Though winter is coming, fire crews are on the lookout for zombie fires that can spring back to life

Though wildfire season in Alberta is officially over, the battle is far from done.Fire crews continue to keep watch forfire that is burning undergroundand could flare up again in the spring.

Fire can continue to burn unseen in organic matter called peat, which has been drying out due to drought, thereby making it more receptive to burning.

Even as temperatures drop, that doesn't mean peat fires will completely peter out.

"Since it is organic material, it continues to burn underground and basically smoulders away throughout the winter," said Tanya Sawicki, a wildfire technologist with Alberta Wildfire.

Sawicki explains the fire can spread like tentacles underground.

"They can grow quite a bit actually. It could be probably kilometres really if we let it go," she said.

The fires do not need much oxygen to burn and there won't always be flames or smoke, which make the fires difficult to track.

Alberta Wildfire doesn't know where these fires sometimes known as holdover or zombie fires are burning in the province, but says the record fire season makes them likely.

The wildfire service is monitoring some areas for smoke, and relieson reports from the public and industry to be able to address peat fires quickly.

"If we don't deal with them now, we're not sure what we could see in the spring. Basically, if we don't have as much precipitation as we usually get, we'd be more concerned with them popping up in the spring," Sawicki said.

Hard to find, hard to put out

Ellen Whitman, a forest fire research scientist with Natural Resources Canada, said these types of persistent fires, which can burn in peat but also anywhere there is dense and compact fuel on the surface that is organic, can be difficult to put out.

"A lot of that has to do with the fact that they're actually very difficult to detect," she said.

"They don't necessarily have a whole lot of smoke and they certainly don't have visible flame. It can be under layers of soil or also under layers of snow.It can be really challenging because we can't necessarily detect them with thermal imaging."

To put the fires out, the peat needs to be exposed to air and then flooded with water, which requires a lot of time and manpower.

Whitman said there are examples of these fires flaring up again in the spring because they were never fully extinguished.

"They're really extreme examples of fires burning over multiple, multiple years," she said.

And, like Sawicki, she is looking ahead to implications for the next wildfire season, pointing to factors like drought conditions and the possibility of another warm and dry spring.

"That situation, again, really suggests that we may have quite conducive fire weather next year in 2024 right off the bat, which would be, again, a concern for these holdover fires.

In severe fire years, Whitman said, holdover fires can make a substantial difference to how much land burns.

According to one study published in Nature in 2021, overwintering fires in boreal forests in Alaska and the Northwest Territories were responsible for 0.8 per cent of the total burned area between 2002 and 2018. However, in an extreme year, those fires were responsible for38 per cent of the area burned.

Finding a single ember

Moe Aboughoushe works on the winter crew with Alberta Wildfire, which focuses on fire suppression, reclamation and fire prevention, and is responsible for responding to peat fires in the winter.

"If we do see a peat fire, it's all hands on deck and getting as much water as we can on that fire just to prevent it from holding over for the winter and popping up again in the spring," he said.

Firefighters are also being proactive and using a technique called cold trailing.

"Cold trailing would be a tool that we have in order to find any remaining heat within the fire. And it's as simple as using your hands," Aboughoushe said, as he demonstrated running his hands through soil on peatlands.

"What I would do is go in with my hands and look around for heat, not warmth, but actual heat. We can't leave a single centimetreuntouched because there's always that chance that there will be a single ember in there. A single ember can always restart and cause another forest fire to roll through where it's already rolled through."