RAINFALL

Rainfall is highly variable between regions, seasons and years. Fluctuations from drought to floods are associated with the Southern Oscillation phenomenon (notably the El Nino events). A dramatic illustration of this variability is the major flooding following an estimated 403 cubic kilometres (403,000 GL) of rainfall which fell across the Northern Territory and Queensland over a 10 day period ending 3 March 2010 (BOM 2010c).

Australia's rainfall in 2009 was 453mm, which was slightly below the long-term average (1961-1990) of 464mm (BOM 2010b).

The impact of varied and unreliable rainfall is felt mainly by the agricultural sector where prolonged droughts in many areas have severely limited water availability to non-irrigated holdings and, in more recent years, irrigated holdings as well. The area of irrigated agricultural land in Australia decreased by 31% between 2005-06 and 2008-09, and the volume of water applied over the same period decreased by 39% (ABS 2009).

Urban settlements have also been affected by low rainfall over catchment areas. Many major cities and towns have had mandatory water restrictions in place for several years and government funded programs have also been employed to facilitate the installation of low-flow shower heads, dual flush toilets and water tanks. In order to augment water supplies, several states have already commissioned large desalination plants. The total capacity of plants servicing major cities is expected to rise to over 450 GL/year by 2013, a ten-fold increase from 2006 (CSIRO 2009a).

Because of the highly varied nature of Australia's rainfall, measures of total rainfall and rainfall anomalies in key regions are considered more useful indicators of the impacts of dry conditions than Australia-wide data. The Murray Darling Basin contains Australia's major agricultural areas, and for this reason, data for this region is shown. Even over the Murray-Darling Basin, the annual rainfall has been quite variable over time. The annual rainfall anomaly shows nine consecutive years (from 2001 to 2009) of below the long-term average rainfall, which is the longest length of time of below average rainfall since records began in 1900.