/full">coupled with tropical cyclones</a> to the northwest of Australia.</p>
<p>Other, longer-term variables can affect not just individual heatwaves but their patterns, timing and severity too. So heatwaves are likely to be much longer and more frequent <a href="http://onlinelibrary.wiley.com/doi/10.1002/2015JD023592/full">during El Niño</a> than La Niña phases over much of northern and eastern Australia. However, this does not influence heatwaves <a href="http://onlinelibrary.wiley.com/doi/10.1002/2014GL061736/full">over Australia’s far southeast</a> – here, the most important driver is changes to <a href="http://www.bom.gov.au/climate/enso/history/ln-2010-12/SAM-what.shtml">wind patterns over the Southern Ocean</a>.</p>
<p>We also know that heatwave trends have increased in the observational record, and, unfortunately, that they will continue to do so. By far the strongest trend is in the number of heatwave days experienced each season. Over much of eastern Australia, this trend is as large as <a href="http://www.climatecouncil.org.au/heatwaves-report">two extra days per season, per decade</a>.</p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/144993/original/image-20161108-4688-1wuhp5p.png?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/144993/original/image-20161108-4688-1wuhp5p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/144993/original/image-20161108-4688-1wuhp5p.png?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=480&fit=crop&dpr=1 600w, https://images.theconversation.com/files/144993/original/image-20161108-4688-1wuhp5p.png?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=480&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/144993/original/image-20161108-4688-1wuhp5p.png?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=480&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/144993/original/image-20161108-4688-1wuhp5p.png?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=603&fit=crop&dpr=1 754w, https://images.theconversation.com/files/144993/original/image-20161108-4688-1wuhp5p.png?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=603&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/144993/original/image-20161108-4688-1wuhp5p.png?ixlib=rb-1.1.0&q=15&auto=format&w=754&h=603&fit=crop&dpr=3 2262w" sizes="(min-width: 1466px) 754px, (max-width: 599px) 100vw, (min-width: 600px) 600px, 237px"></a>
<figcaption>
<span class="caption">Trends in seasonal heatwave days, per decade.</span>
<span class="attribution"><span class="source">Perkins-Kirkpatrick et al., Climatic Change</span>, <span class="license">Author provided</span></span>
</figcaption>
</figure>
<p>Looking <a href="http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00092.1">into the future</a>, heatwaves are projected to become more frequent, with increases of between 20 and 40 extra days per season in the north and 5-10 extra days in the south likely by the end of this century, under a “business as usual” scenario. The intensity of heatwaves over southern Australia is also increasing faster than the average temperature. This is not good news for our ageing population, our fragile ecosystems and our outdated infrastructure.</p>
<p>The Australian research community has been successful in leading the development of a comprehensive way to measure <a href="http://www.sciencedirect.com/science/article/pii/S0079661116000057">marine heatwaves</a>. Just like the atmosphere, areas of the ocean can experience prolonged periods of abnormally warm temperatures. These marine heatwaves can be every bit as damaging as atmospheric ones, decimating marine habitats and killing coral.</p>
<h2>What we don’t yet know</h2>
<p>Perhaps surprisingly, given the amount of research and public attention that heatwaves attract, they still do not have an official definition. The Bureau of Meteorology uses a concept called <a href="http://www.cawcr.gov.au/technical-reports/CTR_060.pdf">excess heat factor</a>, which looks at maximum temperatures and ensuing minimum temperatures over a three-day period, incorporating the key characteristic of heatwaves of heat tending to persist overnight. However, we still do not have a universal definition that fits all situations.</p>
<p>We are also unclear on how the physical mechanisms that drive heatwaves will change under ongoing greenhouse warming. <a href="http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00098.1">Recent research</a> suggests that background warming will predominantly drive future increases in heatwaves, with some heatwave-inducing systems moving further south. But we don’t really know how future changes to patterns such as El Niño will continue to influence our heatwaves.</p>
<p>We also don’t really understand the extent to which the land surface drives Australian heatwaves. <a href="http://www.nature.com/ngeo/journal/v7/n5/abs/ngeo2141.html">European studies</a> have shown that dry conditions leading up to heatwave season, resulting in more parched soils, are a recipe for more intense and longer events, particularly when coupled with a persistent high-pressure system. </p>
