Indian Ocean Dipole weather event that helped cause Black Summer bushfires rapidly forming near Australia
Dipole weather event in the Indian Ocean that contributed to rapid Black Summer bushfires forming near Australia
- Positive dipole formation 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, when combined with El Niño, could have catastrophic consequences.
Ocean and atmosphere measurements 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 say both weather patterns could occur simultaneously this spring, potentially leading to droughts and wildfires.
A positive IOD occurs when cool ocean water rises to the surface, reducing cloud cover, meaning less winter-spring rainfall for central and southeastern Australia.
About 80 percent of people in Australia were affected by the Black Summer Bushfires of 2019, caused in part by a weather pattern now forming. Pictured, German tourists Julia Wasmiller (left) and Jessica Pryor pose for a photo in December 2019
The main factor pointing to a possible bushfire season is the increasing possibility of El Niño and a positive IOD occurring simultaneously, both of which draw rainfall away from Australia
When the IOD index is above 0.4 for eight weeks, a positive IOD year is declared. It currently sits at 0.79, the ABC reported.
It is determined 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 dipole in the Indian Ocean can mean
- Warmer sea surface temperatures in the western Indian Ocean compared to the eastern
- Easterly wind drifts over the Indian Ocean and less cloud cover in northwestern Australia
- Less rainfall over South Australia and the Top End
- If it occurs at the same time as an El Niño pattern, it will prepare the country for a heavy wildfire season
Source: Bureau of Meteorology
The last positive IOD occurred in 2019 and was a major cause of the Black Summer wildfires.
From June 2019 to May 2020, fires burned due to the combination of weather patterns, exceptionally dry conditions and a lack of soil moisture.
The worst fires occurred between December 2019 and January 2020.
Thirty-four people died, but 80 percent of the population was affected by things like poor and even dangerous air quality.
In total, 243,000 square kilometers of forest and woodland burned down and more than 3,000 buildings were destroyed.
Several indicators point to an increase in wildfires over the coming spring and summer.
The main one is the increasing possibility of El Niño and a positive IOP occurring simultaneously, both of which pull rainfall away from Australia.
If this happens, South-East Australia’s lack of winter-spring rains could “prepare the country for heavy summer fire seasons.”
Australia issued an El Niño alert in June, which is still current.
El Niño occurs when sea temperatures in the eastern Pacific become much warmer than average, leading to less rainfall over Australia.
Half of all positive IOPs occur concurrently with El Niño. This last happened in 2015, although it did not cause a major drought or violent wildfires.
But when the patterns occurred in both 2006 and 1982, they caused devastating droughts and fires.
In total, 243,000 square kilometers of forest and woodland burned down and more than 3,000 buildings were destroyed during the devastating 2019-2020 wildfire season
“When El Niño warning criteria have been met in the past, an El Niño event has developed about 70 percent of the time,” the Bureau of Meteorology said in a statement.
In last week’s latest climate driver update, the BoM said higher-than-usual maximum temperatures are highly likely (more than 80 per cent chance) for almost all of Australia.
A negative IOD occurs when warmer waters near Australia produce more cloud cover in the north west of the country and sometimes flooding in the Top End and South Australia.
A negative IOP occurred around this time last year and caused heavy rainfall across much of Australia.