Where is the ‘promised’ El Niño drought?

Vic Drought Hub - Farmland 1

Wednesday 31 January, 2024

After September’s El Niño declaration, the drier times many anticipated didn’t occur – so what happened?

 

On 19 September last year, the Bureau of Meteorology (BoM) declared an El Niño event. It followed several months in the “neutral” phase, after the three-year La Niña occurrence was declared finished on 10 March 2023.

Thunderstorm with lightning bolts over paddock what happened to El Nino

Professor Michael Tausz, Director of the Victoria Drought Resilience Adoption & Innovation Hub, said, “Once the El Niño–Southern Oscillation, or ENSO, switched to the El Niño condition, many farmers were expecting – and preparing for – potentially drier conditions across much of Australia.

“Back in September, the Vic Hub emphasised the move into an uncertain stage, where it is unclear how the season will develop. Although El Niño is often perceived to be directly associated with droughts, the BoM emphasises that ENSO is only one of several climate drivers that are used in the Bureau’s sophisticated forecast models – and it’s not necessarily a decisive one.”

Prof Tausz said rather than basing any expectation of seasonal conditions just on an El Niño declaration, the Vic Hub, which is funded by the Australian Government’s Future Drought Fund, regularly points to the long-range forecasts issued by the BoM, which take into account and model the effects of all known climate drivers – not only El Niño.

“In September and early November, these forecasts also reported only a 20-40% chance of exceeding median rainfall in most of Victoria for the next three months.

“Perhaps not surprisingly, farmers and others in the community were scathing about the ‘unreliable forecasts’, and some went as far as blaming BoM for what turned out to be in hindsight poor business decisions, such as destocking.”

 

Is such criticism justified?

 

Prof Tausz said the ensuing issues of long-range forecasts soon moved to predicting at least a 50% chance of rainfall exceeding three-month rainfall medians in much of Victoria.

El Nino gauge BoM 2024 0130
El Niño gauge, 31 January 2024, Bureau of Meterology

“Putting aside that some of the fiercest criticism ignored these updates, there seems to be also a fundamental misunderstanding in how these longer-range forecasts should be read. Because of the highly complex and chaotic system that is our atmosphere, it is currently still impossible to make direct weather predictions for more than a few days ahead. Longer-range forecasts are therefore expressed as likelihoods of a certain condition. For example, the latest BoM forecast from 25 January gives a 30-60% chance of exceeding the median rainfall in Victoria.

“As an example, a 30% chance of exceeding median rainfall – as given for Victoria’s south-western corner – should be read as follows: if we make the prediction of above-median rainfall 10 times, we would get it right only three times: the 30% chance is three out of 10 predictions.

“In other words, if we predict below-median rainfall, it would be correct seven out of 10 times. Above-median rainfall has shorter-than-even odds, but is certainly not impossible, and should definitely not be completely discarded in any planning.”

Prof Tausz said the “correctness” of such a forecast cannot be evaluated in a single season, but only over the longer term, once such a forecast is issued multiple times.

“This may not alleviate frustrations about management decisions being made in this particular season, which would have been different in hindsight, but using the guidance consequently and appropriately as one input for risk management over multiple seasons will be beneficial in the mid to longer term.”

 

Cows grazing rural Victoria

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Media Contact

Samantha Schelling, Communications Officer
Victoria Drought Resilience Adoption & Innovation Hub
samantha.schelling@unimelb.edu.au | mobile: 0403 106 404