Australia should brace for flooding this storm season with the bureau of meteorology (Bom) predicting there is double the chance of a La Niña forming.
La Niña events increase the chances of above-average rainfall for northern and eastern Australia during spring and summer. Bom climatologist Tamika Tihema says the bureau has predicted there is double the chance of La Niña forming after updates to it current modelling.
“This doesn’t guarantee that a La Niña will occur, but that there is around a 50% chance of La Niña forming. This means roughly half the climate models the bureau uses suggest that a La Niña event is likely to develop,” she says.
Tihema says the possibility of La Niña influencing severe weather, with higher than average rainfall predicted for the eastern two-thirds of the country for the rest of the year, has increased the risk of flooding.
“For many areas, including parts of eastern New South Wales, eastern Victoria, northern Tasmania and south-west Western Australia, and northern Australia, the soil moisture is wetter than average,” she says.
“As this will mean more rain on wet soils, there’s an increased risk of flooding in these areas.”
Tihema says the increased chance of La Niña is partially attributed to sea surface temperatures in the central tropical Pacific Ocean which have cooled over the past two months.
“We are seeing changes in both observations and the climate model outlooks that indicate an increased chance of La Niña in the coming months,” she says.
“Chances of exceeding the median rainfall is greater than 70% for much of the eastern two-thirds of the country for the rest of 2021.
“The chances of above median rainfall for the November to January period is around 60% or more for the eastern two-thirds of Australia.”
NSW SES commissioner Carlene York says this year’s storm season – which traditionally runs from October to March – is likely to bring similar conditions to last year, including widespread heavy rain and the risk of riverine and flash flooding.
“During the previous storm season, we experienced major floods right across the state,” York says.
“It wasn’t long ago our volunteers responded to the major flooding event that overwhelmed communities across the Hawkesbury-Nepean, Hunter and mid-north coast. That event alone saw us respond to more than 14,000 requests for assistance, including more than 1,000 flood rescues.
“It is incredibly important communities make sure they are ready. Storms can happen at any time. The more you can do now to prepare, the less likely you’ll end up needing emergency assistance from our volunteers when these weather events hit.”
York says Covid-safe practices had been implemented to respond to lockdowns and ongoing health measures.
The BOM says while El Niño-Southern Oscillation (ENSO) is a “naturally occurring” part of the climate system, climate change continues to have an impact on changing weather patterns. Australia has warmed by 1.44C since records began in 1910.
Southern Australia has seen a reduction in rainfall of between 10 and 20% during its cool season in recent decades, while rainfall across northern Australia during its wet season has increased since the 1990s, with shorter and heavy showers becoming more frequent.
“Research suggests El Niño may bring heavier rainfall over the central and eastern tropical Pacific Ocean under global warming, and La Niña rainfall may be heavier in the western Pacific and over the South Pacific … but what these changes mean for Australia is unclear,” Tihema says.
“Research also suggests that there might be an increase in the frequency of large El Niño and La Niña events. What the future holds for El Niño, La Niña, and their impacts are the subject of current research.”