Issued 6 April 2009
Long-term rainfall deficiencies persist over southeastern Australia
A dry start to the year across southeastern and central Australia has been followed by generally average to above average rainfall in March. In contrast, a wet start to the year across northern Australia has been followed by generally below to very much below average March rainfall.
Drought periods greater than 3 months and less than 12 months generally show only small and isolated areas of rainfall totals in the lowest 10% of historical records. For drought periods of 3 months or less short-term deficiencies are evident over southeastern Australia, due to the dry start to 2009 mentioned above. Victoria had its third-driest January-March on record. For drought periods greater than 12 months, significant areas of rainfall deficiencies are evident, but vary in location and intensity depending on the period selected. The 15 and 22-month periods have been chosen for this statement as they show some of the largest areal extent of deficits across the country. Rainfall deficiency maps for standard periods out to three years are available.
15-month rainfall deficiencies
For the 15-month period from January 2008 to March 2009, rainfall was generally above to very much above average across the far north and far west of the country, but below to very much below average across central and southeastern Australia. Areas of serious to severe rainfall deficiencies for the period are evident across most of southern and western Victoria and most of the agricultural areas of SA, parts of central Australia, eastern Tasmania and the far south-east of NSW extending into the far east of Victoria.
22-month rainfall deficiencies
For the 22-month period from June 2007 to March 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 parts of the far southern inland of NSW. A small area of lowest of record is evident in the Wimmera district of Victoria. Although deficits for periods of three or more years linger in parts of southeast Queensland and northeast NSW, for the 22-month period to March 2009 these areas benefited from above average rainfall associated with the 2007/08 La Niña. However, in southeastern and central Australia, apart from wet November-December periods in both 2007 and 2008, rainfall was generally below to very much below average.
The Indian Ocean Dipole (IOD) is a pattern of sea surface variability across the Indian Ocean that is associated with lower than normal rainfall over central and southern Australia when it is in a positive phase (see IOD). Both 2007 and 2008 were consecutive years of sustained positive IOD, which partly explains rainfall deficits through the 22-month period in these areas. The IOD usually has its greatest impacts between June and November.
The deficiencies discussed above have occurred against a backdrop of decade-long rainfall deficits and record high temperatures that have severely stressed water supplies in the east and southwest of the country. The combination of record heat and widespread drought during the past five to twelve years over large parts of southern and eastern Australia is without historical precedent and is, at least partly, a result of climate change.