Towards better understanding of changes in rainfall-runoff relationships during the recent drought in south-eastern Australia

Abstract

It has been contended that during the 1997-2008 ‘Millennium’ drought there was an unexpectedly large decline in runoff from some catchments in south-eastern Australia (SEA). Potter et al. (2011) suggested that across 34 unregulated catchments in SEA the area weighted reduction in streamflow during the drought was 46 percent. Sixty-five percent of this was attributed to reduction in annual rainfall and 7 percent to the direct or indirect effect of changes in average annual maximum temperature. The remaining 28 percent was unexplained residual; potentially due to changes in seasonality and inter-annual variability of rainfall; and/or anthropogenic change (i.e. in particular farm dams), change in vegetation or a change in dominant hydrological behaviour. In this study we aim to develop a better understanding of why the reductions in runoff under the recent drought have been so large and why the unexpected residual as computed by Potter et al. varied spatially.