TRENDS IN TOTAL RAINFALL, HEAVY RAIN EVENTS AND NUMBER OF DRY DAYS INAUSTRALIA, 1910-1990

Trends in heavy rainfall, total rainfall and number of dry days in Aus tralia 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-Apri l, 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 statisti cal significance was determined by Kendall-Tau and field significance tests. Increasing trends in heavy rainfall and total rainfall have occ urred during the summer half-year, but only 10-20% of stations have st atistically significant trends. During the winter half-year, heavy rai nfall 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 sout hwest Western Australia and at a few stations in eastern Australia whe re 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 signif icant at over 50% of stations. Hence there are regions showing coheren t increases and decreases in rainfall which may be due to systematic c hanges in climate during the last century. Trends were averaged over t hree broad regions with adequate station coverage. There has been a ge neral decrease in dry days with an increase in total and heavy rainfal l intensity in the northeast and southeast, and a decrease in total an d heavy rainfall in the southwest. These rainfall changes are related to changes in other climate variables such as temperature and cloud co ver in Australia. (C) 1998 Royal Meteorological Society.