As wildfires rage across parts of Canada, one fire in particular is highlighting concerns about so-called “zombie fires.”
Authorities in the Northwest Territories are monitoring a large fire that has flared up after lying dormant underground over the winter months.
Fires that continue through the winter in Canada were once considered a rare occurrence, but experts warn that these events are becoming more common as temperatures get warmer and less snow falls.
According to the British Columbia Wildfire Service, a “zombie fire” — more commonly known as a hibernation fire or a left-over fire — occurs when a forest fire that burned deep underground the previous year continues to smolder throughout the winter.
The agency warns that these “residual hotspots” could re-emerge as warmer, drier weather arrives in the spring.
Jennifer Baltzer, associate professor of biology at Wilfrid Laurier University and the Canada Chair in Forestry and Global Change Research, told CTVNews.ca in a phone interview Monday that “zombie fires” smolder in biomass, such as tree roots and trunks or in peat soils , of the affected landscape.
Such phenomena could cause the wildfire season to start earlier than expected and last longer, she said. Balzer added that winter fires also have the potential to cause much greater changes and losses of ecosystem carbon than a simple wildfire.
“A single-season fire burns all season and then dies out, while a smoldering fire continues to burn wood and peatlands throughout the winter — very, very slowly — but we continue to see burning throughout the winter,” Balzer said.
According to a 2021 study, winter fires generally accounted for a small amount (about one percent) of the total area burned in the Northwest Territories and Alaska between 2022 and 2018.
However, researchers from the University of Amsterdam and the University of Alaska Fairbanks found that there was a “surprising” increase in the number of winter fires reported in individual years.
In Alaska, for example, overwintered fires accounted for 38 percent of the burned landscape during the 2008 wildfire season, according to the study.
Experts suggest that “zombie fires” may become more common due to climate change, as the hot, dry conditions associated with years of severe fires may lead to this deep burning of carbon-rich biomass.
A study published in 2019 found that rising summer temperatures associated with climate warming could promote the survival of overwintering fires in the future, threatening boreal regions, including the subarctic, arctic, Northwest Territories and northern areas in Ontario, Alberta and Saskatchewan.
Balzer, who leads a team of researchers in collecting field data on “zombie fires” in the Northwest Territories, hopes to further analyze how these fires affect carbon loss and forest regeneration in Canada.
Balzer explained that shrubs that recover quickly from wildfires can do so because of underground plant systems. However, “zombie fires” damage these systems, as well as tree seeds, which “impede reproduction and recolonization of these sites” after a fire, she said.
“This is a cause for concern because of the changing fire activity in the boreal forest,” Balzer said. “High-latitude systems are warming at about three to four times the rate of the planet… And this really fast warming makes these systems more flammable… [resulting in] larger burnt areas, more severe fires and more frequent fires.”
Balzer said winter wildfires are “inextricably linked to climate change” as they become more common after years of increased wildfire activity that has steadily increased amid global warming.
With that in mind, Balzer said preventing “zombie fires” will require reducing fossil fuel emissions to slow the overall production of greenhouse gases that lead to global warming.
While Baltzer acknowledges this requires a global effort and is beyond the scope of her research team, she says they are working to provide information to fire managers to support a better understanding of where the “zombie fires” are in Canada , to help inform understanding of the behavior of these fires and how to respond.
View the map showing fires burning in North America, provided by ESRI Canada, in full screen
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With files from The Canadian Press
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