Radar‐based Climatology of Damaging Hailstorms in Brisbane and Sydney, Australia

Severe hailstorms represent some of Australia's most costly natural disasters. In particular, the densely populated east-coast cities of Brisbane and Sydney have both been impacted by events that individually produced over AU$1 billion in insured losses. In this study, the frequency of damaging hailstorms in these regions is assessed over an eight-year period using single-polarisation radar observations. Reflectivity data from multiple radars are carefully calibrated and merged to produce daily grids of MESH (the maximum expected size of hail) at 1 km spatial resolution. Neighbourhood contingency tables are then used to define an optimal MESH threshold for identifying damaging hail events. This analysis makes use of a unique insurance dataset, comprising building-scale exposure and claim data over a multi-year period. Overall, damaging hailstorms occur on an average of 26 and 32 days per year in the Brisbane and Sydney regions, respectively. The actual cities of Brisbane and Sydney both experience about five damaging hailstorms annually. In both regions, the highest hail frequencies occur along the coastal slopes of the Great Dividing Range, with more localised maxima highlighting the potential role of mesoscale circulations in storm initiation and intensification. For Brisbane, the seasonal cycle shows a pronounced peak in December, while in Sydney hail frequencies are high throughout the warm season (November-March). This difference reflects the distinct seasonal cycles of convective instability in the two regions. Consistent with previous studies, the combination of CAPE and deep-layer shear is found to provide reasonable discrimination of environments conducive to severe hailstorms.