The Bureau of Meteorology (BOM) has reset the outlook for the El Niño Southern Oscillation to inactive, which means La Niña 2020-2021 is over.
BOM climatologist Naomi Benger, however, stressed that this does not mean it will be all blue skies for the foreseeable future.
“What this really means is that La Niña no longer dominates our climate but that other localized drivers will become the main influencers,” she said.
“In particular, we expect the Madden Julian Oscillation (MJO) to move across the Australian tropics, and this will increase cloudiness and precipitation over the coming weeks for northern Australia.
The MJO is a climate engine that circles the equator, encouraging and discouraging tropical precipitation.
When there is an explosion in our region, it leads to an increased risk of low tropical or tropical cyclone activity.
“The precipitation is certainly not over,” said Dr Benger.
How did La Niña go?
This La Niña followed a fairly typical pattern, forming in spring, peaking in summer and breaking down in autumn.
The start was a bit slow, but it certainly ended in style with the flooding of the east coast last week.
It’s too early for a full scientific comparative analysis, but this season certainly fits into the La Niña pattern of causing wet conditions.
As Andrea Taschetto of the University of NSW’s Climate Change Research Center explains, La Niña occurs when there are cool conditions in the eastern Pacific and warm conditions in the west.
The oceans are also intertwined with the atmosphere, bringing enhanced trade winds across the tropical Pacific.
“Because the oceans around the Indonesian seas and seas closer to Australia are warmer than normal, this tends to improve evaporation and humidity from the atmosphere,” she said.
“So generally we see wet conditions associated with La Niña events in Australia, particularly in northern and eastern Australia.”
The Niñas are generally associated with a high number of cyclones – which have not occurred so far this year – but Dr Benger points out that there have been a lot of tropical troughs and that there is still time in the valley. cyclone season.
Then there is all the rain for the last few weeks on the east coast.
Again, it’s too early for a full analysis, but the rainfall and flooding has certainly been epic.
“It’s on track to be in the top five wettest steps on record in New South Wales and the Murray-Darling Basin,” said Dr Benger.
What are the long term trends?
Dr Taschetto said studies suggested that extreme El Niños and extreme La Niñas would tend to appear more frequently in the future as the climate warms.
“It is therefore possible that the impacts associated with El Niños and La Niñas will be stronger in a warming climate,” she said.
There are uncertainties about how El Niños and La Niñas will change in the future, but Dr Taschetto says most climate models indicate El Niños and La Niñas will become more intense.
In addition, the intensity of precipitation is expected to increase as the world warms.
“It’s complicated, but put simply, you just have more moisture in the atmosphere and that can increase the impacts on Australia,” she said.
The Niñas and El Niños do not follow an established pattern.
“A La Niña can develop after a strong El Niño. But if it is a weak El Niño, there is usually no model for having a La Niña afterwards, ”said Dr Taschetto.
There is also no model for an El Niño to develop after a La Niña, so it will be up to the computer models of the forecasting agencies to predict what will happen next.
According to Dr Benger, the climate outlook strongly suggests a neutral ENSO state for the coming months, with this high probability of above average rain in the north.