The Bureau of Meteorology (BoM) has officially announced that two major climate drivers are underway in Australia: an El Niño and a Positive Indian Ocean Dipole (IOD). These weather patterns are active over the Pacific and the Indian Ocean, potentially bringing warmer and drier-than-average conditions over summer and spring.
According to the BoM, this El Niño event is likely to persist until the end of February.
But what does an El Niño mean for Australia’s weather conditions and what do experts predict?
What is an El Niño?
The El Niño is the warm phase of the El Niño Southern Oscillation (ENSO) and it’s when waters in the central and east Pacific are warmer than normal. This is a coupled phenomenon that affects the atmosphere as clouds are pushed away from northern Australia.
The cooling phase is called the La Niña. For the past three years, Australia has been inundated with three La Niñas. As a result, Australia has experienced higher rainfall and flooding because the east Pacific waters were cooler than normal.
Now the opposite is happening.
In a normal situation, winds in the equatorial Pacific blow from east to west. However, during an El Niño event, trade winds weaken or may even reverse. This allows the warmer-than-average water to move into the central and eastern tropical Pacific Ocean. The convection migrates away from eastern Australia to the central tropical Pacific Ocean.
For Australia, this means that the clouds and rainfall that normally occur over the western Pacific and the Indonesian region move away from Australia. The El Niño’s dry conditions are felt most in eastern Australia.
What is a positive Indian Ocean Dipole?
The Indian Ocean Dipole (IOD) is the difference in sea surface temperatures between the western Indian Ocean and the eastern Indian Ocean south of Indonesia. The IOD is a significant contributor to rainfall variability in Australia as changes in temperatures can impact the rising and descending moisture and air. In a positive IOD event there are warmer sea surface temperatures in the western Indian Ocean relative to the east. As a consequence, there are easterly wind anomalies across the Indian Ocean and less cloudiness to Australia’s northwest. Hence, less rainfall over southern Australia and the Northern Territory.
What happens when both of these weather events work together?
The El Niño leads to reduced spring and early summer rainfall for eastern Australia and warmer days for southern Australia. The positive IOD further reduces spring rainfall for central and south-east Australia.
With both coupled together, their drying effect is much stronger and more widespread across Australia during spring.
Does climate change play a part in the El Niño weather pattern?
Global warming plays a significant factor on Australia’s and the global climate. From April to August 2023, sea surface temperatures reached record-breaking highs, marking an unprecedented warming trend. With global warming there is an increased chance for more extreme events to happen, according to the BoM, Australia’s climate has warmed by an average of 1.47 degrees since 1901.
The El Niño is a natural phenomenon that is not produced by climate change, however, Dr Milton Speer, a meteorologist from the University of Technology Sydney, says because of a warming planet its effects are amplified.
“What it does is it amplifies one of the effects of global warming which is to dry and warm the planet in certain areas,” he said.
Global warming is a significant factor in the warm weather Australia is experiencing this Spring, influencing record-breaking temperatures and less rainfall that has occurred in the winter months.
Dr Andréa Taschetto, a climate scientist from the University of New South Wales, says that because of climate change, there may be an increase in the frequency of the extremes of ENSO in the future.
“Extreme El Niño events and La Niña events are projected to become more frequent under global warming. If this happens in the future, then we might see more swings from droughts to floods in Australia,” she said.
Will El Niño make bushfires and droughts worse?
The last three years have seen Australia record back-to-back La Niñas. The increased rainfall has produced more bushland and more vegetation.
Dr Andrew King, a senior lecturer in climate science at the University of Melbourne, says that these warm and dry seasons can boost the likelihood of bushfire conditions.
“Especially relative to the last few years, there's a lot of vegetation that could dry out and burn,” he said.
Dr Speer expects that maximum temperatures and lack of rain will mean increased fire risk for most of southeast Australia.
“All the ground fuel and the moisture that normally in the forests and grasslands where fire occurs, that adds to the flammable nature of the landscape in El Niños,” he said.
El Niño’s impact can vary:
Dr Taschetto says that the impacts of El Niño vary and that the strength of an El Niño is not indicative of how dry and warm Australia can get.
“Moderate El Niño events that peak in the central Pacific seem to have a stronger influence on weather patterns for Australia compared to strong El Niño events that peak in the east Pacific.”
“So far we don’t know what type of El Niño event this one will be, but it suggests to be an eastern Pacific El Niño,” she says.