The Hydrological Impacts of Climate Change and Variability in the

ii There is growing evidence that the Earth’s climate is changing as a result of natural variability and the enhanced greenhouse effect. This may have serious implications for water resources at a regional scale. In the South West of Western Australia alterations in the rainfall pattern have been observed, with noticeable consequences for runoff and streamflow. This study aimed to quantify how rainfall patterns have changed in the Murray Hotham Catchment in the Peel-Harvey sub-region during the last century, and how the catchment has responded hydrologically to this change. It also aimed to investigate how projected future change in climate characteristics may influence catchment hydrological processes. Rainfall and streamflow data were compared from pre-1975 to post-1975, when a step change has been observed in other parts of the South West. A 10 % to 17 % reduction in mean annual rainfall was observed, with less very wet years occurring after 1975. This was accompanied by a seasonal shift in rainfall, with a large decrease in autumn and early winter rains, and a much smaller increase in spring and summer rains. No clear trend was observe