When people think about bushfires, the temperature of the oceans don’t always spring to mind. But these sea surface temperatures are one of the biggest culprits in driving the large landscape-scale fires that have been occurring across much of Australia in recent years, like the Black Summer bushfires of 2019/2020.
Burning more than 24 million hectares and impacting an estimated 3 billion animals, the Black Summer was Australia’s worst bushfire season in living memory. Rebuilding the communities and ecosystems affected will take many years.
These devastating fires were caused by years of climate change-induced drought conditions in eastern Australia’s forests and woodlands.
However, the underlying drivers were from sea surface temperatures in the Indian Ocean combined with wind patterns in the Southern Ocean, which fanned strong, dry, westerly winds right throughout spring and summer.
In the case of the Black Summer, the Indian Ocean Dipole (or IOD: the difference in water temperature between the west and east tropical Indian Ocean), was in a positive phase, causing a deep water upwelling of cold water to develop off the north-west coast of Australia and Indonesia. This blocked moisture and rain-bearing clouds from the tropics, priming us for the horrific fire season that unfolded.
(In contrast, when the IOD is in a ‘negative phase’, warm ocean currents spread east across the Indian Ocean, providing more moisture for frontal systems and lows crossing Australia.)
Enter La Niña
I’m pleased to say that it’s been a much kinder fire season over the eastern states of Australia in the last few months.
This is due to the El Niño–Southern Oscillation (ENSO) being in the La Niña phase. During La Niña, a warm body of water sits off the north-east of Australia, leading to above-average rainfall in many areas of eastern and northern Australia.
What was strange about the Black Summer fires is that catastrophic bushfire seasons are typically associated with ENSO being in the El Niño phase, which results in the forests and woodlands of eastern Australia drying out.
The fact that the Black Summer fires occurred despite the absence of El Niño is cause for concern and many scientists have raised the alarm about the potential risks had an El Niño and positive IOD combined last summer as they regularly have in the past.
Bushfire risk remains
On December 2, 2020, before the La Niña rains set in, lightning struck our Carnarvon Station Reserve on Bidjara country in central Queensland.
A bushfire quickly spread through the area, threatening large parts of our reserve as well as the neighbouring Carnarvon National Park and pastoral stations.
Bush Heritage staff mobilised from across QLD and northern NSW and worked closely with fire crews from Queensland Parks and Wildlife Service and the pastoral stations over 12 long days and nights to contain the fire to less than 11,600 hectares or 20% of the reserve.
We managed to stop the bushfire from burning through the important fire-sensitive forest around Fig Tree Spring, home to Canarvon’s famous and majestic White Fig (Ficus virens) tree.
A small crew climbed up the hill with backpack spray units filled with firefighting foam and leaf blowers to put out fires burning in the trees and prevent it spreading in to the spring area.
Sometimes when you stop big old trees like this from burning down, it’s like you can hear the hissing and crackling of the burning wood be silenced by the sweet relief of water and these forest giants living to fight another day.
I could tell from the fluffy juvenile Powerful Owl sheltering in a tree above the spring and staring at me, as well as the Yellow-faced Whipsnake that slithered past my boot that they appreciated our efforts to keep this important ecological refugia unburnt.
Meanwhile further south east, not far from Carnarvon Gorge National Park, a lightning fire that had been burning for weeks was approaching our southern boundary. Our staff worked alongside fire crews from neighbouring Dooloogarah Station to prevent it spreading further north in to our reserve.
Finally, in late December 2020, La Nina arrived properly at Carnarvon and we welcomed the soaking rains originating from the Pacific Ocean to regenerate the landscape once again.
In a positive phase of the Indian Ocean Dipole, a deep water upwelling of cold water develops off north west Australia and Indonesia. This blocks moisture and rain bearing clouds from the tropics from spreading across Australia. 
When ENSO is in a La Niña phase a warm body of water sits off the north east of Australia, leading to above average rainfall in many areas of eastern and northern Australia. 
The ancient White Fig tree (Ficus virens) at Fig Tree Spring on Carnarvon after it was saved by firefighting efforts in December 2020. Photo by Richard Geddes 
Healthy Landscape Manager Central Queensland Chris Wilson briefing fire crews before the night shift on the eastern flank of the fire. Photo by Richard Geddes 
Area burnt by December 2020 fire already regenerating well by late January 2021. Photo by Carnarvon Reserve Manager Chris Wilson 
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