Indian Ocean Dipole weather event that contributed to the rapid formation of Black Summer bushfires near Australia
- Formation of a positive dipole in the Indian Ocean
- The weather pattern reduces rainfall
A weather phenomenon that was a major factor behind the Black Summer bushfires is forming off the coast of Western Australia and could combine with El Niño to produce disastrous effects.
Ocean and atmosphere readings indicate a positive Indian Ocean Dipole (IOD), the Indian Ocean’s version of El Niño.
Australia is already on El Niño alert and some forecasts indicate that the two weather conditions could occur simultaneously this spring, potentially producing drought and bushfires.
A positive IOD occurs when cold ocean water rises to the surface, reducing cloud cover, which means lower winter-spring rainfall for central and southeastern Australia.
Around 80% of people in Australia were affected by the 2019 Black Summer bushfires, partly caused by a forming weather pattern. Pictured are German tourists Julia Wasmiller (left) and Jessica Pryor pose for a photo in December 2019
The main factor indicating a potential bushfire season is the growing possibility of El Niño and a positive IOD occurring at the same time, both pushing rainfall away from Australia.
When the IOD index is greater than 0.4 for eight weeks, a positive IOD year is declared. It is currently at 0.79, the ABC reported.
It is defined by the difference in sea surface temperature between a point in the western Indian Ocean (in the Arabian Sea) and an eastern point south of Indonesia.
What a Positive Indian Ocean Dipole Can Mean
- Warmer sea surface temperatures in the western Indian Ocean compared to the east
- East wind anomalies in the Indian Ocean and less cloudiness in northwest Australia
- Less rainfall over southern Australia and the Top End
- If it occurs at the same time as an El Niño pattern, the earth becomes primed for a severe bushfire season
Source: Bureau of Meteorology
The last positive IOD occurred in 2019 and was a major cause of the Black Summer bushfires.
The fires burned from June 2019 to May 2020 due to a combination of weather, exceptionally dry conditions and a lack of moisture in the ground.
The worst of the fires occurred between December 2019 and January 2020.
Thirty-four people died, but 80% of the population was affected by problems such as poor or even dangerous air quality.
A total of 243,000 square kilometers of bush and forest burned and more than 3,000 buildings were destroyed.
Several indicators point to an increase in bushfire activity next spring and summer.
Most important is the growing possibility of El Niño and a positive IOD occurring at the same time, both pushing rainfall away from Australia.
If that happens, the lack of winter and spring rains in southeastern Australia can “prepare the land for serious summer fire seasons”.
Australia triggered an El Niño alert in June, which is still in effect.
El Niño occurs when sea surface temperatures in the eastern Pacific Ocean become much warmer than average, causing reduced rainfall over Australia.
Half of all positive IODs occur simultaneously with El Niño. The latter occurred in 2015, although it did not produce a major drought or severe bushfires.
But when the two patterns occurred in 2006 and 1982, they produced devastating droughts and fires.
A total of 243,000 square kilometers of bush and forest burned and more than 3,000 buildings were destroyed during the devastating 2019-2020 bushfire season
“When El Niño warning criteria have been met in the past, an El Niño event has developed about 70% of the time,” the Bureau of Meteorology said in a statement.
In its latest Climate Factors Update last week, the BoM said higher than usual maximum temperatures are very likely (over 80% chance) for almost all of Australia.
A negative IOD occurs when warmer waters near Australia produce more cloud in the northwest of the country, and occasional flooding in the Top End and South Australia.
A negative IOD occurred around this time last year producing heavy rain for much of Australia.