Climate forecasters look at what to expect after three La Ninas

The Bureau of Meteorology is forecasting a higher chance of a drier than average autumn but there is no firm climate driver in place yet correlated with drier conditions.

AFTER three consecutive La Nina events, Australia enters the autumn period without a clear signal of what lies ahead.

But for those looking to the past for a clue as to what lies ahead the odds are for a drier than average year.

Agriculture Victoria climate agronomist Dale Grey told the Birchip Cropping Group trials review day crowd last Friday that after the three last triple La Nina events recorded there had been a drier than average year to follow.

One was an extremely dry season, coinciding with an El Nino and Indian Ocean Dipole positive event, both correlated with dry conditions, one was in the driest 20pc of years and one was a dry-neutral decile 4 season.

Mr Gray said ample soil moisture reserves meant grain growers would be able to cope with a drier than average forecast.

"Given the soil moisture levels something just on the drier side of neutral would likely suit people pretty well," he said.

However, he said there was no scientific rationale as to why the following season after three La Ninas could not be wet.

"There has not been four La Ninas in a row but there is no reason there could not be."

"It is worth noting that even though records for ocean indicators go back to the 19th century we only recorded those triple La Ninas from the 1950s onwards so things do change."

The Bureau of Meteorology three month outlook has a relatively strong likelihood of a drier than average autumn for virtually all of the country and long-term climate models are suggesting El Nino is the most likely possibility this season but Mr Gray said there was no sign in the atmosphere or ocean of a switch in phases happening at present.

This week the Bureau said the La Nina was waning and likely near its end and said most of the models it used were predicting a neutral autumn period.

"There is zero evidence of an El Nino on the way at present, in fact most of the key climate indicators remain more aligned with La Nina conditions as the event slowly breaks down."

"We've still got the sea surface temperatures with warmer waters off Australia, we've still got trade winds favourable for La Nina so while these things do change in time you would be reasonably confident in saying an El Nino is unlikely to form in the short-term, meaning if it does it will be later in the growing season."

In the Indian Ocean he said there was a neutral phase but some signs similar to an IOD negative, while he said the Southern Annular Mode had played a role in shifting rain bearing fronts over summer further south than usual.

The relatively neutral phase at present is in stark contrast to last year, where Mr Grey said three out of the four major influences on climate for south-eastern Australia were in the wet phase.

He said in addition to this there was a massive moisture feed with record warm ocean temperatures to Australia's north.

"By definition, if you have record warm ocean temperatures, you have record evaporation and if you get the right weather triggers to draw the moisture down, you have the chance to get record rainfall which is exactly what we saw in some places last spring."

Looking forward, Mr Grey said farmers could utilise improved BOM climate forecasting tools, such as its Forewarned is Forearmed climate pages.

"The new tools give users extra information on exactly how wet, dry, hot or cold the coming months could be."

"They're really designed to help farmers cope with the risks of extremes, which can be the most damaging thing in a farming system.

"Another benefit is the way they're designed to provide information for the medium term outlook, helping fill that gap between those long-term three month outlooks and the eight-day forecast which is what farmers have been crying out for."

Full article written by Gregor Heard for Farm Online.

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