Wetter than usual summer expected as La Niña declared

24 November 2021

Large parts of northern and eastern Australia have been experiencing significant weather events over the past few weeks and now they can be partly attributed to the developing La Niña.

The Australian Bureau of Meteorology (BOM) declared a La Niña on Tuesday (23 November) which will see above average rainfall across much of northern and eastern Australia as we head into summer.

CQUniversity Adjunct Professor of Environmental Geography' Steve Turton' said the declaration by BOM meant that those living in northern and eastern Australia could expect to see an increased chance of widespread rainfall and flooding this season.

"We need to keep in mind' that several other climatic drivers affect our weather from year-to-year'" Professor Turton explained.

"These include the El Niño-Southern Oscillation (ENSO)' the Indian Ocean Dipole (IOD) and the Southern Annular Mode (SAM). ENSO and IOD are most important for tropical and sub-tropical areas of Australia' while SAM largely influences southern parts of the country."

Professor Turton' who will soon release a book titled Climate-resilient development pathways and opportunities in the Anthropocene: Australian perspectives and solutions said El Ni̱o and La Ni̱a were opposite phases of a natural Рbut powerful Рclimate phenomenon across the tropical Pacific Ocean that swing back and forth with an average periodicity of three to seven years.

"The last La Niña was 2020-21' so not long ago' however the last significant La Niña was 2010-12 and that saw the Brisbane and Rockhampton floods and Cyclone Yasi in far North Queensland'" Professor Turton said.

"The strongest La Niña in history was the 1973-74 event that is still Australia's wettest year on record. The devastating Brisbane floods of February 1893' January 1974 and January 2011 were all associated with strong La Niña events."

Professor Turton said this week's La Niña declaration also meant an increased risk in cyclone activity for the season.

"This La Niña is shaping up to be weaker than the moderate 2020-21 event and much weaker than the strong 2010-12 event'" Professor Turton assured.

"This event is likely to only last until early February. Meanwhile' a developing positive phase in the IOD will counteract the La Niña to some extent ahead of the monsoon wet season kicking in around Christmas time."

Professor Turton said the La Niña and its opposite El Niño could be affected by climate change as the world continues to warm.

"The latest global assessments (IPCC 2021) show that it is very likely that the amplitude of ENSO rainfall variability will intensify in response to global warming this century'" he said.

"This means extreme weather events will be more pronounced if El Niños and La Niñas increase in frequency and strength' meaning increased risk for droughts' intense heatwaves' bushfires and floods for most of eastern and southern Australia. So not good news."