Past and future changes to inflows into Perth (Western Australia) dams

Study regionThe city of Perth is located within the region referred to as south-west Western Australia (SWWA) defined as southwest of a line connecting 30° S, 115° E and 35° S, 120° E.Study focusSWWA has experienced a prolonged decline in rainfall since the early 1970s accompanied by serious reductions to inflows into the major storage systems. Consequent research questions include: What caused the decline in rainfall? Why have inflows decreased so dramatically? What can be expected over the coming decades? In this study, we consider these questions making use of recent observations and the latest generation of climate model results which attempt to simulate the effects of increased greenhouse gas concentrations.New hydrological insights for the region under studyRecent observations show a continuation of dry conditions and confirm that a significant change in the relationship between rainfall and inflows appears to have occurred. There is little evidence that increasing local temperatures alone can explain this changed relationship which possibly represents long-term physical changes (e.g. groundwater levels) to the catchments. There is a strong consensus amongst recent model results that rainfall will decline further by the end of the 21st century. While this confirms findings from studies of previous model results, for the purposes of better estimating future changes to inflows it may now be more important to understand the reasons for the changed rainfall/inflows relationship.