IMPLICATIONS OF CLIMATE-CHANGE DUE TO THE ENHANCED GREENHOUSE-EFFECT ON FLOODS AND DROUGHTS IN AUSTRALIA

Potential impacts of climate change on heavy rainfall events and flood ing in the Australian region are explored using the results of a gener al circulation model (GCM) run in an equilibrium enhanced greenhouse e xperiment. In the doubled CO, simulation, the model simulates an incre ase in the frequency of high-rainfall events and a decrease in the fre quency of low-rainfall events. This result applies over most of Austra lia, is statistically more significant than simulated changes in total rainfall, and is supported by theoretical considerations. We show tha t this result implies decreased return periods for heavy rainfall even ts. The further implication is that flooding could increase, although we discuss here the many difficulties associated with assessing in qua ntitative terms the significance of the modelling results for the real world. The second part of the paper assesses the implications of clim ate change for drought occurrence in Australia. This is undertaken usi ng an off-line soil water balance model driven by observed time series of rainfall and potential evaporation to determine the sensitivity of the soil water regime to changes in rainfall and temperature, and hen ce potential evaporation. Potential impacts are assessed at nine sites , representing a range of climate regimes and possible climate futures , by linking this sensitivity analysis with scenarios of regional clim ate change, derived from analysis of enhanced greenhouse experiment re sults from five GCMs. Results indicate that significant drying may be limited to the south of Australia. However, because the direction of c hange in terms of the soil water regime is uncertain at all sites and for all seasons, there is no basis for statements about how drought po tential may change.