‘Zombie wildfires’ that can smolder underground all winter appear to be increasing in the Arctic

The Swan Lake Fire on Wednesday, June 12, 2019. (Photo by Kale Casey/Alaska Division of Forestry)

A recently published study examines the phenomenon of holdover or “Zombie wildfires” in Alaska and Canada. The fires, which smolder underground through the winter and flare up the following spring, appear to be increasing, due to climate change.

The study published in the journal Nature was led by researchers at a university in Amsterdam, aided by University of Alaska Fairbanks scientists. Randi Jandt is a UAF fire ecologist and co-author of the paper. She says holdover wildfires weren’t historically tracked until the last 20 years, but appear to be increasing.

“Everyone I’ve talked to — all these long-time field people in the fire business up there — kind of think it is increasing in frequency and now we’re starting to expect these things after some of our bigger fire seasons,” she said.

The study points to more than 40 overwintering wildfires reported in Alaska since 2005, and Jandt says climate change is suspected to be a key factor.

She says when Alaska’s peat rich soils dry out, they can provide an environment where fire can smolder through the winter.

“It penetrates down into the lower parts of that duff,” she said. “Or, if it can get under the roots of some trees and be protected from moisture, it can hold that fire.”

Overwintering fires pose challenges for firefighters.

“That smoldering overwinter can leave a bit pit of ash or maybe even a finger of fire that creeps out from an area that looks green on top,” she said. “But it’s kind of underground, so they have to root these things out and it takes a lot of water.”

Jandt says holdover fires typically crop up in the spring, and that requires firefighting agencies to be ready to respond earlier in the season.

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