Relationship between radar-derived hail kinetic energy and damage to insured buildings for severe hailstorms in Eastern Australia

Hailstorms are by far the costliest insured natural hazard in Australia. Major metropolitan areas such as Sydney and Brisbane, located in mid-latitude coastal Eastern Australia, are especially vulnerable due to building exposure and geographical location. Results are presented using data from metropolitan Sydney and Brisbane for seven recent severe storms, including the April 1999 Sydney hailstorm. cus of this study is on comparisons between the radar-derived pattern of hail kinetic energy and damage to residential buildings in the form of insurance claims. CAPPI (Constant Altitude Plan Position Indicators) reflectivities were generated from S-band radar at low storm levels (1.5 km) and the hail kinetic energy was calculated. High reflectivity hail cells (≥ 55 dBZ) were investigated during the time they passed over occupied urban areas causing damage on the ground to insured assets. The preferred area for hail damage was found to be located to the left side and towards the rear left flank with respect to the storm movement. Higher claim costs were identified within storms that produced “follow up cells.” mage variables were derived from insurance claims on a 2 × 2 km grid: average cost and spatial average loss ratio. The radar fields were shifted horizontally in order to maximise correlations between the damage on the ground and the radar signal aloft. Correlation coefficients improved on average from 0.09 before shift to 0.47 after optimal shift for average cost; corresponding values for spatial average loss ratio improved from 0.06 to 0.43. These improvements in correlation are gratifying, especially considering the limitations of the data. Nonetheless, our general conclusion, when looking at all storms, is that hail kinetic energy as calculated in this study cannot by itself provide a robust, consistent and reliable predictor of insured losses.