Confidence in specific areas of rainfall change derived from climate models is not as great as the confidence in temperature change. Although all the main models see large changes—positive and negative—particularly in the tropical regions, they do not always agree exactly where those changes will be. In very general terms, equatorial regions will experience relatively severe changes with either more or less rain depending on the region; temperate regions will experience a decrease to mild increase; and polar regions are modelled to receive a moderate to pronounced increase in precipitation. Most models find that global average precipitation increases with time, as the hydrological cycle is enhanced by global warming. It changes most in high latitudes and in the Indian monsoon, and changes least in the subtropics.
Multi-model mean changes in precipitation (millimetres per day) 2080–2099 relative to 1980–1999 (SRES A1B scenario). Stippling shows at least 80 per cent of models agree on the sign of the mean change.
Source: Intergovernmental Panel on Climate Change, Fourth Assessment Report, Working Group I Report—The physical science basis, Chapter 10, p. 769.
A warmer atmosphere can hold more water vapour, which means that evaporation will increase and rainfall may become heavier. Changes in wind patterns and sea surface temperatures will also influence the amount and location of rainfall. Australia's rainfall is highly variable and linked to phenomena such as the South Asian monsoon, tropical cyclones, the strength and latitude of the mid-latitude westerly winds, and the El Niño-Southern Oscillation (ENSO). Changes in rainfall due to ANTHROPOGENIC climate change will therefore depend on the response of these phenomena.
Australia stretches from the tropics to well into the temperate regions. Monsoonal areas are predicted to experience increased rainfall, which may extend into parts of the arid interior, over much of the Great Artesian Basin and northern savannahs. However, the rest of Australia, including most of Western Australia, South Australia, Victoria and New South Wales, is predicted to receive less precipitation. Whilst this decrease is modelled to be slight, the already highly variable climate in Australia, coupled with the nature of our farming systems and the fragility of natural ecosystems, suggests that even a slight change could have a significant impact.
Intergovernmental Panel on Climate Change, Contribution of Working Group I to the Fourth Assessment Report, Climate Change 2007: The Physical Science Basis, Chapter 10, Global Climate Projections.