BOM declares negative Indian Ocean Dipole

Tyne Logan
Swellnet Dispatch

The climate phenomenon that brought Australia one of its wettest winters has been officially declared for this year.

Bureau of Meteorology experts have announced that the Indian Ocean Dipole (IOD) is in a negative phase for the first time in five years.

Every event is different, but a negative phase usually brings wet conditions to regions from Western Australia's Gascoyne down and across to Tasmania.

The last time a negative dipole event was declared was in 2016, between June and September.

That winter was the second wettest on record, with more than half of Australia receiving rainfall totals in the highest 10 per cent of historical records for the June to August period.

May to September was also the wettest on record.

Bureau of Meteorology senior climatologist Felicity Gamble said this year was not expected to be as strong as the last event.

"So while the strength of this years event is expected to be weaker than our last negative IOD in 2016, significant events can still occur and it's important to keep up to date with our latest climate updates and forecasts," she said.

A negative phase of the IOD can increase rainfall across parts of Australia.(Supplied: Bureau of Meteorology)

What could it mean for farmers?

North-west of Wagga in the Riverina, New South Wales agronomist and farmer Rohan Brill is happy with how the season is shaping up so far.

"We are in the middle of July and crops have a good bank of soil moisture underneath them, which is what we always hope for, really — so that's a good thing," he said.

But 100 kilometres north, in the state's lower Central West, conditions are already quite wet.

"If it came in with a fairly wet period from now on I think some of that area would suffer a bit of damage," Mr Brill said.

Wet years can lead to extra fungal issues, nitrogen depletion and smothered crops, but for the most part they are welcome.

"A year like 2016, some people suffered, but overall they're still usually big years," Mr Brill said.

Large parts of the country have had above average rainfall so far this year, but many would still welcome more rain (Supplied: Bureau of Meteorology)

'Amazing, really'

Negative dipole years typically bring wetter than average conditions to the Gascoyne, Pilbara and Goldfields regions of WA.

Any additional rain over the next four months will be seen as a bonus for farmers in those areas and could lead to a record wet year.

Caroline Thomas, who runs Marron Station near Carnavon with her husband Simon, said their average annual rainfall had already doubled.

"We haven't even finished the year yet — it's amazing, really," she said.

"As much as you can it's a good time to be building up number and trying to make the most of the feed, really.

"It's very green, it looks like farmland — and the animals, they're pretty relaxed.

"They go out to feed until about morning tea and then lay around all afternoon because they are full."

Will negative events get more common?

Research has showed extreme, positive dipole phases, like that of 2019, could be more frequent in future.

But Australian National University climate scientist Nerilie Abrams said the future frequency of negative events were more difficult to predict.

"There's an interplay between the overall warming of the ocean and what's happening with the variability of the Indian Ocean Dipole," she said.

"Climate models would tell us we expect the negative events to become less common.

"But at the same time we know that the ocean is warming because of global warming, so there's a balancing of those two different effects that will ultimately determine what the impact on the Australian landscape is."

IOD events occur in the cooler months of the year and generally break down as summer weather patterns establish over the Indian Ocean.

// TYNE LOGAN and KATE DOYLE
© Australian Broadcasting Corporation. All rights reserved.

Comments

NDC's picture
NDC's picture
NDC Wednesday, 21 Jul 2021 at 2:45pm

Was it a negative IOD that resulted in the iffy season in the Ment's a few years back
Where people said there was a lot of unfavourable winds and surprisingly cool water
???

Craig's picture
Craig's picture
Craig Wednesday, 21 Jul 2021 at 3:13pm

Yep, that was a record + event that brought strong S/SE-SE trades and cold upwelling..

https://www.swellnet.com/news/swellnet-analysis/2019/10/31/shivering-in-sumatra

Blowin's picture
Blowin's picture
Blowin Wednesday, 21 Jul 2021 at 4:26pm

Ahhhhh…..good times. Sniff sniff ( wipes tears).

indo-dreaming's picture
indo-dreaming's picture
indo-dreaming Thursday, 22 Jul 2021 at 10:37am

So if this negative IOD event is for now, the reality is the winds in Sumatra havent been set in a South wind pattern, it looks to me to be a very normal year mix of wind directions and strengths plenty of NW-W winds and then some south and east winds in the mix..

Thats not like a bad year, like 2019 that as soon as you get to about late May it blows South-SE pretty much everyday and any changes in direction are generally for a few hours or a day not days.

I cant see Aussies going to Indo next year, would be good if it was a bad year for winds in 2022 so less chance of bad winds in 2023 which is most likely going to be crazy crazy crowded.

freeride76's picture
freeride76's picture
freeride76 Wednesday, 21 Jul 2021 at 2:51pm

nope. pos .

davetherave's picture
davetherave's picture
davetherave Wednesday, 21 Jul 2021 at 4:03pm

Wasn't our recent LA Nina combined with negative iod?

Craig's picture
Craig's picture
Craig Wednesday, 21 Jul 2021 at 4:15pm

Not quite, close though. They usually are though.

Here's the record of the last two years. Just didn't reach the threshold.

This is the DMI index which is slightly different but also takes into account the wind anomalies along with the temperature anomalies. https://stateoftheocean.osmc.noaa.gov/sur/ind/dmi.php

Redmond Clement's picture
Redmond Clement's picture
Redmond Clement Wednesday, 21 Jul 2021 at 6:09pm

Good for the locusts and mozzies.

oxrox's picture
oxrox's picture
oxrox Wednesday, 21 Jul 2021 at 8:33pm

2019 was a positive IOD not negative. I was in Sumatra and froze in the water. Means less rain for Australia, Also the sudden stratospheric warming and another weather event as well for that year made Oz incredibly dry hence the bushfires on the east coast.

Craig's picture
Craig's picture
Craig Wednesday, 21 Jul 2021 at 8:50pm

Negative SAM was the other factor brought on by the Sudden Stratospheric Warming Event. 

palmymick's picture
palmymick's picture
palmymick Thursday, 22 Jul 2021 at 8:02pm

Doesn't negative IOD combined with negative SAM mean good snow falls?
Not that it will matter with bloody lock downs

Craig's picture
Craig's picture
Craig Thursday, 22 Jul 2021 at 9:17pm

Yes but we still need the Long Wave Trough focussed across the south-east of the country, bringing the fronts up across the mountains. No use if it's over near WA.

palmymick's picture
palmymick's picture
palmymick Monday, 26 Jul 2021 at 7:36pm

Gotcha. So the southern storm tracks needs to get active and carry the storms from WA past Oz and over to NZ bro. And if the SAM is negative the storms are further north and Oz gets the goods but if the SAM is positive, the storm track is further south and NZ gets the goods or we miss out altogether

tango's picture
tango's picture
tango Thursday, 22 Jul 2021 at 1:40pm

And the winds were too south too often late in the season....though we did get a couple of truly mental days.....

Hutchy 19's picture
Hutchy 19's picture
Hutchy 19 Thursday, 22 Jul 2021 at 4:14pm

Great work Craig ! Really enjoy your work on these macro weather issues . BOM seems late ( as usual ) to register we have had a wet winter especially in WA . Learnt from you that La Nina's have a 50% probability of happening twice . Bought Select Harvest shares ( almond grower ) as thought SW USA would have a drought which would negatively affect this years almond crop . Gave me even more confidence that next years crop could also be affected .
Can you give any more information of how/if the IOD relates to La Nina / El Nino ?