Assessment of model projections of climate-change induced extreme storms on the south-east coast of Australia

General circulation models (GCMs) and their downscaled regional-scale equivalents have been important tools for climate-change studies. However, there has been limited assessment of the performance of GCMs and downscaled models in simulating extreme storms in temperate coastal environments. This study assesses the model characterization of extreme storms on the heavily populated coast of south-east Australia. Twenty-year average recurrence interval (ARI) storm intensities derived from generalized extreme value (GEV) distributions based on observed and large-scale atmospheric model data are compared. Changes in extreme storms from past climate to a high-emission future scenario are also investigated. Simulations of storm minimum surface pressures compared favourably with measured data. Both the GCMs and downscaled models reproduced the observed decrease with increasing latitude along the coast in the 20 year ARI of minimum surface pressure. Both indicated that the minimum storm surface pressure should change negligibly in a high-emission future. Although the models underestimated the maximum daily precipitation significantly, models are improving significantly with CMIP epoch and downscaling. In the high-emission future scenario, the GCMs and NARCliM projected the 20 year ARI maximum daily precipitation would increase in the order of 25%. GCMs and the corresponding downscaled products presently do not represent the extreme value distributions of historical wind speed data well, overestimating at smaller values of ARI and significantly underestimating in larger values of ARI. Significant changes in the magnitude of the 20 year ARI maximum daily-average onshore wind speed are not projected for the high-emission future. This study quantitatively evaluates climate model projections of changes in regional extreme storms along the populous south-east Australian coast. For a high emission future, precipitation at the same recurrence interval is projected to increase significantly, yielding major increases in runoff and substantially larger floods. image