Trends in total rainfall, heavy rain events and number of dry days in Australia, 1910–1990

Abstract

Trends in heavy rainfall, total rainfall and number of dry days in Australia have been analysed using daily rainfall records at 125 stations. Summer and winter halves of the year were considered separately for the period 1910–1990. The summer half-year is defined as November–April, while the winter-half is May–October. Heavy rainfall is defined as the 90th and 95th percentiles of daily rainfall in each half-year. The magnitude of trends was derived from linear regression while statistical significance was determined by Kendall-Tau and field significance tests. Increasing trends in heavy rainfall and total rainfall have occurred during the summer half-year, but only 10–20% of stations have statistically significant trends. During the winter half-year, heavy rainfall and total rainfall have also increased, except in far southwest Western Australia and inland Queensland. There has been a reduction in the number of dry days in both halves of the year, except in far southwest Western Australia and at a few stations in eastern Australia where there has been an increase in the number of dry days in the winter half-year. Changes in the number of dry days were statistically significant at over 50% of stations. Hence there are regions showing coherent increases and decreases in rainfall which may be due to systematic changes in climate during the last century. Trends were averaged over three broad regions with adequate station coverage. There has been a general decrease in dry days with an increase in total and heavy rainfall intensity in the northeast and southeast, and a decrease in total and heavy rainfall in the southwest. These rainfall changes are related to changes in other climate variables such as temperature and cloud cover in Australia. © 1998 Royal Meteorological Society