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Associations between rainfall variability in the southwest and southeast of Australia and their evolution through time

Significant rainfall declines have been observed across much of southern Australia over the last 50 years. In particular, strong declines occurred in the southwest of Western Australia (SWWA) from the late 1960s with further declines in the late 1990s, and in the southwest of eastern Australia (SWEA) from the mid‐1990s. As a result, most communities in these regions are facing water shortages. Meteorologically, the regions share a common winter‐maximum rainfall regime, with peak rainfall occurring from May to October. In both regions, the declines have mainly occurred in the early part of the winter half‐year (May–June–July, MJJ). This study aims to assess if there is an association between rainfall variability in these two regions on a range of time‐scales and whether that association has altered with the recent rainfall declines. Rainfall variability in the two regions is significantly related. On synoptic time‐scales, a weak but significant relationship was found in each month of the winter half‐year due to rain‐bearing disturbances travelling along the storm track affecting the two regions with a lag of approximately 3 days. On interannual time‐scales, the relationship is stronger because of the high correlation between mean sea‐level pressures (MSLP) over both regions. MJJ MSLP has seen significant increases over the last 50 years in both regions, reaching record values in 2006. In recent decades the interannual association between early winter rainfall totals has strengthened, however this is due in part to the decreasing variance at each location. The variability of the associations between these two regions provides a background on which to explore the strength and variability of the drivers that influence rainfall variability across southern Australia. Copyright © 2009 Royal Meteorological Society