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13 January, 2022

La Niña - what is it?

Late November, the Bureau of Meteorology (BoM) declared that a La Niña has developed in the Pacific Ocean.

By Emily Middleton

Flooding has occured at the Castlereagh river a few times over the past couple of months, due to a significant increase in rainfall.

But what exactly is a La Niña? And what does it mean for us?

La Niña is part of a cycle known as the El Niño-Southern Oscillation (ENSO), “a naturally occurring shift in ocean temperatures and weather patterns along the equator in the Pacific Ocean”, according to the BoM.

“During La Niña, waters in the central or eastern tropical Pacific become cooler than normal, persistent south-east to north-westerly winds strengthen in the tropical and equatorial Pacific, and clouds shift to the west, closer to Australia,” said the BoM.

Typically, during La Niña events, rainfall becomes focused in the western tropical Pacific, leading to a wetter than normal period for eastern, northern, and central parts of Australia.

“La Niña also increases the chance of cooler than average daytime temperatures for large parts of Australia and can increase the number of tropical cyclones that form,” said BoM’s head of operational climate services, Dr Andrew Watkins.

“La Niña is also associated with earlier first rains of the northern wet season, as we’ve observed across much of tropical Australia this year. The last significant La Niña was 2010–12. This strong event saw large impacts across Australia, including Australia’s wettest two-year periods on record, and widespread flooding.

“La Niña also occurred during spring and summer of 2020-21. Back-to-back La Niña events are not unusual, with around half of all past events returning for a second year.”

Dr Watkins said that this year’s event is not predicted to be as strong as the 2010-12 event and may even be weaker than in 2020-21 La Niña event.

Essentially, we are looking at having a wetter, and slightly cooler summer than usual.

According to the BoM’s summer outlook, it shows that eastern Australia is likely to be wetter than average, with an increased risk of tropical cyclones, heavy rainfall, and widespread flooding.

There is currently no strong swings to either wetter or drier conditions in South Australia, while parts of Western Australia are likely to see average, to slightly above average rainfall.

It seems like mighty Gilgandra might just miss the full brunt of La Niña, but do expect more than usual rainfall, that’s not going anywhere any time soon.

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