The University of New South Wales has carried out a continental-scale analysis of changes in hail hazard in Australia - a leading cause of insured losses in Australia.
The data shows that from 1979–2021 annual hail-prone days decreased over much of Australia but increased in some heavily populated areas. For example, the annual number of hail-prone days increased by 40% around Sydney and Perth.
Changes in atmospheric instability have driven the trends. This study shows demonstrates substantial increases in hail frequency in major Australian cities where hail impacts are most significant.
The Australian cities of Sydney, Brisbane and Canberra have all been affected by billion-dollar hailstorm events, and from 2014 to 2021, the seven most costly hailstorms in Australia caused a total of AUD $7.4b in insured losses.
There are, globally, three main expected effects of anthropogenic climate change on hailstorms. First, atmospheric instability is expected to increase owing to increased saturation deficit in a warmer atmosphere affecting storm initiation and leading to stronger updraughts that can produce larger hailstones.
Second, the melting-level height of hail, at which the wet-bulb temperature is 0 °C, is higher in a warmer atmosphere A higher melting-level height implies more melting of falling hailstones and allows only the larger hailstones to survive, eliminating surface hail or increasing the mean hailstone size.
Third, overall vertical wind shear is expected to decrease. A decrease in wind shear would normally be expected to reduce hailstorm intensity but the situation is complicated because local changes in wind shear may differ at times when hailstorms occur. Combining these offsetting factors, the broad expectation is that under climate change, surface hail may become less frequent due to increased melt but more severe owing to increased hailstone size at the ground. However, observations and simulated projections show that this expectation does not hold everywhere, with strong geographical inhomogeneity in climate responses and the resulting effects on hailstorms.
Projections exploring responses to global temperature increases show increases in severe-storm-favourable conditions for most of Australia, with statistically significant trends, particularly in the northwest and southeast under larger (2–3 °C) temperature increases.
If you are a weather geek you can read the full report here.