Warmer and drier conditions will be more likely over spring and summer for parts of Australia, under the influence of these two climate drivers.
Bureau of Meteorology climate manager Karl Braganza said both El Niño and a positive Indian Ocean Dipole tend to draw rain away from Australia.
“Over spring, their combined impact can increase the chance of below average rainfall over much of the continent and higher temperatures across the southern two-thirds of the country,” Dr Braganza said.
“The bureau’s three-month forecast for Australian rainfall and temperature has been indicating warm and dry conditions for some time.
“An established El Niño and positive IOD reinforces our confidence in those predictions.
“Based on history, it is now also more likely that warm and dry conditions will persist over eastern Australia until autumn [in 2024].”
El Niño events increase the risk of extreme temperature shifts, like heatwaves and hotter days.
Increased fire danger in south-eastern Australia is associated with El Niño conditions.
A positive IOD contributes to greater fire risk over south-east Australia in spring, while El Niño contributes to elevated fire risk over both spring and summer.
The bureau made the El Niño declaration on September 19 after three of the four El Niño criteria were met, including a sustained response in the atmospheric circulation above the tropical Pacific.
The last time Australia encountered both El Niño and a positive IOD was in 2015.
“Around two-thirds of Australia’s driest years on record were during El Niño however, no two El Niño or IOD events or their impacts are the same,” Dr Braganza said.
“El Niño is part of a natural climate cycle that affects global weather and occurs on average every three to five years.”
Bureau senior climatologist Catherine Ganter said the Indian Ocean Dipole can have as large an influence on Australia’s rainfall and temperature as El Niño.
“A positive IOD often results in below average rainfall during spring for much of central and southern Australia and warmer than average maximum temperatures for the southern two-thirds of Australia,” Ms Ganter said.
“Similar to El Niño, the IOD describes a natural climate cycle brought about by sustained changes in the difference between sea surface temperatures in the tropical western and eastern Indian Ocean.”
Since 1960, when reliable records began for the IOD, there have been around 16 positive IOD and 15 El Niño years. Seven years have seen positive IOD and El Niño events happen at the same time
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