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Flash-flood threat growing faster than feared

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Rises in hourly rainfall during intense storms have exceeded climate scientists’ expectations, heightening the risks of flash flooding and increased insurance claims.

A study of Australian rainfall data over the past 50 years finds rates of increase in short storms are up to three times expectations in the tropical north, and about double those for most of the rest of the country.

The University of Adelaide’s Seth Westra, co-author of research published in Nature Climate Change, says the findings have implications for urban planning and infrastructure that was built to cope with more benign conditions.

“It is very much a multi-pronged problem,” he told insuranceNEWS.com.au.

“It affects the insurance industry, certainly, and it affects governments at all levels and civil engineers who are responsible for designing the infrastructure.”

Rises in daily rainfall are more consistent with expectations, but predictions for hourly change represent a “severe underestimate”.

“Why that is occurring and whether that is going to continue to occur is something we don’t know at this stage,” Dr Westra said.

Climate scientists have said rainfall will increase by about 7% for each degree of global warming, but the study of Bureau of Meteorology data for the tropical north finds 20% increases during hourly storms. Other regions show gains of 14-15%.

The higher-intensity falls could be further powered by increased global warming.

“Then you are talking about a fairly significant percentage change in those rainfall events and therefore cascading implications for flood risks,” Dr Westra said.

Insurance Council of Australia GM Risk Karl Sullivan says many underwriters recognise rainfall-intensity impacts through pricing based on increasing claims.

Besides addressing the root causes of climate change, strategies to reduce risk should include keeping buildings well maintained, improving defensive infrastructure and enhancing the resilience of future developments, he says.

“Towns that have well-functioning drainage and levee systems fare better in these events and experience fewer insurance claims and lower premiums,” he says on his LinkedIn page.