An assessment of recent trends in Australian rainfall

Studies over the last decade into Australian rainfall have often noted the presence of long-term and shortterm trends but have rarely identified any statistically significant trends, mainly because the data are characterised by high interannual variability. The only exception is the southwest region of Western Australia (SWWA) where a relatively sudden decrease in winter season (and annual) rainfall of about 20 per cent occurred around the 1970s. Reliable long-term trend analyses have been made possible because of the application of extensive quality-control procedures and the identification of highquality station records (Lavery et al. 1992) and composite records (Lavery et al.1997) that go back as far as the beginning of the twentieth century. Many individual records extend further back in time. Nicholls and Lavery (1992) analysed 191 high-quality station records and confirmed the results of earlier studies that identified long-term decreases in winter rainfall over southwest Western Australia and increases in summer rainfall over parts of eastern Australia. They noted the relatively poor geographical coverage of Western Australia and also noted that trends since 1900 needed to be assessed against evidence that conditions during the late twentieth century may have been similar to those of the late nineteenth century. Suppiah and Hennessy (1996) looked at trends in a number of rainfall statistics over the period 1910 to 1989 using daily data from 53 stations. Following the study by Nicholls and Lavery (1992), Suppiah and Aust. Met. Mag. 53 (2004) 163-173