Influence of Indian Ocean sea surface temperature variability on southwest Western Australian winter rainfall

Southwest Western Australia (SWWA) has experienced a significant drop in winter rainfall during the past three decades, the cause of which is still subject to considerable speculation and debate. This prolonged drought has heavily impacted on water resources in the state, the predicted continuation of which is of major concern to the people of Western Australia. In this paper, the possible influence of sea surface temperature (SST) variability occurring over parts of the Indian Ocean on SWWA rainfall variability is explored. The results of our statistical analyses show that winter rainfall (May to October) in SWWA is lower in years when warm SSTs dominate the southern and tropical western Indian Ocean, compared to years when cool anomalies are present in the same region. In addition, a step change that can be detected in the SST anomalies in the southern and tropical western Indian Ocean occurring around 1970 happens to coincide with a similar sharp reduction in SWWA rainfall. It is suggested that the possible association between the Indian Ocean SST anomalies and observed variability of SWWA rainfall may be utilized, at a minimum, as possible diagnostic tools in the evaluation of global climate model outputs, in this way constraining the uncertainties in their predictions.