Issued on 2 July 2010

Short-term deficits worsen over southwestern WA

Below average falls over much of the country in June 2010, especially in southwest WA, has contributed to an increase in serious to severe deficiencies in this area. It has been the third driest start to the year for this region since records began in 1900. Despite the drier than average June in many parts of Australia, northern and eastern states have still recorded an above to very much above average first six months over large areas, with Queensland having its wettest start to the year since 1981, despite a dry May and June. While rainfall in recent months has cleared a number of short-term rainfall deficiencies across eastern Australia, serious deficiencies remain on multi-year time-scales, especially in southeastern Australia, and continue to affect water supplies; to alleviate these would require above average rainfall for a sustained period.

6-month rainfall deficiencies

For the 6-month period from January to June 2010 serious to severe deficiencies are evident over much of western WA. Above average rainfall during June on the North West Cape, and a small adjacent region inland has cleared rainfall deficiencies in this area. In contrast, below average rainfall in southwestern parts of the state has led to a substantial expansion of deficiencies in this area. The far southwest region shows an area of lowest on record rainfall for the period. Elsewhere, there is a region of serious to severe deficiency in southeastern Tasmania, which has intensified slightly in the past month.

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15-month rainfall deficiencies

For the 15-month period from April 2009 to June 2010, below average falls over the western half of WA during June 2010 further exacerbated areas of rainfall deficiency as described in the previous drought statement, with areas of serious to severe deficiency becoming much more extensive in the southwest part of the state. Above average falls on the North West Cape and immediately adjacent inland areas during June have cleared rainfall deficiencies in this area at this timescale. However, serious to severe rainfall deficiencies remain evident over much of the Pilbara and Gascoyne districts.

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 8 and 13 years (see the drought statement archive). 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.

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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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