Last year’s fire season was “unmatched” because 2019 was the hottest and driest year on record, a study of factors behind the Black Summer bushfires found.
The study warns horror fire seasons are likely to continue as well as “rapidly intensify” because of climate change.
More fires and more intense fires are predicted to become a feature of southeast Australia, lead author Nerilie Abram from the Australian National University said.
The Black Summer bushfires were in many respects the worst Australia has seen.
But Professor Abram said we could expect to see “catastrophic” bushfires that would be “beyond anything we had experienced in the past” as current climate trends continued.
WHY BUSHFIRES ARE GETTING WORSE
Professor Abram said there was no “single factor” that caused worse fires in a changing climate.
The increase of carbon dioxide and other gases in the atmosphere causes “multiple climatic influences”, including hotter temperatures, less rain, drier soil, heavier winds, and extreme and sudden changes in the weather.
So far, the climate has warmed one degree since before industrialisation and the mass uptake of burning coal.
But in southeast Australia in 2019 it was two degrees warmer than the historical mean temperature, Professor Abram said.
Temperatures in Australia could be as much as seven degrees on average above pre-industrial levels before the end of this century if emissions were not reduced, she said.
“Numerous extreme heat records were broken in Australia in 2019, including the warmest national average daily temperature ever recorded of 41.9 degrees on December 18,” she said.
“The annual mean rainfall for 2019 was the lowest on record when averaged across southeast Australia.
“December 2019 also had the driest fuel load on record in southeast Australia.”
She said the conditions that caused the Black Summer fires were a combination of human-caused climate change and traditional variability in heat and dryness.
A normal weather pattern called an Indian Ocean Dipole, as well as conditions over the Southern Ocean, contributed to the hot and dry conditions in 2019.
That pattern has “historically been associated with droughts and major forest fires in Victoria”.
What climate change effects did was “compound” these natural weather patterns to make fire seasons that would normally be bad even worse, she said.
“Human-caused climate change is now altering the behaviour of the drivers of interannual climate variability,” she said.
A horror bushfire season did not occur in the 2020/21 summer because of the natural La Nina weather conditions taking place.
La Nina refers to an unusually wet and cold spring and summer, caused by a build-up of cold water in the tropical Pacific accompanied by strong winds.
“We don’t expect every summer to be like 2019/20 – and this La Nina year is a good example of that,” Professor Abram said.
“But we can’t look at climate change as something in our future.
“Our new work highlights the strong evidence that southeast Australia’s climate has shifted and that this type of fire weather is becoming more frequent, prolonged and severe.”
COUNTING LOSSES FROM HORROR FIRE SEASON
Nearly a quarter of temperate forests in NSW, Victoria and the ACT burned last fire season, the study noted.
There were 33 deaths and more than 3000 homes were destroyed in regional areas.
Indirect deaths from smoke haze numbered an estimated 417 Australians, with 3151 hospitalisations.
There were also an unprecedented number of “violent pyroconvective storms”, Professor Abram said — thunderstorms generated by the extreme conditions of megafires.
The study notes that in NSW, 37 per cent of the state’s rainforest burned — an environment that is not adapted to fire and where major blazes are not usually able to gain a footing.
“In economic terms, the Black Summer fires are expected to be Australia’s costliest natural disaster to date,” she said.
“The combination of climate variability and long-term climate trends generated the climate extremes experienced in 2019.
“(The year) was characterised by exceptionally dry fuel loads that primed the landscape to burn.”
The study noted there were predictions more than 10 years ago that the impact of climate change would cause “directly observable” increased fire risk by 2020.
Those predictions “have indeed eventuated”.
The ANU study team included researchers from the ARC Centre of Excellence for Climate Extremes and bushfire experts from the NSW Bushfire Risk Management Research Hub.