The impact of climate change on hailstorms in southeastern Australia

Abstract

Data from a number of locations around southeastern Australia were analysed to determine the influence of climate change on the frequency and intensity of hail events in this region. The relationship between Convective Available Potential Energy (CAPE), frequently used as a measure of atmospheric instability, and hailstorms was investigated using both NCEP/NCAR reanalysis data (a data set comprising a blend of observations and model simulations) and also direct sounding data obtained from the Australian National Climate Centre. Two locations were chosen in southeastern Australia, Mount Gambier and Melbourne, over the months August to October for the period 1980–2001. A statistically significant relationship between hail incidence and CAPE values was established for both NCEP/NCAR and sounding data at both study sites. A stronger relationship was found between hail incidence and the CAPE, which was calculated using NCEP/NCAR data, than that between hail and the CAPE from the actual sounding data. A similar analysis was also conducted at both sites using the totals–totals index (TT index), which is an alternative measure of atmospheric instability. The CSIRO Mk3 Climate System Model was used to simulate values of CAPE for Mount Gambier in an environment containing double the pre-industrial concentrations of equivalent CO2. The results showed a significant decrease in CAPE values in the future. From this, assuming the relationship between CAPE and hail remains unchanged under enhanced greenhouse conditions, it is possible that there will be a decrease in the frequency of hail in southeastern Australia if current rates of CO2 emission are sustained. The severity of future hail events was investigated using crop-loss data from insurance companies. Strongest correlations were found between the crop-loss ratio (value of crop lost to hail damage over the total insured value of crop) and the number of days in a crop season with a TT index greater than 55. Results from the CSIRO Mk3 Climate System Model revealed that there was no significant difference between the number of days with a TT index over 55 for the simulation using current CO2 levels and that based on doubled equivalent pre-industrial CO2 concentrations (roughly equivalent to 2050 in the chosen emissions scenario). This implies that, for southeastern Australia, crop losses due to hail damage would not significantly increase under enhanced greenhouse conditions. Copyright © 2005 Royal Meteorological Society.