“Zombie fires” – which continue to smoulder beneath the frozen surface through the winter and then flare up in the spring – may account for up to a third of the total burn area in the forests in the Arctic Circle, scientists believe.
Also known as overwintering fires, these wildfires have been a relatively rare phenomenon in the cold and wet winters of boreal forests across the vast expanses of Canada, Alaska, and Russia.
But experts believe the numbers of so-called zombie fires are now on the rise – due to a warming climate that allows them to burn deeper into the organic soil and help them sustain over the winter.
In a new study published in the journal Nature, the researchers say their work could help in the early detection and suppression of these fires.
Sander Veraverbeke, an associate professor at Vrije Universiteit Amsterdam in the Netherlands and one of the authors on the study, said: “On a positive note, our findings can help firefighters.
“You could monitor the location of last year’s fires from planes or satellites and extinguish them when they are still small.
“We will continue to research this scary but fascinating phenomenon in Northern America and also in Siberia, in cooperation with local firefighters, because it seems that overwintering fires are here to stay.”
Last year, wildfires in the Arctic Circle broke the previous year’s carbon emissions record, emitting a record 244 megatonnes of carbon dioxide.
Vast areas of boreal forests across Siberia, Alaska, Greenland, and Canada went up in smoke, thought to be fuelled by remnants of the previous year’s blazes.
Lead author Rebecca C Scholten, a PhD student at the Vrije Universiteit Amsterdam, said: “Boreal forest soils have a thick layer of organic material consisting of peat and decomposing spruce needles.
“These contain much more carbon than the trees above.
“With low oxygen levels under the snowpack, overwintering fires smoulder slowly, only to flare up again when the snow melts and dry conditions arrive in the spring.”
As part of the study, the researchers analysed satellite data from the Arctic Circle gathered between 2002 and 2018.
They identified that zombie fires were responsible for nearly 1% of the total burned area over the study period, but said this varied in individual years and, in one year, was as high as 38%.
The researchers have developed an algorithm to identify zombie fires in some of the affected regions.
Ms Scholten said: “Previously overwintering fires were reported as a rare freak phenomenon.
“There are more overwintering fires after hot hummers with many large and severe fires.
“In 2010 for example, they caused 22% of the burned area in Alaska.
“Since 1975, summer temperatures in Alaska have been rising and so has burned area.
“Because of this, we expect that more overwintering fires will occur with climate warming.”