A hailstorm can undo a season’s work in minutes. It can strike quickly and unevenly, shredding wheat, bruising fruit, flattening crops – while also leaving neighbouring paddocks untouched.
In a new Nature Climate Change study, scientists from UNSW Sydney say the geography and seasonality of that risk is changing.
As the planet warms, the atmospheric conditions that produce damaging hail are projected to shift away from some warmer regions towards the cooler parts of the world – including south-eastern Australia and New Zealand.
Lead author Dr Tim Raupach from the UNSW Institute of Climate Risk and Response says this is part of an overall hail condition frequency shift towards the poles.
“Under modelling scenarios of 2°C and 3°C of global warming, we see this overall shift towards more risk in cooler places and cooler times of the year,” Dr Raupach says.
“So increasing risk in winter and often decreasing risk in summer – a shift from warmer to cooler regions and seasons,” he says. “Those cooler regions include not only parts of southern Australia and New Zealand, but northern North America and Europe.
“And there are decreases – though still with a lot of uncertainty – in the subtropics and parts of the mid-latitudes. This includes much of Australia as well as regions of India, China and much of Africa.”
An atmospheric tug of war
Because hailstorms are brief and difficult to observe, the researchers did not model hailstones directly. Instead, they used three different proxies, or methods, to detect atmospheric conditions that occur when hail is more likely to form.
These proxies did not always agree, particularly in the tropics, underscoring how difficult future hail risk remains to predict. The disagreement showed that with a warmer atmosphere, several forces act at the same time.
“Usually, as the atmosphere gets warmer, we expect it to have more energy, which could be turned into updrafts,” Dr Raupach says. Updrafts are a key feature of hailstorms.
“When you have these strong winds in the thunderstorms, they can support the growth of larger hailstones,” he says.
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