The Bureau of Meteorology (BoM) has officially declared that both an El Niño and a positive Indian Ocean Dipole (IOD) are underway. These two climate drivers are likely to lead to warmer and drier conditions for parts of Australia. El Niño events increase the risk of extreme temperature shifts, like heatwaves and hotter days, as well as increased fire danger across the south-east of Australia in spring and summer. Meanwhile, a positive IOD also contributes to greater fire risk across southeast Australia during springtime. When these two climate events occur together, their drying effect is typically stronger, and more widespread across the country.
The news comes after Australia experienced its warmest winter on record, when the national mean temperature was 1.53 °C above the 1961–1990 average for winter, making it the warmest on record since national observations began in 1910.
El Niño and positive Indian Ocean Dipole
According to the BoM Climate Manager, Dr Karl Braganza, the two climate events will 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,” said Dr Braganza. “The Bureau’s three-month forecast for Australian rainfall and temperature have been indicated 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.”
While the World Meteorological Organization declared the onset of El Niño in July, BoM waited until three of the four El Niño criteria were met.
This criteria include:
- Sea surface temperature – temperatures in regions of the Pacific Ocean are 0.8 °C warmer than average
- Southern Oscillation Index (SOI) – this index measures the difference in surface air pressure between Tahiti and Darwin. Sustained positive values about +8 indicate a La Niña event while sustained negative values below about –8 indicate an El Niño. In this case, the 90-day average has been about -7.7.
- Models – a majority of surveyed climate models show sustained warming in regions of the Pacific until the end of the year. Models for this El Niño event indicate that it is likely to persist until the end of February.
Meanwhile, a positive IOD is underway, and will likely persist until the end of spring. This will lead to reduced spring rainfall in central and south-east Australia. This natural climate cycle comes from sustained changes in the difference between sea surface temperatures in the tropical western and eastern Indian Ocean.
The last time an El Niño and positive IOD occurred together was in 2015. Stay up-to-date with climate information here.