Temperature variability and extremes over Australia: part 1 - recent observed changes

Most climate change studies to date have generally focussed on changes in climatic means rather than change. in climatic extremes and satiability and yet, from an impact. permathe. change, in the latter are likely to be at least as important. Change, in the extremes and variability of high-quality surface air temperature data base been analysed over Australia for the period 1961 to 1993. The mean, maximum. and minimum temperatures and the diurnal temperature range were examined. Regional 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 intrmeasortal trends wen-generally small overall there Ins* tendency for winter increas-es and autumn decreases. and a weaker apring.Incrta.e. sum-mer-decrease pattern of change. There has been a bias towards Increases in temperature variability for the daytime and a tendency towards decrease, in satiability of overnight tempera-tures. Further, there was an association between wanner days (nights) and increased (decreased) temperature satiability. particularly in the south. Through analysis of changes in the 95th and 5th daily percentile temperatures, the cooler 'relative extremes' were found to increase at a similar rate to the medi-an, but a little larger than rises in the wanner 'relative extremes', However. changes in the differences between these extremes (analogous to low frequency intraseasonal variabili. ty) were not significant. Perhaps surprisingly. the most significant seasonal increase in intraseasonal temperature variability has occurred in the temperate west region in winter during a period of decreased baruclinic activity and declining rainfall totals. This study indicates that the direction of change In regional temper-ature variability. unlike Muse for actual temperature itself. may be difficult to predict even if changes in broadscale atmospheric circulation are evident.