May 16, 2024 - Energy & Environment

"Zombie fires" re-emerge in Canada, a legacy of the 2023 fire season

Flames from a wildfire in Canada are seen against a dark sky

Smoke rises from a wildfire in western Canada on Tuesday. Photo: Cheyenne Berreault/Anadolu via Getty Images

Smoldering combustion beneath northwest Canada's boreal forests has emerged onto the dry surface, re-igniting into fast-moving flames amid unusually warm, dry and windy conditions.

Why it matters: The fires that have emerged this month are a threat to homes and businesses and show how a wildfire season worsened by climate change can defy a clear end date.

  • Thousands of people have fled their homes as a variety of blazes, including some that started for the first time this year, advance toward communities.
  • Threatened areas include Fort Nelson and Fort McMurray.
  • The latter city in the country's oil sands region was the site of a devastating wildfire in 2016.

The intrigue: Climate scientists and wildfire specialists had suspected some overwintering ("zombie") fires might reappear, following the country's worst wildfire season on record last year.

  • More than twice the acreage of the previous record-holder burned in 2023, fire expert Mike Flannigan told Axios.
  • Last year's fires only ebbed when the snows arrived; in the boreal, some of them crawled under the snowpack and waited out the cold season.
  • Now they have emerged, detected by satellite heat sensors hugging the edges of burn scars from last year.

What they're saying: "We are certainly seeing a lag effect of last year's severe fire season, continuing to play out in real time this spring," Merritt Turetsky, a climate researcher at the University of Colorado at Boulder, told Axios in an email.

  • "While persistent drought conditions certainly are at play, many dozens of overwintering fires that continued to smoulder through the winter are providing additional ignition sources," she said via email.

Between the lines: Turetsky said overwintering fires are not a new phenomena, since they are similar to coal fires that can burn for years in some cases.

  • But they are especially prominent this year.
  • They are also difficult to study due to the remoteness of the region, but field campaigns are the best way to gain insights into how they work.
  • Research she conducted with colleagues in 2022 showed that zombie fire locations tend to be located in drier forests that have large amounts of biomass and debris. However, they can also burn in thick, relatively moist peat layers that can sustain slow, smoldering combustion, she said.

Threat level: Zombie fires can diminish ecosystems' ability to store carbon and regenerate forest cover and peatlands, making one of the world's best natural carbon storage areas less effective, and hence hastening global warming.

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