EXPERT REACTION: BOM has declared 70% chance of a 3rd consecutive La Niña year

• BoM’s forecast now fits nicely into what other main international climate forecast and warning services are providing (eg US Government Climate Prediction Center/NOAA; the World Meteorological Organisation, etc) (see the attached for the latest output from the US Government on this La Niña!).
• Interestingly, these other world agencies have simply maintained La Niña’s continued existence throughout the past months and years.
• Most La Niña events cease sometime during our Southern Hemisphere autumn (which means autumn 2023 is now likely to see the end of this event).
• This La Niña is an example of a somewhat rare – but not unprecedented  - ‘protracted La Niña event’. This event follows a quite intense (and drought-producing) El Nino event through 2018/2019 which led to Australia’s severe bushfire period during that time.
• We know that severe, drought-inducing El Niño’s are very often followed by intense or protracted La Nina’s – so Australia should have been prepared for this period of back-to-back severe seasonal climate patterns of extreme drought and extreme flood.  
• Meanwhile, we know very little of the likely impact of anthropogenic climate change on La Niña  - or El Niño (collectively known as ENSO). Will they become more severe? Will they become more frequent? We don’t know. This is despite the fact that Australia, and especially eastern Australia, is one of the most vulnerable regions on the globe in regards to the direct impacts of La Nina or El Nino (or its subtle variations). There is but one standout scientific paper on climate change and ENSO and that is by Wenju Cai in CSIRO.
• To add to this nice complexity, El Niño and La Niña are produced/develop in the tropical (equatorial) Pacific Ocean – especially in the central Pacific and across to the South American Coast (hence their Spanish names). Australian greenhouse gases have little direct impact on El Nino and La Nina – yet, ironically, Australia is subject to most of El Niño and La Niña’s impacts.      

The probability that a La Niña may re-emerge in summer has increased from 50-60% in the past months to about 70%, thus an increased chance for a third La Niña since 2020.  A triple La Niña is quite rare in the historical record.
 
This elevated likelihood is concurrent with the development of negative Indian Ocean Dipole (IOD). A negative IOD, marked by warming northwest of Australia and over Indonesia, can enhance La Niña development through strengthening the Pacific trade winds that support a La Niña. 
 
The negative IOD, expected to peak in spring, will likely bring higher-than-normal rainfall across the southern parts of Australia, including NSW and Victoria in the coming months. This is in addition to the prospect for the triple La Niña and the backdrop of already saturated catchments.

La Niña usually lasts for 2-4 years before switching to an El Niño phase (3-5+yrs). The two events however are non-linear, meaning we are likely to experience severe drought conditions for longer during El Niño. The third wave of La Niña does not guarantee we will see floods again.

While the focus is mostly on climate change (caused by human activity), we need further research into climate variation which is caused by changes in the ocean temperatures resulting in swings in climate patterns like La Niña and El Niño. Better observations of ocean temperatures will help in predicting these events and help in preparing for floods and droughts.

The Australian Government should continue to fund research undertaken by CSIRO’s Ocean and Atmosphere division. Australia has experienced more droughts than floods so the BOM announcement should not be taken as an alarm bell.

Naturally, with the devasting floods in recent times, Australians in flood-prone areas would be edgy. We need to build new dams on the East Coast, so water is captured during La Niña phases and use this water during the El Niño phase. The West Coast of the American continent is likely to experience further drought conditions if La Niña persists.

A third La Nina in as many years is very concerning for its potential for wet conditions over eastern Australia this spring. Many regions are still recovering from flooding events earlier this year and additional rainfall in already saturated catchment areas could impede this recovery. While a triple dip La Nina is not unprecedented, it has only occurred three times since 1950. La Nina events impact the weather and climate across the world, with increased likelihood of drought in California and wet conditions in south-east Asia and typically leading to cooler global temperatures. Despite this, global temperatures during the 2020s have still remained over 1 degree warmer than the pre-industrial period, indicating the overwhelming influence of human influence on the climate and the urgent need to reduce emissions.