The Bureau of Meteorology last week declared El Niño and a positive Indian Ocean Dipole (IOD) are underway.
Under the influence of these two climate drivers, warmer and drier conditions are more likely over spring and summer for parts of Australia.
Bureau of Meteorology climate manager Dr Karl Braganza said both El Niño and a positive Indian Ocean Dipole (IOD) may 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 have 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.”
El Niño events increase the risk of extreme temperature shifts, such as heatwaves and hotter days.
A positive IOD will heighten fire risks over southeast Australia in spring, while El Niño will heighten fire risk there over both spring and summer.
The Bureau made the El Niño declaration 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 could 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 about 16 positive IOD and 15 El Niño years.
Seven years have seen positive IOD and El Niño events happen at the same time.
The outlook has shifted to El Niño, having met criteria 1, 3 and 4 – see below.
* Climate models suggest this El Niño is likely to continue until at least the end of the southern hemisphere summer 2023–24.
* The outlook will remain at El Niño until this event decays or signs of a possible La Niña appear.
An El Niño has been declared, with three of the following criteria satisfied:
1. Sea surface temperature: Temperatures in the NINO3 or NINO3.4 regions of the Pacific Ocean are 0.8 °C warmer than average.
3. SOI: The three-month average Southern Oscillation Index is –7 or lower.
4. Models: A majority of surveyed climate models show sustained warming to at least 0.8 °C above average in the NINO3 or NINO3.4 regions of the Pacific until the end of the year.
