Southwest Western Australian winter rainfall and its association with Indian Ocean climate variability

Southwest Western Australia (SWWA) has experienced a significant decrease i n winter rainfall since the late 1960s. This decrease is unexplained and th e resultant problem of reduced water storage has been compounded by the lac k of any useful predictive skill at the seasonal time scale. This study use s recent gridded, historical data and simple linear correlation in order to evaluate the importance of links between rainfall and both mean sea level pressure (MSLP) and sea-surface temperature (SST) patterns over the Indian Ocean. The decrease in rainfall is linked to decreases in the density of low-press ure systems in the region and to increases in both MSLP and SST over the so uthern Indian Ocean. Warmer SSTs and increases in MSLP are associated with the observed long-term changes, but changes in these variables do not expla in a great deal of the observed interannual variability. Greenhouse-induced climate change is not regarded as a likely explanation f or the observed decrease, however, the existence of links with both MSLP an d SSTs suggests the existence of coupled air-sea interactions over the sout hern Indian Ocean which may be relevant at decadal or multi-decadal timesca les. A major difficulty with defining any such processes is the relative sp arseness of data at high latitudes in the Southern Hemisphere. This should be partly alleviated as more recent high quality data becomes available ove r time. Copyright (C) 2000 Royal Meteorological Society.