La Nina declared for 2020-21

Intense cyclones and big downpours are on the way with the weather bureau officially forecasting a La Nina event for summer.

Intense cyclones and big downpours are on the summer agenda with a La Nina event to occur this year, the weather bureau declared on Tuesday.

La Nina is a weather phenomenon linked to the shifting pattern of sea surface temperatures through the Pacific and Indian Oceans, which impacts rainfall and temperature variations in Australia. Typically, La Nina is associated with heavier rainfall and increased numbers of tropical cyclones.

On the bright side, a rainier summer means the danger of bushfires decreases. But La Nina has in the past brought devastating storms, including in 2010-12 when Cyclone Yasi thrashed far north Queensland and caused millions of dollars in damage.

Meteorologists believe this summer will bring extreme weather, although of a different kind than last year.

“Generally, it’s the opposite of what we saw last year. We had the hottest and driest year on record, with a drought, devastating bushfires and dust storms coming through,” Sky News Weather channel’s chief meteorologist Tom Saunders said.

“With La Nina though, we can expect higher rainfall, higher risk of flooding, and also a higher risk of tropical cyclones.”

Children play during a flood event in Queensland in 2010. Photo: Mike Knott/NewsMail

BOM analysts who have surveyed international climate models agree La Nina will persist until at least January next year. About half of the models predict it will be a strong event, while others forecast it will be moderate.

“Overall, models do not currently anticipate this event will be as strong as the La Niña of 2010-12, which was one of the four strongest La Niñas on record. The strength of La Niña impacts on Australia are often related to the strength of the event,” BOM officials wrote in the bureau’s latest Climate Driver Update.

During the last La Nina event, which brought on one of Australia’s wettest two-year periods on record, there was an above-average number of severe tropical cyclones, although the cyclone activity overall was relatively normal.

The weather bureau predicts above average rainfall will drench large parts of Australia this spring, while the eastern part of the continent will see heavy showers persist through summer. Cooler daytime temperatures and increased risks of tropical cyclones are also in the cards.

For Australia’s farmers, the increased rainfall so far this year has meant welcome relief from drought. But too much rain at the wrong time could deal another blow to the agricultural industry.

“Farmers love rain, but not when it’s harvest time,” Mr. Saunders said.

The expected increase in summer rain comes against the backdrop of a changing climate that has made Australia about 1.4C warmer since 1910, with a 10 to 20 per cent reduction in autumn and winter rain in the past few decades, according to BOM’s Climate Driver Update.

The US National Oceanic and Atmospheric Administration already declared La Nina conditions were present earlier this month.

La Nina can be considered the inverse of El Nino, and the former event often follows the latter. El Nino is associated with drier weather conditions, as seen during last summer’s extreme bushfire season.