Issued on 7 February 2011

A wet January for southwest WA but deficiencies remain

All states and territories recorded above median rainfall in January 2011. Much of the southwest corner of WA recorded very much above average rainfall, resulting in its sixth wettest January on record. Rainfall in December 2010 and January 2011 ended a sequence of 8 months with below average rainfall, with 2010 being the driest year on record for the region.

13-month rainfall deficiencies

For the 13-month period from January 2010 to January 2011, average to above average falls over the southwestern corner of WA during January 2011 were not enough to clear areas of rainfall deficiency as described in the previous drought statement. Above average rainfall recorded in the southwest during January was able to reduce the extent of severe and lowest on record deficiencies. However, the size of the deficiencies and the fact that the southwest is now in the climatological dry season means it is very unlikely that deficiencies will be removed in coming months. To relieve most areas of rainfall deficiency in southwest WA, i.e. to just get above the tenth percentile, rainfall for the next three months will have to be in the top 10% wettest such periods on record. For the southwest corner adjacent to the coast, rainfall would have to exceed the highest on record.

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Definitions

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.

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