An Assessment of the Impact of Climate Change on the Nature and Frequency of Exceptional Climatic Events: Drought - Exceptional Circumstances

The Australian Government commissioned the Bureau of Meteorology and the Commonwealth Scientific and Industrial Research Organisation (CSIRO) to undertake a climatic assessment of the likely future climate patterns and the current Exceptional Circumstances standard of a one-in-20-to-25-year-event.

The Australian Government is conducting a comprehensive national review of drought policy. The review includes three separate assessments.The first examines the implications of future climate change for the current exceptional circumstances (EC) standard of a one in 20-25 year event and is provided in this report. The others cover economic and social aspects.

This study analyses changes in the areal extent and frequency of exceptionally high temperatures, low rainfall and low soil moisture for seven Australian regions (see Figure 1): Queensland (Qld); New South Wales (NSW); Victoria and Tasmania (Vic&Tas); the northwest (NW); the southwest (SW); the southwest of WA (SW WA); and the Murray-Darling Basin (MDB). The analysis uses observed and simulated data covering varying periods from 1900 to 2040. Low, mean and high projections are given for future years.

The uncertainties associated with the historical data and the climate projections are noted, including the qualitative assessment that the temperature data have the lowest uncertainty, that there is higher uncertainty with the rainfall data, and that the soil moisture data – being derived from a combination of rainfall data, low resolution observations of evaporation, and modelling – are the least reliable.