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Will the drying trend in southwest Australia continue under future greenhouse scenarios?

PI: Pandora Hope
Institution: Australian Bureau of Meteorology
Additional Investigators: Steve Charles, Bertrand Timbal
The southwest of Australia generally receives consistent, reliable winter rainfall. In the mid 1970s there was a shift to consistently drier conditions. The decline has been one of the most dramatic and sustained of anywhere in the world. A research programme examining the drivers of the decline found that the change is likely attributable in large part to greenhouse warming (IOCI 2002). This highlights that the precipitation in this small region might be highly sensitive to the climate changes resulting from increasing greenhouse gases. It would be of great interest to investigate how the drying trend in the southwest of Australia develops under different scenarios for the future.

The direct precipitation totals from GCMs and reanlyses have traditionally not captured the decline in the southwest of Australia well. Two down-scaling techniques have used larger scale features to more accurately capture the trend (Charles et al. 1999a, Timbal 2004). The rainfall decline is also shown by the decrease in synoptic types associated with wet conditions (Hope 2004). The three techniques will be applied to the daily CMIP output for the 20C3M simulation to determine how well the models simulate the rainfall changes in the recent past.

Earlier studies have found that the present day analogues are adequate for representing the rainfall in a future climate (Charles et al. 1999b). Discovering the rainfall response in a range of future climates will be of advantage to the local water authorities and to the wider scientific community as an example of the local impact of global climate change on a highly sensitive region.

Charles, S.P., B.C. Bates and J.P. Hughes, 1999a: A spatiotemporal model for downscaling precipitation occurrence and amounts. Journal of Geophysical Research, 104(D24), 31657-31669
Charles S.P., B.C. Bates, P.H. Whetton and J.P. Hughes, 1999b: Validation of downscaling models for changed climate conditions: case study of southwestern Australia. Climate Research, 12, 1-14
Hope P., 2004: Shifts in synoptic types affecting rainfall in southwest Australia. in preparation
IOCI, 2002: Climate variability and change in south west Western Australia. Indian Ocean Climate Initiative Panel, 34pp
Timbal, B, 2004: Southwest Australia past and future rainfall trends. Climate Research, 26, 233-249
  • Hope, P.K., 2006: Projected future changes in synoptic systems influencing southwest Western Australia. Clim. Dyn., DOI: 10.1007/s00382-006-0116-x. Abstract. Full Article. Edit.
  • Hope, P.K., W. Drosdowsky and N. Nicholls, 2006: Shifts in the synoptic systems influencing southwest Western Australia. Clim. Dyn., DOI: 10.1007/s00382-006-0115-y. Abstract. Full Article. Edit.

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