Understanding the Interannual Variability in Severe Hail Storms in Australia

Hailstorms are a leading cause of insured losses in Australia, damaging vehicles, buildings, and agriculture amongst other infrastructure. Individual hailstorms have caused damage bills exceeding AUD$1b, particularly in the densely populated cities of Brisbane and Sydney on Australia’s east coast. Despite hail’s high damage potential, the drivers of the large observed interannual variability in large-hail events in Australia remain highly uncertain.
Here, we use the radar product Maximum Expected Size of Hail (MESH) to investigate the drivers of interannual hail variability across Australia’s most hail-affected regions. We use a MESH threshold of 30 mm for hail occurrences. Various studies have mentioned that MESH is a good discriminator for hail occurrences and that a great proportion of hailstorms and hail reports are captured by a 30-mm MESH threshold. We examine how different drivers of variability such as the El Niño Southern Oscillation (ENSO), Southern Annular Mode (SAM), and Indian Ocean Dipole (IOD) affect large-hail occurrence in Australia. We focus on areas where hailstorms cause the greatest damage, to perform a robust analysis of year-to-year variations in large-hail occurrences.
We found a strong correlation between the ENSO 3.4 index and large hail occurrences in Australia, mainly around these major cities of Sydney and Brisbane. We will present the results of our analysis for the Australian east coast’s most impacted cities: Sydney, Brisbane, Melbourne, and Canberra. This includes analysis of the interannual variability and its connection to large-scale climate drivers, convective parameters, and future research needs.