Issued 5 June 2009
A very dry start to the year for much of southeast and southwestern Australia
Rainfall was below to very much below average across most of the continent during May 2009. Another month of low rainfall for southern Australia exacerbated already dry conditions. Victoria has now experienced its third driest start to the year on record and southwestern WA its fifth driest since reliable records commenced in 1900. Short-term rainfall deficits are now evident over most of southeast and southwestern Australia.
Across northern Australia, an early end to the wet season has seen short-term rainfall deficits develop on a 3-month scale over the Queensland Gulf Country, the north of the NT and the north Kimberley. This is a contrast to the very wet January and February that was observed across northern Australia earlier this year.
Rainfall deficiency maps for standard periods out to three years are available.
5-month rainfall deficiencies
For the 5-month period from January to May 2009, serious to severe rainfall deficiencies are evident over much of southwest WA, especially near the west coast, and across Victoria. A few areas of serious to severe deficiencies are also evident over southeast SA, northeast Tasmania and far southern border areas of NSW. Several sites in the Lower West and Southwest districts of WA recorded lowest rainfall on record, as did a few sites in central Victoria. Perth and Melbourne both fell just short of their all time lowest on record rainfall for the 5-month period by only a few millimeters. Rainfall was close to average in southwest WA in March and over southeast Victoria in March and April. In all other months of the 5-month period, rainfall over southeast and southwestern Australia was below to very much below average.
24-month rainfall deficiencies
For the 24-month period from June 2007 to May 2009, serious to severe rainfall deficiencies are evident across much of southeast Australia and parts of central Australia. These deficiencies cover most of the agricultural areas of SA, central and western Victoria, eastern and northern Tasmania and some southern border areas of NSW. Although deficits for periods of three or more years linger in parts of southeast Queensland and northeast NSW, for the 24-month period to May 2009 these areas benefited from above average rainfall associated with the 2007/08 La Niña and from recent above average rainfall in April and May 2009. However, in southeastern and central Australia, apart from wet November and December periods in both 2007 and 2008, rainfall was generally below to very much below average through the period.
During the 24-month period two sustained periods of positive Indian Ocean Dipole (IOD) mode were observed. The two periods extended over the winter and spring months of both 2007 and 2008. Positive IOD events are historically associated with lower than normal winter and spring rainfall over central and southern Australia. Therefore, the consecutive positive IOD events of 2007 and 2008 partly explain winter and spring rainfall deficits through the 24-month period. About IOD.
Very long-term rainfall deficiencies outside of the usual drought periods persist across parts of southern and eastern Australia. Most notably, rainfall has been below average across much of southwest and southeast Australia since 1997, while the Murray Darling Basin has experienced below average rainfall since 2002.