Tech

‘Zombie’ fires in Alaska and Canada may be becoming more common

Forest fires in the Arctic can smoulder all winter long

Al Henkel/NBC NewsWire

In the northern hemisphere, “zombie” forest fires that burn in the summer then smoulder over winter and reignite in spring may be becoming more common. A model suggests they are associated with warmer summers, which are happening more often as the climate warms.

Rebecca Scholten at Vrije Universiteit Amsterdam in the Netherlands and her colleagues created an algorithm based on satellite imagery to track the occurrence and characteristics of the zombie forest fires in Alaska and the Northwest Territories of Canada between 2002 and 2018.

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The fires made up about 0.8 per cent of the total burned area over the period, but this varied annually, with a single zombie fire in Alaska responsible for 38 per cent of the burned area in 2008.

“It seems to be that they have become quite common now, as in we have one or two every year, with large occurrences happening after large fire years,” says Scholten. “What is interesting about that of course is that we are seeing more large fire years and hotter summers with climate warming.”

Overwintering fires have been anecdotally reported for years.

“It’s never been very clear whether this was that thing they saw that one time or whether it’s something important that happens often enough that you need to take note of it,” says Steven Cumming at Laval University in Quebec, Canada. “It looks like the answer to that question is, maybe it does. There’s not tonnes of them yet, but there could be a lot more in future.”

Overwintering fires are more common in lowland areas with thick organic soils and dense tree cover. The fires burn with high intensity deep into the soil, which could be what enables them to survive winter.

Scholten hopes that knowing the features of these events will help us develop better fire management strategies.

“It would be very interesting to see how important this phenomenon is across the rest of the high latitude regions,” says Thomas Smith at the London School of Economics. “Siberia, for example, where we know there’s a lot of this overwintering fire. It would be very interesting to see this algorithm expanded to cover the rest of the Arctic.”

Journal reference: Nature, DOI: 10.1038/s41586-021-03437-y

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