<p>For Australia, we know that <a href="http://onlinelibrary.wiley.com/doi/10.1002/qj.2596/full">dry soil contributed</a> to the deadly heatwave that preceded the Black Saturday bushfires in 2009. But more extensive studies are needed to understand this complex relationship over Australian soil (pun intended).</p>
<p>We also need a more comprehensive understanding of marine heatwaves. So far there has been only a handful of studies describing <a href="http://www.sciencedirect.com/science/article/pii/S0079661113002425">individual events</a>. We still don’t know how much marine heatwaves have increased over recent decades, or how their causes and severity will change in the future. Given how vulnerable we are to marine heatwaves here in Australia, this topic should be a national research priority.</p>
<p>Finally, we need to develop more practical predictions of how heatwaves are likely to affect people in the future. We know how bad the impacts of heatwaves can be, and we know in general terms how heatwaves will change in the future. Yet the vast majority of our projections come from <a href="http://journals.ametsoc.org/doi/abs/10.1175/JCLI-D-14-00092.1">global climate models</a>. Forecasting the exact impacts calls for finer spatial detail, using regional climate models. But these models are far more computationally expensive to run, and more investment into this area is necessary.</p>
<p>There is no doubt that heatwaves have been, and will continue to be, an integral feature of Australia’s climate, and recent research has taught us a lot about them. But there is more work to be done if we want to safeguard Australians properly from their deadly impacts in the future.</p><img src="https://counter.theconversation.com/content/68174/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Sarah Perkins-Kirkpatrick receives funding from the Australian Research Council.</span></em></p><p class="fine-print"><em><span>Christopher J. White receives funding from various Tasmanian State Government research funding programs, Wine Australia and the Bushfire and Natural Hazard CRC.</span></em></p>Heatwaves are Australia’s deadliest type of natural disaster. But while we know a lot about the weather patterns behind them, more research is needed to forecast accurately their impacts on people.Sarah Perkins-Kirkpatrick, Research Fellow, UNSW SydneyChristopher J White, Lecturer in Environmental Engineering, University of TasmaniaLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/681722016-11-08T19:04:28Z2016-11-08T19:04:28ZThe lessons we need to learn to deal with the ‘creeping disaster’ of drought<figure><img src="https://images.theconversation.com/files/144988/original/image-20161108-4711-eg80dc.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=496&fit=clip" /><figcaption><span class="caption">The Millennium drought had a huge impact on the Murray-Darling river system.</span> <span class="attribution"><span class="source">suburbanbloke/Flickr/Wikimedia Commons</span>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span></figcaption></figure><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>Droughts are a natural feature of the Australian environment. But the <a href="https://theconversation.com/australia-is-not-ready-for-the-next-big-dry-12819">Millennium drought (or “Big Dry”)</a>, which ran from 1997 to 2010, was a wake-up call even by our parched standards. </p>
<p>The Millennium drought had <a href="http://onlinelibrary.wiley.com/doi/10.1002/wrcr.20123/abstract">major social, economic and environmental impacts</a>). It triggered water restrictions in major cities, and prompted severe reductions in irrigation allocations throughout the vast <a href="https://theconversation.com/as-drought-looms-the-murray-darling-is-in-much-healthier-shape-just-dont-get-complacent-50063">Murray-Darling Basin</a>.</p>
<p>The Millennium drought also highlighted that, compared to the rest of the world, the impacts of drought on Australia’s society and economy are particularly severe. This is mainly because our water storage and supply systems were originally designed by European settlers who failed to plan for the huge variability in Australia’s climate.</p>
<h2>Have we learned the lessons?</h2>
<p>Are we likely to fare any better when the next Big Dry hits? It’s important to reflect on how much we actually understand drought in Australia, and what we might expect in the future.</p>
<p><a href="http://link.springer.com/article/10.1007/s10584-016-1798-7">Our study</a>, part of the Australian Water and Energy Exchanges Initiative (<a href="http://www.ozewex.org">OzEWEX</a>), had two aims related to this question. The first was to document what is known and unknown about drought in Australia. The second aim was to establish how Australia’s scientists and engineers can best investigate those unknowns.</p>
<p>The fact is that despite their significance, droughts are <a href="https://theconversation.com/el-nino-is-here-and-that-means-droughts-but-they-dont-work-how-you-might-think-47866">generally still poorly understood</a>. This makes it hard to come up with practical, effective strategies for dealing with them when they strike. </p>
