Australia's Deadly Heatwaves Are Only Getting Worse

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Heatwaves are Australia's most deadly natural hazard, causing 55 per cent of all natural disaster related deaths. Now a new comprehensive study of Australian natural hazards reveals they are only going to become more intense - and happen more often.

The study documents the historical record and projected change of seven natural hazards in Australia: flood; storms (including wind and hail); coastal extremes; drought; heatwave; bushfire; and frost.

Historical information on the most extreme bushfires – so-called "mega fires" – suggests an increased occurrence in recent decades with strong potential for them to increase in frequency in the future.

Over the past decade major bushfires at the margins of Sydney, Canberra, and Melbourne have burnt more than a million hectares of forests and woodlands and resulted in the loss of more than 200 lives and 4000 homes.

"Temperature-related hazards, particularly heatwaves and bushfires, are increasing, and projections show a high level of agreement that we will continue to see these hazards become more extreme into the 21st century," says Associate Professor Seth Westra, Head of the Intelligent Water Decisions group at the University of Adelaide.

"Other hazards, particularly those related to storms and rainfall, are more ambiguous. Cyclones are projected to occur less frequently but when they do occur they may well be more intense," Associate Professor Westra said. "In terms of rainfall-induced floods we have conflicting lines of evidence with some analyses pointing to an increase into the future and others pointing to a decrease".

The costs of flooding have increased significantly in recent decades, but factors behind this increase include changes in reporting mechanisms, population, land-use, infrastructure as well as extreme rainfall events. The physical size of floods has either not changed at all, or even decreased in many parts of the country.

Associate Professor Westra says one thing that became very clear is how much all these hazards are interconnected. For example, drought leads to drying out of the land surface, which in turn can lead to increased risk of heat waves and bushfires - while also potentially leading to a decreased risk of flooding.

The importance of interlinkages between climate extremes was also revealed in a coastal study.

"On the open coast, rising sea levels are increasing the flooding and erosion of storm-induced high waves and storm surges," says CSIRO's Dr Kathleen McInnes, the lead author of the coastal extremes paper. "However, in estuaries where considerable infrastructure resides, rainfall runoff adds to the complexity of extremes."

"We need robust decision-making that considers the whole range of future scenarios and how our environment may evolve. The biggest risk from climate change is if we continue to plan as though there will be no change. One thing is certain: our environment will continue to change."