Hail Climatologies for Sydney and Brisbane, Australia, Derived from Single-Polarization Radar and Insurance Claim Data

Severe hail storms represent a major hazard along the central east coast of Australia, with previous events causing billions of dollars’ worth of damage. Knowledge of the spatial distribution of these storms is thus relevant both to forecasters and the insurance industry. Here, the hail hazard in the vicinity of the major cities of Sydney and Brisbane is quantified for a six-year period using observations from S-band single-polarization radars. Three-dimensional reflectivity mosaics with 1 km spatial resolution and 5 min temporal resolution are constructed for each domain and used to derive daily gridded fields of the maximum estimated size of hail (MESH). Using home insurance claim data as ground truth for hail damage, an optimal MESH threshold separating damaging and non-damaging hail is identified. The climatologies of these two categories of hail are then analysed.

We find the spatial distribution of hail (both damaging and non-damaging) to be much more concentrated in the Brisbane domain, with a pronounced maximum located to the southwest of the city. This fits with operational experience and previous research which indicate that topographically driven circulations (in particular the sea breeze) are a major factor in severe storm development in this region. In contrast, aside from an expected land–sea gradient, hail distribution around Sydney is quite homogeneous, suggesting that forcing for severe storm is dominated by surface heating and the large-scale flow.