<p>One reason for this is that unlike natural hazards with more graphic and measurable impacts (such as floods, cyclones, and bushfires), droughts develop gradually over huge areas, and can last for years. Often they go unnoticed until they trigger widespread water or food shortages, or cause significant energy, economic, health or environmental issues. </p>
<figure class="align-center zoomable">
<a href="https://images.theconversation.com/files/145003/original/image-20161108-4694-1yu2xzh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=1000&fit=clip"><img alt="" src="https://images.theconversation.com/files/145003/original/image-20161108-4694-1yu2xzh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&fit=clip" srcset="https://images.theconversation.com/files/145003/original/image-20161108-4694-1yu2xzh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=600&h=399&fit=crop&dpr=1 600w, https://images.theconversation.com/files/145003/original/image-20161108-4694-1yu2xzh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=600&h=399&fit=crop&dpr=2 1200w, https://images.theconversation.com/files/145003/original/image-20161108-4694-1yu2xzh.jpg?ixlib=rb-1.1.0&q=15&auto=format&w=600&h=399&fit=crop&dpr=3 1800w, https://images.theconversation.com/files/145003/original/image-20161108-4694-1yu2xzh.jpg?ixlib=rb-1.1.0&q=45&auto=format&w=754&h=501&fit=crop&dpr=1 754w, https://images.theconversation.com/files/145003/original/image-20161108-4694-1yu2xzh.jpg?ixlib=rb-1.1.0&q=30&auto=format&w=754&h=501&fit=crop&dpr=2 1508w, https://images.theconversation.com/files/145003/original/image-20161108-4694-1yu2xzh.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>
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<span class="caption">By the time you know it’s arrived, a drought can already be doing damage.</span>
<span class="attribution"><a class="source" href="https://commons.wikimedia.org/wiki/File%3ASheep_on_a_drought-affected_paddock.jpg">Bidgee/Wikimedia Commons</a>, <a class="license" href="http://creativecommons.org/licenses/by-sa/4.0/">CC BY-SA</a></span>
</figcaption>
</figure>
<p>Drought has been described as a “<a href="http://onlinelibrary.wiley.com/doi/10.1002/wat2.1085/abstract">creeping disaster</a>”, because by the time a drought is identified, it is usually already well under way, the costs to fix it are mounting, and the opportunity to take proactive action has already been missed. </p>
<p>This is complicated still further by the uncertainties around defining, monitoring and forecasting drought – including predicting when a drought will finally end. As in the case of other natural hazards (such as drought’s polar opposite, <a href="https://theconversation.com/planning-for-a-rainy-day-theres-still-lots-to-learn-about-australias-flood-patterns-68170">floods</a>), what we need most is accurate and practically useful information on the likelihood, causes and consequences of droughts in particular areas. </p>
<p>This is a very tricky question, not least because we still need to come up with a rigorous way to distinguish between correlation and causation. For example, are increased local temperatures a <a href="https://theconversation.com/el-nino-is-here-and-that-means-droughts-but-they-dont-work-how-you-might-think-47866">cause or a consequence</a> of drought? </p>
<p>The complications don’t end there. Because droughts are so much <a href="http://onlinelibrary.wiley.com/doi/10.1029/2009GL041067/abstract">slower and bigger</a> than other natural disasters, they therefore have much more complicated effects on agriculture, industry and society. Bushfires can be devastating, but they also offer ample opportunities to learn lessons for the next time. Droughts, in contrast, give us <a href="http://onlinelibrary.wiley.com/doi/10.1002/wrcr.20123/abstract">limited opportunities to learn how best to prepare</a>. </p>
<p>Yet prepare we must. Given Australia’s history of <a href="https://theconversation.com/antarctic-ice-shows-australias-drought-and-flood-risk-is-worse-than-thought-59165">decades-long swings between wet and dry</a>, and the fact that these swings are <a href="http://www.csiro.au/state-of-the-climate">projected to grow even stronger</a>, drought will be a key concern for Australia for a long time to come.</p>
<h2>What to do next</h2>
<p>We therefore make several recommendations to help boost our understanding and management of drought. </p>
<p>1). Reconsider the way drought is defined and monitored to remove confusion between drought causes, impacts and risks. Similarly, there is also a need to better distinguish between drought, aridity, and water scarcity due to over-extractions. </p>
<p>The simplest definition of “drought” is a deficit of water compared with normal conditions. But what is normal? How long does the deficit have to persist, and how severe does it need to be, to be considered a drought? What is meant by water: rainfall, snow, ice, streamflow, water in a storage reservoir, groundwater, soil moisture, or all of these? </p>
