Streamflow decline in southwestern Australia, 1950-2008

Abstract

Southwest Western Australia (SWWA) has experienced a 15-20% reduction in rainfall since the 1970s with severe reductions in inflows to Perth drinking water reservoirs. To quantify rainfall and runoff patterns, we used trend and change point analyses for a 50 year record (1950-2008) and in the last two decades (1989-2008). From 1950-2008, trend tests showed significant declines in annual rainfall and runoff with corresponding change points for both rainfall and flow in the late 1960s or mid-1970s. In the more recent record (1989-2008), runoff declined in the majority of catchments, but rainfall did not show a significant downward trend. Rather, streamflow decline was observed as a step change in response to the occurrence of below-average rainfall years. A shift from perennial to ephemeral streams and a decline in the runoff coefficient (runoff/rainfall) in the last decade suggests a new hydrologic regime has developed with important implications for future surface water supply. Copyright © 2010 by the American Geophysical Union.