What is La Niña, and how will it impact Australia this summer?

By Donna Lu and Peter Hannam

What is La Niña?

The Australian Bureau of Meteorology has declared a La Niña weather event, with modelling predicting it “will persist until the late southern hemisphere summer or early autumn 2022”.

What is La Niña?

During a La Niña event, strong trade winds blow west across the Pacific Ocean, pushing warm surface water towards Asia and the seas north of Australia.

The warmer waters lead to increased rainfall across northern and eastern Australia.
The warmer waters lead to increased rainfall across northern and eastern Australia.

How often does La Niña occur?

Australia also experienced a La Niña weather event last summer, making it the first time back-to-back events have occurred in a decade – since 2010-11 and 2011-12.

But it isn’t that uncommon for multi-year La Niña events to occur, according to BoM. For example, La Niña affected three consecutive years from autumn 1998 to autumn 2001.

How often does La Niña occur?

According to BoM, the six wettest winter-to-spring periods recorded in eastern Australia have all occurred during La Niña years.

Last summer was the coolest summer in nine years and wettest in four years, with 29% more rain than average.

What does it mean for this summer?

The current La Niña may also be weaker than the one last summer. However, insurers are still preparing for a busy season. Soils are far more saturated than last year, and any dams are close to or at capacity.

Tropical cyclones are also more likely. The bureau estimates there is a two-in-three chance Australia will have more than the seasonal average of 11 cyclones in its region.

What does it mean for this summer?

Dr Agus Santoso, a senior research associate at UNSW’s Climate Change Research Centre, says climate change also affects La Niña events.

“Particularly if you get warmer sea surface temperatures surrounding Australia, that can enhance convective activities that can produce storms,” he said.

What about
climate change?

A recent review Santoso co-authored concluded that the frequency of El Niño and La Niña events would increase under business-as-usual scenarios of greenhouse gas emissions.

Unless emissions are reduced, El Niño and La Niña events are projected to increase from 5.6 events a century in the present to 8.9 and 8.3 events a century in future, respectively.

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