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Hail to be more frequent in Australia, more severe worldwide

An international review led by a Sydney-based academic predicts hail severity will increase in most regions of the world while Australia will more frequently experience hailstorms.

An unstable atmosphere caused by climate change threatens to bring more extreme hail events to Australia’s largest city.

“The hail threat is likely to increase in Australia, especially in Australia’s south-east including the Sydney area,” researcher at the UNSW Sydney’s Climate Change Research Centre Tim Raupach said.

The study, published in Nature Reviews Earth & Environment, found the effects of climate change on hailstorms are likely to vary markedly by region, with a general expectation that hailstorm frequency will increase in Australia and Europe and decrease in East Asia and North America, while hailstorm severity will increase in most regions.

The atmospheric influences on hail – an unstable atmosphere, the amount of melting of falling hailstones and wind shear or differences in wind by height – were examined in light of a warming climate.

“We know with climate change that we are going to have more moisture in the atmosphere and that leads to more instability in the atmosphere, so we expect there will be more tendency for thunderstorms to occur,” Dr Raupach said.

Hail will be less frequent in many regions because the melting level – the height in the atmosphere below which ice begins to melt – will get higher, so hail that forms high in the atmosphere has more time to melt as it falls and “may indeed melt entirely before it gets to the ground, and you end up with no hail at the surface,” Dr Raupach says.

"There’s more melting essentially in the future,” Dr Raupach said.

However, greater instability in the atmosphere is set to lead to the formation of much larger hailstones.

“When the hail does survive this extra melting, it will be larger and more severe when it does actually hit the surface,” Dr Raupach says.

Wind shear – a process that “organises” storms and makes them more severe – is expected to decrease, he said, but hail storms will be more affected by the other two factors.

Hailstorms are dangerous and costly phenomena. Severe hail on October 31 which struck areas of Brisbane, the Gold Coast and the Sunshine Coast has produced more than 33,500 insurance claims so far, with losses estimated at $805 million, the Insurance Council of Australia says.

Researchers from University of Bern, Central Michigan University, Karlsruhe Institute of Technology, University of Illinois, Colorado State University and Peking University took part in the study.