Rainfall in Australia’s eastern seaboard: a review of confidence in projections based on observations and physical processes

There is a high degree of variation in rainfall projections for later this century for Australia's eastern seaboard, partly because of how different climate models represent the relevant physical processes. These processes include local environmental conditions, synoptic phenomena and large-scale atmospheric and oceanic modes of variability. We review these processes using a wide range of analyses from observations and modelling. A synthesis of this review is used to produce likelihood and confidence measures for the rainfall projections, intended to inform planning and adaptation. The most likely projected outcome in southeast Queensland is a small decrease in rainfall for all seasons, with higher confidence in autumn than other seasons due to uncertainties associated with representing the El Niño-Southern Oscillation, thunderstorms, tropical cyclones and the monsoon. In northeast New South Wales (NSW), there is projected to be a small increase for summer, little change for autumn, a decrease for winter and a small decrease for spring, with confidence being highest in winter and lowest in summer. These projections correspond to an intensification of the annual cycle in northeast NSW. Natural variability in mean rainfall is projected to remain significant in comparison to the climate change signal throughout the eastern seaboard region. In contrast to mean rainfall, there is high confidence in a projected increase in the frequency of extreme rainfall throughout this region.