Inter-annual rainfall variability in arid Australia: greater than elsewhere?
Faculty of Computing, Health and Science
School of Natural Sciences / Centre for Ecosystem Management
The often espoused view that Australia's arid zone experiences more variable rainfall over time than areas of similar climates elsewhere was tested using annual rainfall data from 407 localities spread throughout 14 arid areas, including 68 Australian sites. This represents an updated and more comprehensive analysis than previously completed. Four measures of inter-annual rainfall variability were calculated. Two of these are commonly used in the literature: the variability index (spread of the 90th and 10th percentiles divided by the median rainfall) and the coefficient of variability (standard deviation as a percentage of the mean). In addition, two simpler measures not divided by the average annual rainfall were used: the difference between the 90th and 10th percentiles, and the standard deviation of the mean. Linear relationships between rainfall variability and average annual rainfall enabled analysis of covariance (ANCOVA) to be employed, with appropriate post hoc testing of adjusted means, to determine differences between regions in terms of the various measures of rainfall variability. ANCOVA consistently revealed that four regions (Thar, Namib-Kalahari, Somali and northern Australian deserts) were significantly more variable than all others. Southern Australia (defined as south of 27°S latitude) was grouped with these other desert regions, which include the North American deserts, Sahel, northern Sahara and Karoo. Generally the two groups were divided into low latitude, summer rainfall regions and higher latitude, winter rainfall ones, although there were some clear anomalies. The findings suggest that comparative studies of biotic responses to rainfall variability between arid Australia (particular southern regions) and other deserts are warranted before paradigms and models based on the uniqueness of Australia's arid environment are accepted.