Last updated February 8, 2019 at 9:49 am
The shape of a bushfire, not just its intensity, determines whether it will become a catastrophic firestorm, say researchers.
Facing another potentially catastrophic summer of bushfires, Australian scientists have been able to predict what makes a bushfire develop into a ‘nightmare’ firestorm.
Contrary to previous work which pointed the finger solely at the energy of the bushfire, the team from the University of New South Wales and the ACT Emergency Services found the shape of the fire as a vital factor.
Firestorms are a nightmare scenario for firefighters.
Unlike typical bushfires, which spread across the landscape with well-defined fronts, firestorms are created by intense bushfires that create their own weather systems. The intensity and heat of the fire creates a fast-rising plume of hot air above the fire, which then draws air from the area surrounding the fire towards it in gale-force winds.
With this constant supply of inrushing air the fire intensifies to extreme temperatures, and the hot air rises into the upper atmosphere where it cools and condenses into a plume of cloud called a pyrocumulonimbus cloud extending 10-15km in altitude.
At these altitudes the bushfire plumes can develop their own thunderstorms, with lightning spreading the fire in multiple, unpredictable directions.
The conditions leading to firestorms can also result in fire tornadoes.
“The most dangerous” type of bushfire
“Thunderstorms generated by the heat from a fire are the most dangerous manifestation of a bushfire,” says Rachel Badlan, who worked on the research at UNSW Canberra and presented the work at the recent Fresh Science competition.
“These firestorms create their own weather with lightning, strong winds, and even tornadoes that spread fire in multiple directions. These ingredients make them impossible for firefighters to put out.”
These conditions are common in Australia, with more than 50 firestorms occurring since 2001, and it’s entirely like we’ll see more of them due to hotter and drier conditions, say the researchers.
However, until now there had been no way to predict their formation.
New model predicts which bushfires become firestorms
Badlan and the team used advanced computer models to incorporate details of the environment (terrain, wind, and atmosphere) and the fire’s shape, size and intensity, to determine how high the plume will be.
Fires that stay in a more concentrated area, rather than spreading out in a fire-front line, are more likely to produce higher smoke plumes and turn into firestorms, the researchers found.
“Previous work attributes these firestorms solely to the total energy released by the fire, however, we have found the shape of a fire is a vital factor in the development of firestorms,” explains Badlan.
The prediction model is being trialled this summer with the NSW Rural Fire Service, and is hoped to help deploy resources more effectively and more safely, as well as getting people out of the danger zone before it’s too late.
“It’s vital that fire managers can determine which fires are likely to transition into a firestorm so that evacuation may occur as early as possible,” adds Badlan.