Temporal Variations in Seasonal Rainfalls in Southwestern Australia

Abstract

Trends and oscillations that have affected seasonal rainfalls in southwestern Australia since 1880 are revealed, and the most likely accompanying circulation changes are discussed. Results include a general increase of rainfall in early winter and a decrease in late winter, although in a small area around Hopetoun the trends have been reverse. The Southern Oscillation is correlated with winter rainfall in the region, and extremes of the SO are associated with more widespread rainfall anomalies. Methods of analysing time series for oscillations are described in detail. Quasi-biennial oscillations have affected the rainfalls of all four seasons; that of early winter has been less persistent than the others, but is probably related to the stratopsheric QBO. Some consequences concerning the past behavior of the latter are mentioned. A 4-year oscillation has affected late summer rainfall. It is concluded that rainfall patterns are useful in investigating past circulation changes, but their usefulness would be less in other regions with more complex influences.