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 Australian 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 are applied to the calibrated rainfall-runoff model to study the sensitivity of runoff and soil moisture to potential changes in the climate. Second, results from five global climate model (GCM) enhanced greenhouse experiments are analysed to provide regional climate change scenarios to estimate the range of plausible changes in runoff and soil moisture by the years 2030 and 2070. The sensitivity analyses indicate that changes in rainfall are always amplified in runoff with the amplification factor for runoff being higher in drier catchments. The change in rainfall has little effect on the soil moisture in wet catchments but in drier catchments, the percentage change in soil moisture levels can be greater than the percentage change in rainfall. Compared to precipitation, temperature increases alone have negligible impacts on the runoff and soil moisture. The simulations using the GCM scenarios indicate increases in annual runoff of up to 25% by the year 2030 in the wet tropical catchments near the north-east coast of Australia. The GCMs do not agree in the direction of rainfall change in south-east Australia, and the simulations show runoff changes of up to +/-20% by 2030. For Tasmanian catchments, up to 10% increase in runoff is simulated whereas for catchments in the South Australian Gulf, up to 35% decrease in annual runoff is simulated for 2030. Near the western coast of Australia, the simulations show runoff changes of up to +/-50%. These results show the potential for climate change to bring about runoff modifications that may require a significant planning response. They are also indicative of the fact that hydrological impacts affecting water supply and flood studies may be important in considering the cost and benefits of potential climate change.