AUSTRALIAN RAINFALL TRENDS DURING THE 20TH-CENTURY

A set of high-quality rainfall records is used to examine rainfall trends over Australia during the twentieth century. The 191 stations used have been selected by an exhaustive search of documentation regarding instrumentation, observational practices, site relocations, and exposure. Statistical tests of the reliability of observing practices also have been applied in the selection process, as well as tests to detect inhomogeneities. The data set used is the most reliable available for monitoring rainfall trends during the twentieth century. The data have been clustered objectively into groups exhibiting similar variations in annual rainfall. A subset of 10 stations (one for each cluster) suitable for long-term monitoring of rainfall trends is selected. The trends in annual, winter, and summer rainfall are exhibited. The study confirms trends noted in earlier studies. Summer rainfall over much of eastern Australia increased abruptly around 1950. In the south-west of the continent most stations recorded a smoother trend to lower winter rainfall, although there is a small area with increased rainfall. The identification of these trends in this study indicates that they are not the result of unreliable observations or to doubtful compositing of stations into groups. These trends have now continued for some decades after their initial observation. It is possible, however, that the twentieth century trends simply reflect a return to conditions of the late nineteenth century, rather than a trend that could be unambiguously attributed to an enhanced 'greenhouse effect'.