New research from UNSW shows climate change could cause hailstorms to get worse in some of Australia' s most densely populated cities.
Climate change might cause hailstorms to become more damaging in some Australian cities, a study on future hail trends published today has found. This includes the capital cities of Sydney, Canberra, Melbourne and Perth.
In analysing simulations of weather in a warmer world, "we're seeing an increase in hail size over some capital cities", says lead author Dr Tim Raupach from UNSW Sydney's Institute for Climate Risk and Response.
"Our projections also show hailstorms becoming more frequent in Brisbane, Sydney, and Canberra," he says.
Yet, Dr Raupach says, while projections are helpful, there's still a lot we don't know. For some cities, like Adelaide, the simulations don't show major changes.
"More research is needed to better address the complexities in modelling hail."
Bigger stones, more often
From smashed windscreens in Sydney to ruined crops in Queensland, hail is one of nature's most dramatic - and costly - displays.
Hailstorms were responsible for more than 20% of insured losses in Australia from 1967 to 2023.
The damage is largely driven by the size of hailstones - and the stones can get big. Australia's record near Mackay, Queensland was around 16 cm across - more than double the diameter of a cricket ball.
While massive hailstones like these are rare, they're not impossible. Dr Raupach says more intense storms in the future could increase the chances of large-diameter hail.
"We looked at changes in hailstone size between simulations of historical and future periods," he says.
"And we can see increases in hail size produced by the model around Sydney, Canberra, Melbourne and Perth.
"For example, in past simulations, very large, 10 cm hailstones were expected once every 20 years around Melbourne. But in a warmer future, it's once every three years."
What makes a hailstone?
Hailstorms rely on warmth to start, so usually occur in the spring and summer months, when warm air from the land or ocean is pushed up into cooler air and rises into the atmosphere.
"Hailstone size is controlled by how strong the updraft is in in a thunderstorm," Dr Raupach says.
In a thunderstorm, strong winds - updrafts - carry moisture high up into the atmosphere, where it freezes. These ice particles - known as 'hail embryos' - pick up supercooled water as they circulate through the storm cloud.
"The stronger the updraft, the longer a hailstone can stay in the storm and grow," says Dr Raupach.
"Eventually, the hailstone gets too heavy and falls."
To grow large hailstones, the storm cloud needs to be tall, with lots of energy to keep the stone suspended long enough to gather layers of ice.
The trajectory the hailstone follows within the storm also matters.
"There are regions inside a storm that have more moisture and are colder," says Dr Raupach.
"The more time the embryo spends in these moist, cold spots, the larger it can grow."
Rain, hail or shine?
While hail can fall anywhere in Australia, certain regions are particularly exposed.
"The main region is the East Coast from a bit north of Brisbane to a bit south of Sydney," Dr Raupach says.
However, other hotspots, like the remote goldfields of Western Australia and the Gulf of Carpentaria, also appear in radar records. These are sparsely populated areas where observational data and firsthand reports are more difficult to gather - which is why computer modelling is often used.
With Australia's solar industry booming, another emerging vulnerability is rooftop solar panels.
"Hail can damage solar panels. We've seen it happen - in Brisbane in 2020 and in the US as well," says Dr Raupach.
But, he says, this shouldn't deter any investment in renewables.
"We should also think about how to strengthen our cities to resist hail damage, especially if hailstone size is increasing with climate change."
We should also think about how to strengthen our cities to resist hail damage, especially if hailstone size is increasing with climate change.
Are Australians prepared?
The Australian Bureau of Meteorology issues hail warnings. And some insurance policies cover hail damage.
While insurance companies have long tracked hail risk, Dr Raupach works directly with the industry to help them understand current and future hazards.
However, physical preparedness within the community is another matter.
"To be protected from hail you can move undercover, move your car undercover, have good insurance and have strong roof tiles," Dr Raupach says.
He says some farmers use hail nets.
Dr Joanna Aldridge, co-author of the study from QBE Insurance, says a key issue remains.
"Australian building standards still don't include hail resilience, which leaves many properties vulnerable," Dr Aldridge says.
For now, Dr Raupach recommends insurance, preparedness and awareness. But in the long term, he sees two paths forward.
Firstly, he suggests reducing greenhouse gas emissions as a key step in mitigating the impacts of climate change on severe weather events.
"Reducing emissions of greenhouse gases remains a crucial objective," says Dr Raupach.
Secondly, he says research should continue. As an example, there is an emerging question of how much urban environments - the structures of cities - affect hail. He says there may be innovative options worth exploring for designing and redesigning future cities - a research question he and colleagues are working on.
"It's very early days, but maybe one day we could design cities with a reduced storm risk," Dr Raupach says.
For now, he says Australians living in hail-prone regions should stay alert - and perhaps reconsider where they park the car in a storm.
Disclosure statement: Timothy Raupach receives funding from QBE Insurance, Guy Carpenter, and the Australian Research Council.
