Feature article

The Australian drought

Lake Okareka. [NIWA]

Total Inflows to the River Murray. (Graph courtesy of Murray-Darling Basin Commission)

Murray-Darling Basin Commission (MDBC) warns of deepening drought

The Murray-Darling Basin, stretching across South Australia, Victoria, New South Wales, and Queensland, is in area about four times the size of New Zealand. The Basin comprises the catchments of the River Murray, the Darling River, and their tributaries.

With over 40% of all crops grown commercially in Australia, the Basin is considered Australia’s most important agricultural region, and has a population of about two million people.

The MDBC, in its October Drought Update, warns that recent low rainfall has lead to some of the lowest water inflows on record into the Murray-Darling system.

According to Australia’s Bureau of Meteorology, large parts of southern and eastern Australia have seen persistent dry conditions since October 1996, a total of eleven years. The Bureau stated that 2007 was the first year in the meteorological record dating from 1900 that an El Niño drought in the Murray-Darling Basin has not been followed by at least one three-month period with above normal rainfall by the end of the following winter.

The Drought Update continues, ‘As a result of the below average rainfall in the main catchment area during August, Murray System inflows for August were only 360 gigalitres (GL), which is well below the long term August average of 1570 GL. The dry weather persisted throughout September, with inflows of about 210 GL, compared to the long term September average of 1610 GL (see figure right). Monthly inflows have now been below average for the last 24 months.’ 

A more recent report by MDBC states that during the month of October, rainfall was below average throughout the southern half of the Basin and close to average in the north. The October inflow for the River Murray System was 187 GL, The October inflow for the Murray Basin of 187 GL equals a flow rate of 70 cubic metres per second (m3/s). This ranks between the mean flow for New Zealand’s Mataura River (66 m3/s) and Mohaka River (75 m3/s). The inflow was also slightly lower than September (210 GL) and well below the long term average for October of 1420 GL.

For further reading on the River Murray System see the full Drought Update at:
http://www.mdbc.gov.au/_data/page/1366/RMSystem_Drought_Update10_October07.pdf

For more information on New Zealand climate, see: http://www.niwascience.co.nz/ncc/