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.)