The science of a bushfire

Since September 2019, Australia has been battling ferocious bushfires. Katie Haylor spoke with Guillermo Rein from Imperial College London about the crisis there...

Katie - Australia is in the grip of some of the worst bushfires the country has ever seen. Some have died, thousands have lost their homes, millions of acres of Bush had been burned and up to a billion animals may have perished. To find out how these fires work and what's driving them. I spoke with fire specialist Guillermo Rein from Imperial College London.

Guillermo - The situation right now in Australia is overly warm and there are winds, and these are the worst case scenario. It would be literally the fastest fire spread that has been observed in Australia.

Katie - Does the evidence suggest climate change is a factor here?

Guillermo - Unfortunately, we don't know enough to be certain about the role of climate change in the specific fires that are happening in Australia. It cannot be ruled out, if it does have an effect, it is through bringing unprecedented warm conditions to the forest, and making the forest pretty dry and windy.

Katie - I understand that these fires, when they get so very big, they end up making their own weather system.

Guillermo - Fires are self sustaining by the nature of the fuel burning, producing heat that heats up the next fuel layer, and then the fire continues, but there is a point where a forest fire can grow so large that it starts to alter the atmosphere around the fire. Smoke is hot and rises up, so when you have an incredible amount of smoke, it creates these very strong columns of currents that are going upwards that actually drag surrounding air upwards. Smoke has a complex composition. It has soot, it has hydrocarbons, but it also has abundant water.

So then this smoke, under some conditions creates its own clouds and then these actually move around. Also you need incredible amount of oxygen to feed these mega fires and the wind, goes towards the fire to provide the oxygen and the combination of the plume of smoke going upwards, and the sucking in of air creates its own wind, and these winds actually further accelerate the fire. These big clouds formed by the fire could actually produce lightning. Also, the smoke can be electrically charged so farther contributing to the electric charge of of the cloud. These could actually become additional ignition sources, although a fire itself, especially a mega fire, it has plenty of ignition opportunities. Unfortunately the flames itself, but also the embers that they produce and can travel hundreds of metres even kilometres by the wind and then it starts fires hundreds of meters away from the flaming front.

Katie - Given the scale of these mega fires, how on earth do you go about trying to tackle or manage this situation?

Guillermo - Mega fires cannot be suppressed. Firefighters have to take an offensive approach and just wait. While it is a mega fire, the best thing that they can do is move people away from the fire path. The difficulty is in making a good prediction of what could be the fire path. You could make an analogy with trying to predict the path of a hurricane.

Katie - What science is involved in actually calculating or predicting where the fire's going to go?

Guillermo - There is some models now that give it a try, but these tools, they are in their infancy, compared to the true desire of authorities to know accurately what the path of the fire is going to be. These tools just give a sense of direction and it's very important because you don't want to evacuate areas that don't need to be evacuated. We're talking about thousands of fire refugees and you definitely want to evacuate the ones where the fire is going to go, but the science is advancing as we speak.

Katie - How would you expect these mega fires in Australia to behave in the near future? Is it possible to predict?

Guillermo - We wish we could. It's not possible. Maybe if you ask me this question in 10 years time, I can give you better news. What we're seeing is more big fires. The term mega fire being in vogue way more often. So every single year we have fires in Australia, in Subsaharan Africa, Amazons, Mediterranean, California. But some years as is happening more recently, the fires are much larger and much more damaging, to people, property and environment. That is the trend, it is what is concerning fire scientists. We don't want to be waiting too long to start doing things differently. Australia in particular seems to be now in the need of doing something different.