Issued on 7 January 2010

Driest year on record for southwest WA

2010 with a national average of 690 mm was Australia's third wettest year on record. This was achieved despite the southwest corner of the country experiencing its driest year on record. After record spring totals, northern and eastern parts of the country continued to receive above to very much above average rainfall, with Queensland recording its wettest December on record. This is in contrast to the extremely dry conditions in the southwest of the country during 2010.

12-month rainfall deficiencies

For the 12-month period from January 2010 to December 2010, average to above average falls over the southwestern corner of WA during December 2010 were not enough to clear areas of rainfall deficiency as described in the previous drought statement. Much of the area remains in severe deficiency. Heavy rainfall over inland areas of the Gascoyne and Pilbara districts in December have largely cleared these areas of serious to severe rainfall deficiencies. With the southwest now in the climatological dry period, 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.

Recent heavy rainfall across eastern Australia has caused a dramatic reversal of dry conditions across Queensland, New South Wales and parts of Victoria and South Australia. Significantly, the Murray Darling Basin has recorded its wettest year on record, ending a sequence of below average rainfall years extending back to 2001. Spring rainfall during 2010 across much of the east was also the highest on record and December was also very wet.

Consistent rainfall in 2010 combined with high rainfall events of tropical origin caused widespread flooding of inland river systems and has resulted in a significant recovery in water storages. Across eastern Australia, storages have largely recovered to pre-drought 'levels'. In addition, both near surface (down to 20cm) and deep (20cm to 150cm) soil moistures are average or above average across most of eastern Australia. From the point of view of surface water, soil moisture and annual rainfall totals; the widespread 'long dry' which commenced in late 1996 in the far southeast of mainland Australia and late 2001 across much of the Murray-Darling Basin, has effectively ended.

While most of the country has received heavy rainfall over the past 12 months (see the Australian Annual Statement), some notable exceptions exist. In particular, south-west Western Australia has continued its long run of below average rainfall. Rainfall south and east of the Great Dividing Range has been close to average in NSW and Victoria, with Gippsland recording below average rainfall. This has resulted in a more modest recovery in Victorian water storages in contrast to NSW, Queensland and South Australia. The issue of recent rainfall and long term trends in the south-east of the continent is discussed in Special Climate Statement 22).

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