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Increasing Cost of Natural Hazards as Climate Changes

A study of Australian natural hazards paints a picture of increasing heatwaves and extreme bushfires as the century progresses, but there is much more uncertainty about the future of storms and rainfall.

The study, published in a special edition of Climatic Change, documents the historical record and projected change of seven natural hazards in Australia: flood, storms (including wind and hail), coastal extremes, drought, heatwaves, bushfires and frost.

“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 issue editor A/Prof Seth Westra 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. 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.

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

The issue aims to disentangle the effects of climate variability and change on hazards from other factors such as deforestation, increased urbanisation, people living in more vulnerable areas, and higher values of infrastructure. The studies found:

  • an increased occurrence in recent decades of extreme bushfires, 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;
  • heatwaves are Australia’s most deadly natural hazard, causing 55% of all natural disaster-related deaths. Increasing trends in heatwave intensity, frequency and duration are projected to continue throughout the 21st century; and
  • the costs of flooding have increased significantly in recent decades, but factors behind this increase include changes in reporting mechanisms, population, land use, infrastructure and extreme rainfall events. The physical size of floods has either not changed at all or even decreased in many parts of the country.