Drought and its Causes
What is drought?
The Bureau of Meteorology describes drought as a prolonged, abnormally dry period when there is not enough water to meet normal or expected needs.
We regard drought as a normal part of climate variability that must be managed.
During drought, less rain (and snow) falls in the mountains, so less runoff comes down into our rivers, creeks and water supply reservoirs.
To make matters worse, the soil in the catchments rarely gets wet enough to generate decent runoff into the reservoirs. Over long periods of time this can contribute to extended reductions in streamflow.
Climate change can also magnify the impacts of drought.
Drought may last a few months or many years. The current drought that is devastating Victoria and other parts of southern Australia has lasted for 13 years. Other examples of severe droughts in Melbourne were the 1939 to 1945 drought and the Federation drought which ran from 1895 to 1903. We support ongoing research into the causes and extent of drought across South East Australia, including research through the South Eastern Australia Climate Initiative.
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What causes drought?
The main cause of drought in eastern Australia is El Niño - the extensive warming of the central and eastern Pacific Ocean that leads to a major shift in weather patterns across the Pacific.
El Niño affects runoff in catchments serving all major water supply systems in eastern Australia.
El Niño events have occurred in 1997/98, 2002/03 and 2006/07. The last big El Niño event was in 1998, which was also the hottest year on record.
While the science of predicting weather and drought has improved since the use of weather satellites began in the 1960s, it remains imperfect. It is important to remember that not all droughts occur in El Niño years or can be predicted this way.
La Niña, the reverse of the El Niño effect, relates to changes in atmospheric conditions and ocean circulation. In Australia, especially the eastern part of Australia, La Niña events are associated with an increased probability of wetter conditions. The most recent strong La Niña was 1988/89, with a moderate event for about three years at the turn of the century.
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