Australia experienced almost as many firestorms - bushfires so intense they create their own weather systems - during the 'Black Summer' season than in the previous three decades.
Firestorms or pyrocumulonimbus events were previously considered to be "bushfire oddities", expert David Bowman told the royal commission into the disaster.
"Unfortunately this last summer there was a near doubling of the record of these events, in one event, and that assembly of data goes back about 30 years," Professor Bowman said, referring to University of NSW research.
"Something happened this last summer which is truly extraordinary because what we would call statistically a black swan event, we saw a flock of black swans.
"That just shouldn't have happened."
Prof Bowman said such events could be associated with extraordinarily destructive fire behaviour, as occurred when the Tasmanian township of Dunalley was almost completely destroyed in 2013.
"People (were) jumping into the sea to save themselves from a true firestorm," he said.
The University of Wollongong's Professor Ross Bradstock said there were multiple pyrocumulonimbus events during the last fire season, particularly on the NSW south coast and into Gippsland in Victoria.
Prof Bradstock said it was an emerging area of fire behaviour science, whereas much of the intent of hazard reduction was focused on the other end of the spectrum.
"The big challenge both for science and managers is to really understand those extraordinary phenomena involved in atmospheric coupling and the limitations that creates for management."
Prof Bowman said in the very worst case, there could be bushfires with totally unpredictable behaviour.
"Eventually you couple the atmosphere to the fire to the landscape and the fire is in a sense becoming dominant.
"It's creating its own weather systems, its own behaviours, and those situations are outside the capacity of science to really predict," he said.
"They're very scary."
The exact number of pyrocumulonimbus events during the 2019/20 season was not stated during Tuesday's hearing of the Royal Commission into National Natural Disaster Arrangements.
In a February media report, UNSW researchers noted that there were about 60 pyrocumulonimbus events in the 30 years after records began in 1998.
UNSW research published last year found climate change was making it likely pyrocumulonimbus bushfires would become more common in parts of southeast Australia.
The firestorms are fires so intense they create their own thunderstorms, extreme winds and lightning.
The devastating 2019-20 bushfires sparked renewed debate about the effectiveness of prescribed or planned burning undertaken ahead of fire seasons.
Senior counsel assisting the commission Dominique Hogan-Doran SC said there is considerable debate about the effectiveness and benefits of different vegetation-related hazard reduction activities.
"It appears common ground that prescribed burns can mitigate but not eliminate the risks associated with bushfire," she said.
"The objective of these burns is to support other risk management measures, including fire suppression, urban planning and building regulations."
Ms Hogan-Doran said a theme from public submissions was the uncertainty and complexity in navigating the bureaucracy when individuals and businesses want to take personal responsibility for managing hazard risk.