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Every winter Alaska and northern Canada are covered in snow, wildfires are extinguished in summer, and are calm, at least on the surface. Under all the white silence, some of these fires actually continued to smolder underground, chewing on carbon-rich peat, paying precious time for it. When spring arrives and the cold landscape defrosts, these “overwintering” fires emerge from below, which is why scientists call them zombie fires.
Now a new analysis In the diary natural It is the first time to quantify its scope and show the conditions most likely to bring the fire back to life. Using satellite data and reports on the ground, researchers have developed an algorithm that can detect fires that have burned for decades in Alaska and Northwestern Canada, dozens of times in total, have snowed, and then ignited again in the spring. Basically, they linked the burn scar to the nearby area, and then a new flame ignited nearby. (They ruled out situations that might occur simultaneously with thunderstorms, and situations caused by accidental fires close enough to people). They calculated that between 2002 and 2018, the winter fires on these lands accounted for 0.8% of the total burned area. Although it sounds small, it has attracted attention for a year: In 2008, a zombie fire actually caused 38% of the total area burned to burn.
Such an outbreak may mark what is about to happen in the rapid warming of the Arctic. Although 2008 was a very bad year, it is no accident. Rather, it is part of the pattern of conditions where zombie fires are most likely to occur. The lead author of the new paper, Rebecca Scholten, an earth system scientist at the research university VU Amsterdam, said: “They appear more frequently after hot summers and fires.” “Indeed, in the past 40 years, we can prove this. Increased.” For example, the particularly active fire years in 2009 and 2015 in Alaska, and the particularly active fire years in 2014 in the Northwest Territories, produced multiple overwintering fires in the spring of the following year.
The northern soil is full of peat and dead vegetation Essentially enriched carbon. When wildfire burns in the Arctic landscape, it also burns vertically in this soil. Soon after the ground fire ran out of plant fuel, the peat fire continued to smolder under the dirt, moving deeper and sideways. In their analysis, Scholten and her colleagues found that this situation is most likely to occur after the hot summer, because it will make the vegetation drier, which can lead to more catastrophic consequences. Sander Veraverbeke, an earth system scientist at the University of Amsterdam, co-author of the new paper, said: “The more it burns, the deeper it can burn in the soil.” “The deeper it burns, the fire The higher the chance of hibernation.” Even if the rain falls in autumn or the surface freezes in winter, water cannot penetrate into the soil to completely extinguish it.
Then spring arrived and the ice subsided. These hot spots will open up, looking for more plants to burn on the edges of the original burn scar. Scholten said: “Basically, after the snow melts, we already have dry fuel.”
They believe this happened in 2008 and other frequent zombie fires. The fire went deep underground, which made them better through the winter. Researchers believe that these conditions are becoming more and more common. “We do show that since 1975, the fire years associated with the hot summer have become more frequent, and we hope that this trend will continue,” Veraverbeke said. “This will also lead to more frequent overwintering fires.”
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