Q&A: What you need to know about the science of forest fires

Over the last 35 years working as researcher with the Canadian Forest Service within the federal department of Natural Resources Canada, Tim Lynham has become an expert in fire behaviour, prediction and ecology. The latest project Lynham is leading focuses on developing remote sensing technology, and will build on Canada’s strength at fire forecasting. Against the backdrop of all that’s happening in Fort McMurray, Lynham spoke from his post in Sault Ste. Marie, Ont., about how fast and furious forest fires burn, how plants and animals survive, and the stunning power of fire over wind and water.

Q: Are fires different depending on where they’re happening?

A: They’re different depending on what type of fuel type they’re happening in. So in the Fort McMurray case they’re just on the edge of the forest greening up from the spring time. So they’re dealing with the dead vegetation from the year before as well as live vegetation, which is not really moving much water. There are no leaves, and the sun is penetrating right to the ground. Now, that varies across the country mostly depending on your latitudes. So we’re probably behind them in the Soo because we’ve had a cool spring, and they’ve had a warm and dry one. The big difference is mostly to do with the fuel type, until you get to British Columbia and you have a whole new thing, which is [sloped] terrain. So fires go up hills very quickly and they come down very slowly. Going up the hill it’s like having a stronger wind pushing the fire. It’s the same thing anytime you have a wind pushing a fire on a flat surface, a stronger wind will move the fire faster.

Q: How would the terrain in Alberta impact the way the fire moves?

A: It’s relatively level in Fort McMurray. If you go to Western Alberta it’s very mountainous because now you’re getting into the foothills. But what’s going on in Fort McMurray and northwestern Canada right now is that they have available fuel that is not green yet—it’s early in the spring so it’s not greened up. We’re getting no effect from green vegetation but incredibly high winds, incredibly high temperatures and remarkably low humidities. About 10 per cent humidity is what they’re getting and most fires don’t become much of a problem if the humidity is above 30 per cent. But when you get down to 10 per cent it means anything that’s dead and dry is ready to burn.

Q: What’s normal humidity where there would be no threat of a fire?

A: Most days your humidity is going to be between 40 and 60 per cent. If it hits 100 per cent you have rain. When you get these super dry air masses that they have in Alberta right now then you’re dropping well below 30 [per cent], and in their case they’re down to about 10 per cent, and that is quite remarkable. That’s a bad situation.

Q: I’ve read about the fires jumping over bodies of water. How could that happen?

A: There’s a lot of material that are attached to the forest trees. Some of it is bark; birch bark trees, for example, have very curly bark on them, and that can be carried up in the draft [or] the heat and then burned in the column of the fire. The wind carries it out in front and drops it down while it’s still burning. It can also be parts of a tree that get carried up because these things have tremendous winds. When these fires get going, the wind’s interior can easily be 150 miles an hour. It’s not widespread, but they can rip out trees, they can carry a lot of big material, it’s lofted into the column of the fire, it’s burned very thoroughly and then it’s thrown out and it drops down and it could start another fire.

Q: So how does fire make it to the other side of a body of water?

A: It’s burning up to the water, but there’s such a tremendous column [of fire that] it’s carrying a lot of burning debris. The column usually leans out over the water. You can imagine the wind is pushing from behind, the surface is burning, but the column is tilted forward, and that column is carrying burning debris that gets deposited on the othe side of the river, which starts spot fires and the fire keeps running. So it doesn’t surprise me that it jumped the river in Fort McMurray or the highway because I’ve been on wildfires where it jumped over a kilometre out into lakes and took out islands that were a kilometre from the shore. So you have to have a very large body of water to stop the embers from jumping.

Q: What do you mean by the fire’s column?

A: As the fire is burning it’s creating a tremendous amount of heat. Because it’s hot air, there is water vapour and carbon dioxide being released when the fire burns. Hot air is being carried upwards very rapidly—that is the column. So material leaves the surface of the forest still burning and is carried up into the column, and it either falls back down or it burns up in the column or it’s deposited out in front of the column. And that’s what we call spot fires.

Q: It almost sounds like a tornado. Is there is any likeness?

