A dense network of stations in Australia and New Zealand, including urbanised sites, was analysed to assess urbanisation effects on indices of extreme temperature, type of distribution change observed, and relationships with key climate drivers (El Niño – Southern Oscillation (ENSO), sea-surface temperature (SST) and mean sea-level pressure (MSLP) patterns). A strong spatial and temporal coherence of trends in extreme temperature indices was notable across both rural and urban stations, except for diurnal temperature range which was strongly influenced by urbanisation and biased by data limitations. Increased mean maximum and mean minimum temperature, general increases in hot days and warm nights, and decreases in cool days and cold nights, persisted over three analysis periods (1931-2005, 1946-2005 and 1961- 2005), with the proportion of significant trends increasing as analysis period lengthened for all indices except hot days. Rural stations had fewer significant increasing trends in warm extremes, while urbanised sites showed a greater number of significant hot day increases. Strong correlations were found between measures of mean temperature and temperature extremes, consistent across all three analysis periods and largely independent of urban status. The most common form of distributional change, for both maximum and minimum temperature, involved a significant shift in the mean and one or both extremes. However, the proportion of stations with this type of distribution shift reduced in the later period, with relatively more stations having no distribution change, or shifts in the mean (but not extremes) over 1961-2005, possibly due to a change in the relationship between ENSO and temperature and/or the effects of rapid population growth since the 1950s. This study indicates that measures of ENSO, such as NINO3.4 or our second MSLP pattern, have the potential to better predict temperature extremes over large areas of Australasia, especially eastern Australia, comp
Chambers et al. (Sat,) studied this question.