After several years of drought and blazing summers, Australia has officially entered a La Niña weather pattern.
The good news is that we may be spared the catastrophic bushfires of summers past.
But with Australia already experiencing its wettest spring in years, there are fears that pattern could persist through to the end of January, and possibly the whole summer.
So as El Niño makes way for La Niña, here’s what you need to know.
What is La Niña?
As Bureau of Meteorology head of operational climate services Andrew Watkins explains, La Niña is a result of a change in ocean temperatures in the Pacific Ocean.
As the water gets cooler near South America and warmer near Australia, weather patterns also change, moving cloud and rainfall towards Australia.
It will bring wet conditions through northern, eastern and central Australia.
What does that mean for us?
As much of Australia has already experienced, La Niña means rain, and lots of it.
“We tend to get more rainfall across northern and eastern Australia over the coming summer months,” Dr Watkins said.
Spring and summer will be wetter than usual, and colder too, particularly in the eastern and southern parts of the country.
Will it bring extreme weather events?
During La Niña, parts of the country are likely to see an increased risk of tropical cyclones and flooding.
Professor Matthew England of the University of NSW Climate Change Research Centre told The New Daily that while we cannot say there will definitely be flooding events – because the atmosphere is unpredictable – risk factors do increase during La Niña.
“The most catastrophic floods have always tended to occur during La Niña events, for the eastern seaboard, Queensland and New South Wales especially,” Professor England said.
“That’s not to say we’ll necessarily get them.”
Professor England said La Niña could herald a cooler summer, free from bushfires and heat extremes, along with some much-needed drought relief for farmers.
“It could make for a mild and benign summer in terms of extremes, but it could also lead to some heavy rainfall events,” he said.
The areas most likely to be hit by heavy rainfall and flooding during the next three months include Queensland, NSW, Victoria and Tasmania.
Because conditions have been wet through winter and spring, Dr Watkins said the risk of flooding is heightened this year.
With wet soils, full rivers and high catchments – more rainfall brings the risk of widespread flooding, particularly in south-east Australia, he said.
The chance of tropical cyclones occurring, as well as their severity, increases during La Niña periods, particularly in Queensland, Professor England said.
But the Bureau of Meteorology is generally able to give accurate warnings four to five days before a cyclone hits, he said, giving people time to follow evacuation orders.
What about heatwaves and bushfires?
During La Niña, heatwaves are less extreme.
But they are also longer and more humid, and still pose a risk of heat stress for some people.
In some good news, Australia is less likely to see bushfires over spring and summer.
The wetter conditions will reduce the risk of fires like the ones we’ve seen in recent years, but there could be an increased risk of grass fires as new vegetation dries over summer, Dr Watkins said.
How do we prepare?
Professor England said it is enough to heed the advice of the Bureau of Meteorology, which is generally able to provide fair warning and alerts.
He also said it was a good time to do things like repair roof leaks and other preparation for heavy rainfall, and to put a plan in place in case you do need to evacuate.
Why is it already wet and cold?
The La Niña was only announced on Tuesday, but Australia has already been experiencing wet and cool conditions.
Dr Watkins said it could be “our coolest spring since 1999 and it is looking like the wettest spring since 2011”.
La Niña reinforces those conditions, he said, but is not the only reason for them.
“We have seen a number of climate drivers pushing us towards wetter conditions,” he said.
Those include a negative Indian Ocean Dipole, while weather systems have also been pushed further south by conditions over Antarctica, and warmer waters around northern Australia.
How is it different to other years?
The last significant La Niña hit Australia from 2010 to 2012, leading to the nation’s wettest two years on record, with widespread flooding.
However, Dr Watkins said this year’s event was not predicted to be as strong.
“Last year we saw a weak-to-moderate La Niña event. Now we’re backing that up with a weaker La Niña event,” he said.
“A weak La Niña can still bring heavy rainfall at times. With a wet landscape we are at risk of more widespread flooding over the summer.”
Climate Council head of research Simon Bradshaw said climate change is another factor that cannot be overlooked.
“All today’s weather is occurring in an atmosphere that is warmer, wetter and more energetic due to climate change, driven by the burning of coal, oil and gas,” Dr Bradshaw said in a statement.
“With climate change, we are tending to get more of our rain in the form of heavy downpours, increasing the risk of dangerous flooding.”