TEMPERATURE VARIABILITY AND EXTREMES OVER AUSTRALIA .1. RECENT OBSERVED CHANGES

Most climate change studies to date have generally focussed on changes in climatic means rather than changes in climatic extremes and variab ility and yet, from an impacts perspective, changes in the latter are likely to be at least as important. Changes in the extremes and variab ility of high-quality surface air temperature data have been analysed over Australia for the period 1961 to 1993. The mean, maximum, and min imum temperatures and the diurnal temperature range were examined. Reg ional trends in intraseasonal and interannual temperature variability were mixed and generally not statistically significant, although some seasonal changes (e.g. interannual decreases in spring) were. While in traseasonal trends were generally small overall there was a tendency f or winter increases and autumn decreases, and a weaker spring-increase , summer-decrease pattern of change. There has been a bias towards inc reases in temperature variability for the daytime and a tendency towar ds decreases in variability of overnight temperatures. Further, there was an association between warmer days (nights) and increased (decreas ed) temperature variability, particularly in the south. Through analys is of changes in the 95th and 5th daily percentile temperatures, the c ooler 'relative extremes' were found to increase at a similar rate to the median, but a little larger than rises in the warmer 'relative ext remes'. However, changes in the differences between these extremes (an alogous to low frequency intraseasonal variability) were not significa nt. Perhaps surprisingly, the most significant seasonal increase in in traseasonal temperature variability has occurred in the temperate west region in winter during a period of decreased baroclinic activity and declining rainfall totals. This study indicates that the direction of change in regional temperature variability, unlike those for actual t emperature itself, may be difficult to predict even if changes in broa dscale atmospheric circulation are evident.