<p>The answers to these questions depend very much on the local situation in terms of climate and water use, which varies significantly in space and time and is why the simplest definition of drought is insufficient. We need to develop drought definitions that clearly differentiate drought from long-term changes in aridity and water scarcity, and that capture drought start, duration, magnitude and spatial extent. Such definitions should account for the differences between Australia’s climate zones, the wide variety of end-users and applications of drought monitoring information, and the diversity of droughts that have occurred in the past. There needs to be a common understanding of what a drought is and the differences between drought, aridity and human-induced water scarcity.</p>
<p>2). Improve documentation of droughts that took place before weather records began, in roughly 1900. This will improve our understanding of Australia’s long-term “baseline” drought characteristics (that is, how bad can droughts get? how does the worst drought on record compare with the worst that has ever occurred?), and thus provide the fundamental information needed to successfully manage droughts. </p>
<p>This requires compilation of longer-term and more spatially complete drought histories via the merging of palaeoclimate information with instrumental, satellite, and reanalysis data. This will help us better understand instrumental and pre-instrumental drought behaviour, and put the droughts observed in the instrumental record into context. This work will involve looking at <a href="https://theconversation.com/antarctic-ice-shows-australias-drought-and-flood-risk-is-worse-than-thought-59165">ice cores</a>, <a href="http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0128533">tree rings</a>, <a href="http://onlinelibrary.wiley.com/doi/10.1002/2015WR017062/abstract">different tree rings</a>, <a href="http://onlinelibrary.wiley.com/doi/10.1002/2015WR017059/full">cave deposits</a>, <a href="http://onlinelibrary.wiley.com/doi/10.1029/2005GL025052/abstract">corals</a>, <a href="http://ozewex.org/?p=1506">sediments</a> and <a href="http://www.thebigflood.com.au/">historical changes to river channels and floodplains</a>.</p>
<p>3). Improve drought forecasting by developing more realistic models of the many factors that cause (or contribute to) drought. This will help us separate out the influences of natural variability and human-induced climate change, which in turn will help us make more accurate long-term projections.</p>
<p>If we can answer these big research questions, we will all be better prepared when the next big dry inevitably arrives.</p><img src="https://counter.theconversation.com/content/68172/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Anthony Kiem receives funding from the Australian Research Council and the National Climate Change Adaptation Research Facility. </span></em></p><p class="fine-print"><em><span>Fiona Johnson receives funding from the Australian Research Council and World Health Organisation.</span></em></p><p class="fine-print"><em><span>Seth Westra receives funding from the Australian Research Council and various State Government research funding programs. </span></em></p>Droughts are much bigger and slower than other natural disasters that hit Australia - meaning that despite their huge impacts, we still haven’t figured out how best to protect ourselves.Anthony Kiem, Associate Professor – Hydroclimatology, University of NewcastleFiona Johnson, Senior Lecturer, School of Civil and Environmental Engineering, UNSW SydneySeth Westra, Associate Professor, School of Civil, Environmental and Mining Engineering, University of AdelaideLicensed as Creative Commons – attribution, no derivatives.tag:theconversation.com,2011:article/681702016-11-07T19:06:50Z2016-11-07T19:06:50ZPlanning for a rainy day: there’s still lots to learn about Australia’s flood patterns<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 the first in 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>Recent floods in <a href="http://www.abc.net.au/news/2016-09-23/forbes-expecting-major-flood-residents-urged-to-prepare/7870582">New South Wales</a>, <a href="http://www.abc.net.au/news/2016-09-14/sa-homes-flooded-creeks-and-rivers-still-to-peak-ses-warns/7845572">South Australia</a> and <a href="http://www.abc.net.au/news/2016-09-15/victoria-weather-farmer-missing-homes-under-threat-avoca-river/7846214">Victoria</a> have reminded us of the power of our weather and rivers to wreak havoc on homes, business and even, tragically, lives. </p>
<p>As Dorothea Mackellar <a href="http://www.dorotheamackellar.com.au/archive/mycountry.htm">poetically pointed out</a>, “droughts and flooding rains” have been a feature of Australia throughout history, so maybe we shouldn’t be all that surprised when they happen.</p>
<p>However, we also know that the reported costs of flooding in Australia have been <a href="http://www.emdat.be/">increasing</a>, most likely through a combination of increased reporting, increased exposure through land use change and population growth, and changes to flood magnitude and severity. So it is critical that we understand what might be causing these changes.</p>
<p>This was the question we asked in our <a href="http://link.springer.com/article/10.1007/s10584-016-1689-y">review</a> on how flood impacts have changed over time in Australia and how they may change in the future. We found that despite decades of research in these areas, there are still many gaps in what we know.</p>
