Heat

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GUEST OBSERVATION
Melbourne and Adelaide have been most prone to deadly heatwave conditions among Australia’s five largest cities, according to my new research published in Climatic Change.
My study shows that between 2001 and 2015, Melbourne and Adelaide suffered the most exposure to temperatures beyond a crucial threshold of 7.26℃ above the average. Above this threshold, deaths are more likely because people are not acclimatised to the extreme weather.
I estimated that there were 151 deaths in Melbourne and 144 in Adelaide due to extreme heatwaves - those above this 7.26℃ threshold - between 2001 and 2015.
Heatwaves can cause significant numbers of deaths, especially among vulnerable groups of people who are not prepared for or acclimatised to extreme hot temperatures.
Even though Melbourne and Adelaide are located in more temperate areas (in comparison with more northerly cities such as Brisbane), they have been periodically hit by severe heatwaves.
In my research, I looked at the “Excess Heat Factor”, a measure used by the Bureau of Meteorology as part of its heatwave forecasts. It is the difference between the 3-day average temperature and the 30-day average, and is therefore a measure of how “unusually hot” it is during a heatwave. It captures how much residents are likely to struggle to cope with the heat.
The graphs below show the frequency of excessively hot or cold weather for each of Australia’s major cities from 2001 to 2015. These charts show that most days had temperatures where the 3-day average was 2℃ higher or lower than the 30-day average.
A grey dashed line shows the extreme heat threshold that my study found was associated with higher deaths, relative to moderately warm and cool days. I then estimated the threshold at which there is a significantly increased risk of deaths.
The death rate (per 100,000 people) that coincides with the extreme heat acclimatisation measure is shown as a black line on each of the graphs. This is an average impact of temperature on death rates, adjusted for different cities’ population sizes and baseline death rates.
Between 2001 and 2015, most of the events above the 7.26℃ extreme heat threshold occurred in Adelaide, Melbourne and Perth. Brisbane and Sydney had fewer days above this threshold.
<img src="https://images.theconversation.com/files/230324/original/file-20180802-136673-gj66go.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt=""><img src="https://images.theconversation.com/files/230323/original/file-20180802-136652-2vfjgm.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt=""><img src="https://images.theconversation.com/files/230322/original/file-20180802-136667-1set3o3.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt=""><img src="https://images.theconversation.com/files/230326/original/file-20180802-136667-1xm8n3r.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt=""><img src="https://images.theconversation.com/files/230325/original/file-20180802-136670-r1mg15.png?ixlib=rb-1.1.0&amp;q=45&amp;auto=format&amp;w=754&amp;fit=clip" alt="">
 Figure 1 – Histograms of the Excess Heat Index for major Australian cities between 2001 and 2015.
The importance of acclimatisation
Several previous studies have linked excessive heat to adverse events such as deaths (see here, here and here), and emergency department visits and ambulance call-outs (see here, here and here). But my study is the first to solely focus on the extreme heat index acclimatisation measure, and to identify a temperature threshold in this way. This measure is important, as it identifies the times when residents of cities with different background climates begin to struggle with the heat.
The Bureau of Meteorology does not currently use the 7.26℃ threshold identified in my paper. Doing so may improve predictions of which heatwaves are most likely to turn deadly for significant numbers of people living in our major cities.
Implications for policy
Since the severe heatwaves of 2009, many states and territories have implemented or revised their heatwave response plans, or conducted awareness campaigns to educate people about the health risks. But more can be done to make vulnerable people aware of upcoming heatwave events.
A 2016 review proposed that heatwave response plans and early warning systems should be evaluated and updated at least every five years, to ensure that they remain effective, and to incorporate up-to-date knowledge about population-level vulnerability to heat stress.
While my research has focused on Australia’s five largest cities, this does not mean that extreme heat is any less dangerous in other areas. Nor is the danger limited to prolonged heatwaves – individual hot days can catch people out too. A NSW study found that emergency hospital admissions due to dehydration and other heat-related injuries rose significantly on individual hot days, as well as during hot spells lasting at least three days.
This suggests that we need to develop more complex heat risk management plans, with targeted responses for different health issues based on the longevity of extreme heat events.
Implications for the future
We also need to consider the patterns of extremely hot temperatures that we are likely to encounter in the future. Recent research found that changes in the frequency and duration of heatwaves will be larger in the north of Australia than the south. But the same study also found that “heatwave amplitude” – the intensity of the hottest day of the hottest heatwave – will increase more in southern parts of Australia.

This research suggests that cities south of Brisbane will experience the most severe temperature spikes beyond what their residents are used to dealing with.
Thomas Longden, Senior Research Fellow, University of Technology Sydney
This article was originally published on <a href="http://theconversation.com" target="_blank">The Conversation</a>. Read the <a href="https://theconversation.com/melbourne-and-adelaide-have-been-australias-most-vulnerable-major-cities-to-killer-heatwaves-100950" target="_blank">original article</a>.
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j.ballantyne1990-6AQqhLzZaK

Melbourne and Adelaide have been Australia’s most vulnerable major cities to killer heatwaves

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Disadvantaged Australian suburbs risk having hotspots more than 10 degrees higher than those in greener more affluent areas, according to a study from RMIT.
The report, titled Where Should All the Trees Go is produced with CSIRO Data 61 and the University of Western Australia. The study examined greenness levels across Australia’s metropolitan areas and how 139 local governments are performing in their greening plans.
Lead author, Associate Professor Marco Amati from the RMIT Centre for Urban Research, said greening efforts of local governments had not been as effective as hoped.
“Governments keep track of the green cover in cities as this has implications for adaptability in extreme weather events, biodiversity, and is linked to the community’s overall wellbeing,” he said.
“Using i-Tree – a method for sampling urban vegetation distributions and land covers – we found there has been a major decline in canopy coverage.
“As they lose vegetation, urban areas start to act like heat sponges.
“Our study showed areas identified as less affluent are at risk of having urban hotspots that are more than 10 degrees higher than those found in wealthier areas.
"To identify which areas of socioeconomic and health disadvantage also coincide with a lack of green cover and a high incidence of heat, the team developed a new Vulnerability to Heat, poor Health, Economic Disadvantage and Access (VHHEDA) index.
“Using this index, we found that green spaces and heat concentration in Australia are spread unevenly, which is contributing to an uneven spread of economic and health circumstances."
The research found Australian metropolitan areas have experienced a loss of vegetation equivalent to the size of Brisbane in the last three years, risking heat spikes particularly in less affluent areas.
Report co-author Dr Bryan Boruff from the University of Western Australia said urban vegetation losses and gains can often be explained by the changing nature of neighbourhoods across the country.
“Local governments showing the greatest green space losses across Perth lie in a band that stretches from inland Melville to coastal East Fremantle where the traditional Aussie backyard is losing ground to densification and infill,” he said.
“While it is known that the Australian backyard is disappearing, much more research is required to understand the factors influencing this unanticipated trend to help get our urban greening back on track.”
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