A: Actually, they are tornadoes. There was one recently in, I think, Manitoba this spring where it was a grassfire and some of the firefighters escaped to the water because it turned into a tornado. We’ve experienced these small tornadoes on our own fires in Ontario. Several years ago there were two gentlemen who were travelling in a pick-up truck through a fire in Manitoba, and it created an enormous tornado and it sucked their truck into the fire and rolled it across the terrain and they were killed. So these are small and ferocious tornadoes that don’t last long. It’s not like a normal tornado that we hear about in North America. They are limited and very powerful. They can rip trees out of the ground. They can flip vehicles.

Related: How big is the Fort McMurray fire? We map out the data

Q: Is it basically a tornado [spawned by] a fire?

A: What happens is the fire is generating a lot of energy and that energy has to go somewhere. The wind wraps it into a vortex, and that is the tornado. So the energy on the fire is actually creating the tornado, and as soon as you remove that energy then the tornado will cease to exist. The most intense part [of a fire] is at the front and that can move depending on the wind.If the front of the fire is very long, and the intensity is very high then there’s a strong chance of a tornado. But these tornadoes don’t take off and run across the north like a tornado does in the United States. They’re very local to the fire and once they lose energy they dissipate. But they can do a lot of damage around the area of the fire.

The real problem with tornadoes is [if] they start to throw big material in all directions. They’re a big danger to firefighters and anyone who is around them. They can drop big chunks of burning material on you.

Q: So would this tornado phenomenon be part of what’s happening in Fort McMurray?

A: I can’t tell you because I haven’t heard any reports of it. What has happened in Fort McMurray is thunderstorms from the fire. When you burn woody material you produce water vapour. That water vapour is rising very rapidly in a hot column and as it rises it cools just like happens in a normal thunderstorm, and it produces water droplets that form around the soot material, which has been burned in the fire. So if you look at the condensation nuclei of each water droplet, it’s usually a little black sooty particle. And then there is rain and thunder but the column is so hot and dry that the rain never hits the ground and we get what is called dry lightning. That has been documented in Fort McMurray. So the main fire is creating thunder storms in the afternoon, and those thunder storms are creating dry lightning and those lightning strikes are creating new fires.

Q: So how fast can fires move?

A: There are some extreme examples in Canada but usually about the fastest would be about six, seven or eight kilometres per hour. That doesn’t sound so fast, but imagine trying to run through a forest at six or seven or eight kilometres an hour—jumping over logs—it’s not easy. So it’s quite a high speed. I think there’s documentation probably around 10 [kilometres an hour] on some fires.

Q: How hot do fires get?

A: Fires are about 700 to 1,000 degrees Celcius. It doesn’t matter where they are. If you’re burning woody material it’s going to be [in that range]. But what’s different is the intensity. The intensity is the rate of energy released, and that can very from 200 kilowatts per metre to 100,000. And that’s what kills people. That’s what was threatening people on the highway in Fort McMurray. So the temperature is relatively stable and predictable. The intensity depends on how much fuel and how fast the wind is blowing.

Q: How can the intensity kill people?

A: Imagine if you’re standing near a bondfire in your backyard, if you get a little bit too hot you can jump away, and that will reduce your problem. But if you tried to move closer it would get worse. You can take that heat for a little while, but if the fire becomes more intense, your body can’t cool you rapidly so you need to get away from it.

Q: How does a forest fire change once it gets to the urban edge in terms of heat or speed?

A: Usually it slows down because there’s less fuel. But in the case of Fort McMurray not only did the houses become fuel but there may have been dead grass from the previous year. Any shrubs in your yard that are coniferous—cedars, junipers, those would burn very readily. Often the houses burn because embers land on the roof, and if it is combustible, which many of our North American roofs are [because] we have tar shingles, then the fire works its way through the roof. Once it gets into the house, that’s it. So it’s not like the fire roared up to the house. Often the fire doesn’t move right up to the walls of the house. It’s often embers fall on the roof, the roof becomes engulfed in flames, and once the roof breaks down then the whole house can burn.

Q: Are there other incredible things that fires can do?

A: We actually have video of fires that created these little mini tornadoes and they’re so strong that they actually exit the forest at the edge of a lake and they’ll move across the lake and they create what we call a water spout. These might be about 10 metres in diameter and it’s just like it’s swirling like a tornado but it causes a standing wave which is four, five or six feet. And that can move across the lake because there’s so much energy and then eventually it’ll hit the other side of the lake where there’s unburned forest and it will just dissipate because it loses all of its energy. It’s quite remarkable to see. It looks like a water tornado, but we call it a water spout because it’s not as fierce as a tornado. But you wouldn’t want to be in a boat and run into this thing because it would knock you over. It’s very powerful. It’s kind of a rare event.

