SIMULATION OF THE IMPACTS OF CLIMATE-CHANGE ON RUNOFF AND SOIL-MOISTURE IN AUSTRALIAN CATCHMENTS

The impacts of climate change on runoff and soil moisture in 28 Austra lian catchments are simulated using a hydrologic daily rainfall-runoff model. Two methods are used to provide the climate change scenarios. First, a range of arbitrary changes in temperature and precipitation a re applied to the calibrated rainfall-runoff model to study the sensit ivity of runoff and soil moisture to potential changes in the climate. Second, results from five global climate model (GCM) enhanced greenho use experiments are analysed to provide regional climate change scenar ios to estimate the range of plausible changes in runoff and soil mois ture by the years 2030 and 2070. The sensitivity analyses indicate tha t changes in rainfall are always amplified in runoff with the amplific ation factor for runoff being higher in drier catchments. The change i n rainfall has little effect on the soil moisture in wet catchments bu t in drier catchments, the percentage change in soil moisture levels c an be greater than the percentage change in rainfall. Compared to prec ipitation, temperature increases alone have negligible impacts on the runoff and soil moisture. The simulations using the GCM scenarios indi cate increases in annual runoff of up to 25% by the year 2030 in the w et tropical catchments near the north-east coast of Australia. The GCM s do not agree in the direction of rainfall change in south-east Austr alia, and the simulations show runoff changes of up to +/-20% by 2030. For Tasmanian catchments, up to 10% increase in runoff is simulated w hereas for catchments in the South Australian Gulf, up to 35% decrease in annual runoff is simulated for 2030. Near the western coast of Aus tralia, the simulations show runoff changes of up to +/-50%. These res ults show the potential for climate change to bring about runoff modif ications that may require a significant planning response. They are al so indicative of the fact that hydrological impacts affecting water su pply and flood studies may be important in considering the cost and be nefits of potential climate change.