Recent extreme fire behaviour pushes scientist to develop new forecast system

Extreme bushfire phenomena – like deep flaming and fire storms – are becoming more frequent, but have always been hard to predict.

A new fire safety system, designed to complement the current system, could help to forecast when these extreme events might happen in southeastern Australia, giving authorities and the public more time to respond appropriately.

“The fires are having these new, unexpected and massive impacts,” says Rick McRae, an adjunct professor at the University of New South Wales Canberra, and developer of the system.

McRae first began working on this system two decades ago, following the 2003 Canberra bushfires, which burnt into the suburbs in a matter of hours.

Those fires saw 4 deaths and 435 injuries, along with the loss of 487 homes and 23 government or commercial buildings. Almost 70% of the Australian Capital Territory was burned.

“The 2003 fires, in my view, are the most scientifically important fires ever, because there’s so much to learn from them,” he says.

“Unfortunately, what climate change has done is to allow things to continue to escalate.”

The Canberra fires saw a pyrocumulonimbus cloud – a fire-induced thunderstorm.

“These things are big, they go 15 kilometres up and they hit the top of the troposphere, the bottom of the stratosphere,” says McRae.

There was also a fire tornado caused by the extreme fire weather.

“There’s not just these fires that punch upwards into the next layer of the atmosphere. There’s also a type of fire that stays low. And it’s driven by what’s called the foehn wind,” says McRae.

Foehn winds are dry, warm winds that flow down slopes.

“During the Black Summer, they were the cause of about 50% of the bad fire impacts,” says McRae.

Both of these types of fire can exhibit “deep flaming”, where a fire front can go for hundreds or even thousands of metres rather than the more typical tens of metres.

“This new model is designed to include all these sorts of things that we’ve been learning,” says McRae.

“The Australian Fire Danger Rating System [AFRDS] is based on the standard type of fire, the line fire, and fire services in Australia do a very good job in mitigating the risk.

“But on top of that, we’ve got this new type of fire that’s driven by deep flaming. This new model is designed to augment what’s been put in place for normal fires and start to give people a better clue of when there’s going to be a switch to what we call dynamic fire behaviour.”

The model is hierarchical: its first level is at a regional and seasonal scale, using Canberra temperatures as a proxy for seasonal change. Then, it uses river drying data and finally weather forecasts to develop a risk rating for individual days.

It’s designed to work for “forested country between Brisbane and Melbourne”, according to McRae. It may also be useful in Tasmania, although it hasn’t been explicitly tested there.

McRae has used the model retrospectively to check bushfire conditions over the last 20 years, and found it to be highly accurate.

This year could bring more extremes, according to the model.

“Every time we go into a bad fire season, we expect things we haven’t seen before. So who knows what will come in the summer,” says McRae.

“It’s not just that things are getting warmer. It’s that interactions between things are changing.”

McRae has published a paper about the system in the Australian Journal of Emergency Management.