The other thing we’ve seen [is] 50 or 60 foot spruce trees that are engulfed by the fire, but before the fire reaches them there’s so much suction that it actually rips the trees out of the ground and they shoot off into the column like a rocket. And then they burn up in the fire column, and they can be deposited afterwards like spears into the ground. So you can go back into the fire afterwards and you can find maybe like an 18-foot piece of tree, like a trunk of a tree, but it’s upside-down and the tip is buried six feet in the ground so it comes down like a spear. It’s like a javelin. And we know that the wood has been in the fire because if we pull it out of the ground, the buried part is covered in charcoal but the part that’s sticking above the ground looks like a piece of driftwood because it’s been sandblasted by the tornado. It looks just like a piece of driftwood, but everything below the ground level is charcoaled, which means it was in the fire column and it got deposited into the ground like a spear.

Q: What happens to all the animals in the forest?

A: Birds try to fly away, but the ground nesters often tend to succumb to the fire. Small animals like rabbits will usually move into an underground hole and there’s enough of a canal underground that they’re protected from the heat because heat only penetrates about one or two inches below the surface of the ground. The large animals really have no choice. They run. But in a large forest fire typically about five per cent of the large animals will be killed, and that’s because they get trapped. That five per cent mortality is about roughly equivalent to the mortality you see with those same large animals during a very severe winter, like deep snow and lots of cold.

Related: Is there any hope for the pets of Fort McMurray?

Q: I remember learning that forest fires are good for the environment. In what way?

A: We do not tolerate fire in our communities in Canada. But if you look at a fire that’s burning out in the forest away from people, then it does have positive ecological benefits. The big thing is it releases a lot of nutrients very quickly, and those are taken up by the regrowth of the forest. You’ll see new plants sprouting within six weeks if you have rainfall. Once a fire stops and if there’s moisture the new forest will start growing almost immediately.

Q: So if we went to this charred land in Alberta in six weeks we might actually see new growth?

A: If the fire was 100 per cent out, say in the Fort McMurray area, and if you got a lot of rainfall to get things going you could start to see grasses coming up again, you’d see poplar, birch trees starting to sprout from the base. You wouldn’t see the pine trees until the next year because they would start from seed, and that would be too small. But it’s only going to happen when the fire is out and youhave moisture to initiate the regrowth. So you could see that probably within two months. It would be very small but because of the black background you’d be able to see the green growth starting to come up.

Q: What can you say about the work you’re doing in fire forecasting?

A: Canada has been an expert at building forecasting programs for fire behaviour. We have a fire behaviour prediction system [that] is used all across the country that was developed through research efforts with the federal government and the provincial and territorial agencies. We are also looking at ways of monitoring fires in real time using remote sensing. The remote sensing platforms carry thermal detectors, which are very sensitive to heat. They’re either on aircraft or in drones or on satellites. But it’s picking up information using a thermal detector [that] is only about as big as the last joint on your baby finger. It’s digital and can pick up photons [light particles] coming off of fires and tell you a lot of important information about the fire.

Q: The use of drones is intriguing. Is that something we’re doing more and more?

A: The Americans are doing a lot of work with drones. There are several people in Canada who are working on low-level drones to do monitoring for all kinds of forestry and other purposes. We’re interested in using drones at a high level for monitoring fires but we don’t have anything available to us. We’re also working with the Canadian Space Agency and other space agencies to look at the development of satellites that could do fire monitoring from space. These thermal detectors that go on a satellite could be 700 kilometres in space or even higher but they can pick up a fire in your backyard that’s three metres by three metres.

Q: Is there anything important or interesting to know about the science of fire?

A: What’s going on in Fort McMurray is absolutely horrible because we do not want fire in our communities. Just like you don’t want a bonfire going into your house, you don’t want this. But there’s also this beneficial ecological role of fire. Most of our forest depends on fire for its survival. We have to figure out a way to live with fire, but it seems like the amount of fire is going up. We’re warmer and dryer, and that will mean that we will have more fire.

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