Australian rainfall changes, 1910-1995

Annual and seasonal trends in heavy daily rainfall, total rainfall and the number of rain days were calculated for the whole of Australia and each State/Territory from 1910 to 1995, using high-quality daily data from 379 stations. Trend significance was determined using the Kendall-tau test and trend magnitudes were computed from linear regression. While many statistically significant trends were found, non-significant trends judged to be of special interest are noted. From 1910-1995, annual total rainfall has undergone secular changes with a significant 14 percent increase in Victoria and non-significant increases of 15-18 percent in New South Wales (NSW), the Northern Territory (Nt) and South Australia (SA). When analysed seasonally, non-significant changes of 10-40 percent were found in some States. Heavy rainfall indices were defined as the 99th and 95th percentiles (the highest and 5th highest daily amounts, respectively, in each three-month season). Australian areal-mean heavy rainfall has not changed significantly in any season. However, on a regional basis significant increases in heavy rainfall emerged in SA in summer and NSW in autumn, while significant decreases occurred in southwest Western Australia (SWWA) in winter. Important non-significant increases of 10-45 percent were also found in some States. There has been a significant 10 per cent rise in the annual Australian-average number of rain days. Significant increases of almost 20 per cent were found in the NT and NSW despite a significant 10 per cent decline in SWWA. Regionally, significant increases of 20-50 per cent have occurred in some States, with large changes in the frequency of light rainfall. Strong correlations exist between interannual variations in temperature, total rainfall, heavy rainfall and the number of rain days. Increases in Australian rainfall since 1910 are generally linked to an increase in heavy rainfall and the number of rain days. ENSO variability is partly responsible, as is enhanced monsoon activity in the 1970s and changes in other large-scale circulation features. Decreased rainfall in southwest WA is also linked to circulation changes.