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Sunday, July 6, 2008

CSIRO and BOM Drought Review

The Australian Government has released the first phase of a three part review of the conditions under which drought assistance is provided accounting for both recent observed changes in climate as well as projected changes in the decades ahead. The research conducted by the CSIRO and the Australian Bureau of Meteorology drew several conclusions about recent and future trends:

The analysis shows that the areal extent and frequency of exceptionally hot
years have been increasing rapidly over recent decades and this trend is
expected to continue. Further, over the past 40 years (1968-2007), exceptionally
hot years are typically occurring over 10-12% of the area in each region,
i.e. about twice the expected long term average of 5%. By 2010-2040, the mean area is likely to increase to 60-80%, with a low scenario of 40-60%, and a high scenario of 80-95%.


On average, exceptionally high temperatures are likely to occur every 1-2 years.
Observed trends in exceptionally low rainfall years are highly dependent on the period of analysis due to large variability between decades. If rainfall were the sole trigger for EC declarations, then the mean projections for 2010-2040 indicate that more declarations would be likely, and over larger areas, in the SW, SWWA and Vic&Tas regions, with little detectable change in the other regions. Under the high scenario, EC declarations would likely be triggered about twice as often and over twice the area in all regions. In SWWA the frequency and areas covered would likely be even greater.

Projected increases in the areal extent and frequency of exceptionally low soil moisture years are slightly clearer than those for rainfall. If soil moisture were the sole criterion for EC declarations, then the mean projections indicate that more
declarations would be likely by 2030, particularly in the SW, SW WA and Vic&Tas regions. Under the high scenario, EC declarations would be triggered almost twice as often in most regions and almost four times as often in SWWA.


Most importantly, the report concludes that the current standard by which 'exceptional circumstances' are declared (a 1 in 20-25 year drought event) "is not appropriate under a changing climate."

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