Trends in the intensity and frequency of heavy rainfall in tropical Australia and links with the Southern Oscillation

Daily rainfall data for 53 stations in the Australian tropics have been used to investigate interannual changes in the intensity of the 90th and 95th percentiles and the frequency of events exceeding a long-term average of the 90th and 95th percentiles. The analysis considers rainfall in the months between September and April from 1910 to 1989. Increasing trends in the 90th and 95th percentile rainfall intensity and frequency occur at most stations, but few are statistically significant. Some stations with negative trends are located south of the Gulf of Carpentaria. Strong positive correlations exist between total summer half-year rainfall and both the intensity and frequency of heavy rainfall. Relationships between the Southern Oscillation Index (SOI) and these heavy rain-fall parameters were stronger during the period from 1950-1989 relative to 1910-1949, suggesting a change in large-scale atmospheric circulation patterns. In eastern tropical Australia, the winter SOI is well correlated with heavy rainfall parameters in the summer half-year, so there is potential to foreshadow heavy rainfall events two seasons in advance.