<h2>Copping a soaking</h2>
<p>We know that floods depend not just on how much rain falls, but also on how wet the ground is before a heavy rainfall, and how full the rivers are. We also have evidence that the storms that generate heavy rainfall will become more intense in the future, because as the atmosphere warms it can hold <a href="https://theconversation.com/why-warmer-storms-could-lead-to-more-flooding-than-expected-42825">more moisture</a>. </p>
<p>This is particularly the case for storms that last just a few hours; in fact we think that these storms are the most likely to show the largest increases. In urban environments this translates to an even greater flood risk, because the concrete and hard surfaces allow this intense rain to run off quickly through storm drains and into creeks and rivers, rather than seeping into the landscape.</p>
<p>In larger catchments and rural areas the story is more complicated than in cities. If the soil is very wet as a result of rain over the previous weeks and months, then when a big storm hits there will be a lot of runoff. In contrast, if the soil is dry then flooding is less likely to be a problem. </p>
<p>Engineers currently use simple models to estimate this relationship between soil wetness and storm rainfall. But our research indicates that these simple models will need to be replaced with longer-term simulations that model all of the previous rainfall leading up to the storm. </p>
<p>Simple models use simple assumptions to translate rainfall risk into flood risk. But if these assumptions are incorrect, our estimates of flood risk (that is, the probability of a given flood magnitude occurring in any particular year) could be wrong. Flood risk is used to guide infrastructure assessment through cost-benefit ratios, so getting it right is important.</p>
<p>One of the reasons that catchment wetness varies is because of climate cycles like El Niño and La Niña. We have some idea how these and <a href="https://theconversation.com/droughts-and-flooding-rains-it-takes-three-oceans-to-explain-australias-wild-21st-century-weather-56264">similar ocean cycles</a> affect our climate, including the fact that they can cause <a href="http://onlinelibrary.wiley.com/doi/10.1029/2002GL015992/abstract">fluctations in flood risk over decades-long timescales</a>. </p>
<p>The difficulty here is that for most locations we only have 50 to 60 years of recorded river flow data. This makes it hard to separate out the influences of these climate cycles from other trends in flood data, such as the effect of increasing urbanisation. </p>
<p>There has been progressively less monitoring of streamflow in Australia <a href="http://www.tandfonline.com/doi/abs/10.1080/13241583.2007.11465329">over the past few decades</a>, and this makes it even harder to understand regional changes in flood risk. Governments need to prioritise investment in data collection to allow us to improve our estimates of the risk of flooding and the associated damages now and in the future. </p>
<p>The recent work by the Bureau of Meteorology to develop a comprehensive set of high quality streamflow gauge <a href="http://www.bom.gov.au/water/hrs/">data</a> is a step in the right direction, but much more investment is needed in these areas.</p>
<p>Finally, we recommend that continued research into the fundamental changes likely from climate change is required. This requires climate models to be run at a range of resolutions to enable all the important climate processes for extreme rainfall to be properly represented. </p>
<p>Recent pressure on CSIRO’s climate modelling capabilities is concerning – the scientific questions are by no means fully answered on these topics. It is great to see the <a href="http://rses.anu.edu.au/news-events/new-arc-centre-excellence-climate-extremes">recent funding of the ARC Centre of Excellence on Climate Extremes</a>. The work of these researchers, combined with ongoing efforts across Australia, will be important to provide better assessments on climate changes. This can help engineers and hydrologists continue to provide accurate flood risk estimates.</p><img src="https://counter.theconversation.com/content/68170/count.gif" alt="The Conversation" width="1" height="1" />
<p class="fine-print"><em><span>Fiona Johnson receives funding from the Australian Research Council and World Health Organisation. </span></em></p><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>Seth Westra receives funding from the Australian Research Council and various State Government research funding programs. </span></em></p>Floods are a costly part of Australian life, which means we need to get better at predicting exactly when - and how severely - they are likely to strike in the future.Fiona Johnson, Senior Lecturer, School of Civil and Environmental Engineering, UNSW SydneyChristopher J White, Lecturer in Environmental Engineering, University of TasmaniaSeth Westra, Associate Professor, School of Civil, Environmental and Mining Engineering, University of AdelaideLicensed as Creative Commons – attribution, no derivatives.