La Nina 2021 weather event declared for Australia’s summer
Australia’s Bureau of Meteorology has declared a La Niña weather event is under way in the Pacific, bringing the country in line with other agencies, and underscoring the prospect of a relatively cool, damp and stormy summer for much of the north and east.
The declaration, made at a media conference in Melbourne on Tuesday, confirmed a Guardian Australia report. The bureau said it had shifted its outlook for La Niña on its main climate drivers forecast.
“Key atmospheric and oceanic indicators of the El Niño-Southern Oscillation (ENSO) show an established La Niña,” the bureau said.
It made the call based on sea-surface temperatures that were close to La Niña thresholds in a key region of the tropical Pacific, with models indicating further cooling was likely. The indicators they watch include the amount of cloud buildup and the strength of trade winds.
“The current model outlooks suggest this La Niña will persist until the late southern hemisphere summer or early autumn 2022,” the bureau said, extending the longevity of the event from earlier predictions that it would begin to dissipate by the end of January.
A majority of the models used by the bureau now predict La thresholds will be met by February 2022.
Andrew Watkins, head of the bureau’s Operational Climate Services, said the La Niña would also increase the likelihood of cooler than average daytime temperatures for large parts of Australia. “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,” Watkins said. 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, he said.
One difference compared with a year ago, however, is that soils are far more saturated, and many dams are close to or at full capacity.
The declaration came a day after the bureau confirmed the season’s first tropical cyclone had formed in the Australian region.
Cyclone Paddy developed near Christmas Island and reached category one stretch on Monday but will weaken by Wednesday without making landfall.
A declaration of a La Niña coincided with the bureau’s fortnightly update of the main climate drivers for Australia’s weather on Tuesday afternoon. It has had a La Niña alert in place for weeks. It also issued warnings of some flooding to come from rains later this week reaching eastern Australia.
“You can see the pattern is already La Niña and you can see the impacts,” said Agus Santoso, a senior research associate at UNSW’s Climate Change Research Centre, ahead of the declaration. “It’s not strong but it’s not that weak either.”
People living in eastern Australia, in particular, hardly need more confirmation that conditions have recently turned wet and cool. While the aboveaverage rainfall endured by many areas during winter and spring had more to do with conditions in the Indian Ocean, the Pacific tends to have more influence in summer.
During La Niña years, the east to west trade winds blowing across the equatorial Pacific strengthen. These effectively push rain systems westwards and raise the chance of flooding, and also lift relative sea level in the western Pacific.
Such years also tend to have more cyclones than usual. Last month, the bureau estimated there was a two-inthree chance Australia’s region would have more than the seasonal average of 11.
Last year also included a La Niña and experts say there is about a 40% chance of having back-to-back events. The last double bout covered 2010-11 and 2011-12.
“I suspect it will be neutral next year,” Santoso said, adding “it’s not impossible to have three years in a row” as shown by the 1998-2000 period.
Ben Domensino, a senior forecaster at Weatherzone, noted the US National Oceanic and Atmospheric Administration (Noaa) declared a double-dip La Niña last month. It uses a lower threshold to assess such an event, or its opposite, an El Niño.
“Although it’s not technically been declared [in Australia], we’ve been in a very La Niña-like state for some weeks now,” Domenino said, also ahead of the declaration.
Recent widespread and heavy falls have resulted in minor to moderate flooding in many inland rivers, notably in NSW. The Lachlan River, which last week threatened the NSW central west town of Forbes, remains at major flood levels in places.
Another belt of rainfall – with moisture fed in part from Cyclone Paddy – is heading eastwards. That should bring 40-60mm of rain to a large area from Queensland into Victoria, with isolated falls of 100mm. Since catchments are already saturated, more flood watches will be issued, Domensino said.
Farmers struggling to get crops in before fields become saturated are among those looking to the skies for relief from the rain. Insurers too will be watching closely since flood damage typically exceeds that from droughts and even bushfires.
During the most recent La Niña and its aftermath from December 2020 to April 2021, the Insurance Council of Australia declared three catastrophes. These triggered about 65,000 insurance claims for damages totalling just over $1b, the ICA said.