Issued on 3 November 2010
Rainfall deficiencies persist in western WA
Following Australia's wettest September on record, Australia recorded its third wettest October on record in 2010. However, widespread above-average rainfall again missed western parts of WA, and particularly the southwest corner, which is experiencing its driest year-to-date on record (34 mm below the previous record of 390 mm) and its driest November to October on record (see Special Climate Statement 21). Northern and eastern parts of the country have continued to receive above to very much above average rainfall, with the Northern Territory recording its wettest October on record. The Northern Territory has also recorded its second wettest January to October period on record whilst Queensland and the MDB have recorded their fourth wettest, the wettest since 1974 for both areas. Furthermore, the May-October period (normally the dry season) has been the wettest on record for the northern half of Australia. Rainfall in recent months has cleared a number of short-term rainfall deficiencies across eastern Australia. However, the rains in 2010 have only made limited inroads into the serious deficiencies which remain on multi-year time-scales, especially in southeastern and southwestern Australia and southeast Queensland, and continue to affect water supplies; to alleviate these would require above average rainfall for a sustained period (Special Climate Statement 22).
10-month rainfall deficiencies
For the 10-month period from January 2010 to October 2010, below average falls over the southwestern half of WA during October 2010 has maintained areas of rainfall deficiency as described in the previous drought statement and slightly increased areas of lowest on record. Some average to above average falls over inland areas of the Gascoyne and Pilbara districts have not been enough to clear the region of serious to severe rainfall deficiencies, with large areas still remaining. To relieve these areas of rainfall deficiency in WA, i.e. to just get above the tenth percentile, rainfall for the remaining two months of the year will have to be very much above average, i.e. in the highest 10% of such periods on record, over large areas. In a coastal strip in the southwest corner between Lancelin and Walpole, rainfall for 2010 will be in the 10th percentile even if rainfall for the last two months of the year matches the highest on record.
Whilst recent rains in eastern Australia have provided, in many cases, short-term relief, sustained periods of above-average rainfall are needed to remove very long-term deficiencies. This is especially true for the very long-term deficiency periods of 9 and 14 years (see the Special Climate Statement 22). Rainfall has been below average across much of southwest and southeast Australia since 1997, whilst central and southern parts of the Murray-Darling Basin have experienced below average rainfall since 2002. These long-term deficiencies have taken place against a background of well above average temperatures, including Australia's warmest decade on record. Further information on exceptional rainfall and temperature events across Australia can be found in the Special Climate Statements.
Lowest on record - lowest in the historical analysis, which runs from 1900.
Severe deficiency - rainfalls in the lowest 5% of historical totals.
Serious deficiency - rainfalls in the lowest 10% of historical totals, but not in the lowest 5%.
Very much below average - rainfalls in the lowest 10% of historical totals.
Below average - rainfalls in the lowest 30% of historical totals, but not in the lowest 10%.
Average - rainfalls in the middle 40% of historical totals.
Above average - rainfalls in the highest 30% of historical totals, but not in the highest 10%.
Very much above average - rainfalls in the highest 10% of historical totals.
Product Code IDCKGD0AR0