Climate change has led to significant changes in weather patterns across the globe. The continuous rise in sea levels, melting of ice caps, extreme heatwaves and floods have affected every country of the world. In Australia, one major concern is the increase in hailstorm damage. Hailstorms are already among the most costly natural disasters in the country. With global warming, the damage potential from hail is likely to grow in some cities.
This article explains how climate change is affecting hailstorms in Australia. It explains how hail is formed, why larger hailstones and strong winds matter, and what the latest scientific models say about future hail risks. This article is based on a recently published study by UNSW Changes in Hail Damage Potential in Major Australian Cities With Global Warming which used advanced weather models to simulate changes in hail conditions from past to future climate scenarios.
What is Hail and Why Does It Cause Damage?
According to NOAA, Hailstones are formed when raindrops are carried upward by thunderstorm updrafts into extremely cold areas of the atmosphere and freeze. Hailstones then grow by colliding with liquid water drops that freeze onto the hailstone’s surface. If the water freezes instantaneously when colliding with the hailstone, cloudy ice will form as air bubbles will be trapped in the newly formed ice. However, if the water freezes slowly, the air bubbles can escape and the new ice will be clear.
Large hailstones can break windows, dent cars, damage roofs, and harm crops. If hail comes with strong winds, the damage is much worse. Winds can throw hailstones at high speed into walls and glass surfaces, increasing the destruction.
According to the Insurance Council of Australia (ICA), hail caused over 20% of all insured weather losses in Australia from 1967 to 2023. The largest loss on record came from the Sydney hailstorm in April 1999, which caused over A$8.8 billion in today's value.
Why Climate Change Affects Hailstorms?
Global warming changes the energy and moisture levels in the atmosphere. This affects how storms grow. Scientists expect that stronger storms in a warmer climate may produce fewer hail events but with much larger hailstones.
This is because higher temperatures raise the freezing level in the atmosphere. Smaller hail melts before reaching the ground, but bigger hailstones may survive and hit the surface. At the same time, more heat and moisture can make storms more unstable, supporting stronger updrafts that create giant hailstones.
The Study: Using Weather Models to Simulate the Future
A 2025 study published by a team from UNSW Sydney and supported by QBE Insurance looked at how hail and wind conditions could change in Australia. Historical and Future simulations were carried out by researchers using the Advanced Research Weather Research and Forecasting model. Using these models provided an estimate of hailstone diameter at the surface.
Simulations were carried out for two time periods, historical climate (1989-2009) and future climate (2080-2100) under a scenario where global temperature rises by about 2.4°C. For each season, simulations were run and from each simulation, only data from October 1 to February 28 were analyzed, since this period covers Australia’s main convective (hail-producing) season. The first 14-16 hours of each run were discarded to allow the model to “spin up” and stabilize.
The model produced hourly data and predicted the size of hailstones using a tool called HAILCAST. While most variables gave values at each hour, HAILCAST provided the maximum hail size within each hour. HAILCAST ran at every model time step, typically every 100 seconds, but sometimes more frequently (every 80 or 60 seconds) on days with unstable weather conditions.
To focus on realistic hail events, researchers only analyzed data from times and places where surface hail was predicted. Wind speeds (measured at 10 meters above ground) and thunderstorm characteristics were recorded for the same periods.
The model was driven by bias-corrected climate data, combining historical weather observations from ERA5 with future climate projections from the CMIP6 models under the SSP2-4.5 pathway. This approach assumes a moderate emissions future, where global mean temperature rises by 2.42°C between the historical and future periods.
To keep results accurate, any predicted hail larger than 18 cm in diameter (which is unrealistic and exceeds Australia's record of 16 cm) was excluded, especially where the model incorrectly predicted large hail over oceans. Less than 0.006% of land-based hail values were removed this way.
This rigorous setup allowed researchers to compare how hailstorm frequency, size, and wind speeds might evolve in Australian cities as the climate warms.
The study focused on Australia's major hail-prone cities mainly Sydney, Canberra, Melbourne, Brisbane, Perth, Adelaide, and Kalgoorlie. These areas cover about 65% of Australia's population.
What key trends did the study identify regarding hailstorms in Australia?
The research found that hailstorm frequency and size are likely to increase in some regions. Sydney/Canberra and Brisbane may see more frequent hail days. Melbourne, Perth, and Kalgoorlie may experience larger hailstones.
- Hail days increased: The number of days with hail went up by 29% in Sydney/Canberra and 15% in Brisbane.
- Larger hail: Maximum hail sizes increased by 7.8 mm in Melbourne and 3.9 mm in Sydney/Canberra.
- Return periods dropped: In Melbourne, 100 mm hail, which used to occur once every 20 years, may happen every 3 years.
The study also used "extreme value analysis" to understand how often the most severe hail and wind events might occur. It showed a higher risk of very large hailstones but fewer days with extremely damaging wind gusts.
Around Melbourne, the probability of a hail day producing giant hail more than doubled to 24%, and 100 mm hail was more than six times more likely in the future," the study reports.
Why Wind Still Matters?
Although strong winds are expected to decrease on hail days in cities like Melbourne and Sydney, average wind speeds around hailstorms may still rise. Strong winds matter because they make hailstones more dangerous. They push them sideways into buildings and windows, causing more damage. Even with fewer damaging wind gusts, the combination of high average wind speed and larger hail may still raise risks.
How is the Atmosphere changing?
The study also looked at how the atmosphere changes between the two time periods.
- Convective Available Potential Energy (CAPE): This measure of storm energy increased in cities like Adelaide, Brisbane, Melbourne, and Sydney/Canberra. More energy means stronger storms.
- Freezing Level Height: This rose in all cities. A higher freezing level means hail must grow larger to survive melting before hitting the ground.
- Wind Shear: There were only small changes in vertical wind shear. This means instability, rather than wind changes, is the main reason for stronger hailstorms.
What does this mean for Australia?
Cities like Sydney, Melbourne, and Brisbane are already at high risk from hail. This risk is expected to grow. Insurance companies and governments must consider the plans on how to prepare for larger hails and more frequent hailstorms. The study also shows that planners and designers need to upgrade to better building codes. While current codes in Australia do include wind protection but they do not include hail protection. As hail risks grow, this gap could lead to greater damage in the future.
There are a few things to keep in mind. The simulations used hourly wind data, which might underestimate the strongest gusts. This study has limitations as only the main storm for the season was studied for October to February, but hail can happen outside this window.
The study also used a single climate model. More research with model ensembles would help confirm these findings. Still, the results provide useful guidance for understanding future risks. Larger hailstones and more frequent hail events are expected in Sydney, Canberra, Brisbane, and Melbourne. Even if damaging wind gusts decline, higher average winds and giant hailstones will still raise the danger.
As weather patterns shift, Australia will need better planning, stronger building designs, and updated insurance models to reduce future losses. This research is a step forward in understanding how a warming world can change local storm risk.