IOD negative the strongest in 15 years

15 Jul, 2016 02:00 AM
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Harry Hendon, of the Bureau of Meteorology, says an Indian Ocean Dipole negative event has developed over the past couple of months.
Harry Hendon, of the Bureau of Meteorology, says an Indian Ocean Dipole negative event has developed over the past couple of months.

FORGET the potential La Niña event developing in the Pacific Ocean, Bureau of Meteorologist (BOM) climatologists say the newly official negative Indian Ocean Dipole (IOD) has developed into a much stronger pattern.

The Bureau says the negative IOD event, consistent with wetter than average conditions in parts of Australia, is currently at its strongest weekly values in the past 15 years.

Senior principal research scientist with the BOM Harry Hendon told the crowd at last week’s Birchip Cropping Group (BCG) expo that current BOM models suggested the negative IOD pattern will persist and develop through the southern winter and spring.

He said the negative IOD coupled with the chance of a moderate La Niña event developing later in the season, was a key driver in the BOM seasonal outlook for a wetter than average July and August across virtually all sub-tropical Australia.

The tropical Pacific Ocean, the driver of El Niño / La Niña events remains in a neutral state, but Dr Hendon said a large volume of cooler than normal water at depth meant a La Niña could still emerge this year.

Dr Hendon said BOM forecasting tools were forecasting a weak La Niña to develop through late winter and early spring.

However, he said if it did develop, the La Niña would be far weaker than the last event in 2010-11 when there was widespread flooding throughout eastern Australia, which was one of the strongest La Niña events on record.

Dr Hendon said with the coupling of the two climatic events, there was the potential for good spring rainfall.

“The IOD has been the missing piece of the puzzle in recent years, we have not had many full blown IOD negative events this century,” he said.

He said the events were unlikely to trigger the flooding rain of 2010-11.

“Farmers can hope for good spring rainfall with a reasonable amount of confidence, but not as extreme as we witnessed in 2010.”

He said the season had been marked by a rapid transformation.

“We had last year’s El Niño lingering, with high pressure systems over southern Australia, however there was a big change in May and suddenly those high pressure systems were replaced by strong lows, which have been maintained into June and which are helping trigger rainfall.”

FarmOnline
Gregor Heard

Gregor Heard

is the national grains writer for Fairfax Agricultural Media

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