Why are the ‘Zombie’ fires in Siberia a ticking climate bomb?

1 July 2021

Written by: Anthony Sevrin, Senir Data Scientist, AXA Climate, anthony.sevrin@axaclimate.com

'Zombie' fires in Siberia

Siberia represents more than a district, it’s a land of dream and adventure. We have seen vast frozen plains covered with snow and taiga and traveled by wild horses as described by Jules Verne in Michael Strogoff. But over the past few years, unusual events have been occurring in this postcard landscape: Gigantic Wildfires.

Figure 1: Spatial extension of Siberia: Siberian Federal Districts (dark red) and historical Siberia (red and orange) (1)

What happened in Siberia in the recent past?

Since 2019, Siberia faced a dramatic increase in wildfire number and extent. In July 2019, almost 2.6 million hectares of forest burned simultaneously over Siberia. It was nearly the size of Belgium (2). In addition, we estimate that a total of roughly 5.3 million hectares of land was burnt that year (3).

Figure 2: (a) Wildfire locations (radiative Power) in June-August 2019 (4); (b) Summer 2020 Wildfires Total Radiative Power (5) (6)

In the summer of 2020, Siberia again suffered from large wildfires (3.4 million hectares according to MODIS data) especially in extreme northern latitudes (above 65°N). Areas near the arctic circle are usually less exposed to wildfires because of their low surface temperatures, but over the past few years the relative number and the extent (burned area) of wildfires have increased dramatically.

Is this evolution linked to Climate Change?

2019 and 2020 wildfire seasons in Siberia were mainly due to very high temperatures (Figure 4). Temperatures have a direct link with the number and intensity of wildfires because the longer a heat wave lasts, the drier the vegetation becomes, which is very favorable to the ignition and the spreading of fires (Figure 5).

Figure 4: Land surface temperature anomaly compared to 2003-2018 baseline in summer 2020 (7)

It is well known that we can expect a rise in the temperature in the near future due to Climate Change. But the effect of this rise on wildfire activity has already been noticeable in the last years (8). This effect is particularly striking for peatland- stored carbon situated North of the Arctic Circle. With temperature rising, historically frozen soils are expected to thaw as the planet warms, making them even more vulnerable to wildfires. [ref 9]

Why are Siberian wildfires so special?

Wildfires in Siberia are peculiar for two reasons: “Zombie” fire and carbon release in the atmosphere.

“Zombie” fires, also called as wintering fires, are wildfires that can spontaneously re-ignite months after being extinguished.

How is it possible? It’s mainly due to the composition of Siberia’s soil which is made of peat layers. Peat is an accumulation of partially decayed organic matter and therefore can burn under low moisture conditions. That’s why after its extinction on the surface, the fire can continue underground for months and re-ignite at the surface the following year a few kilometers away. It is likely that most of the 2020 wildfires were ignited by peat fires “which have been smoldering underground during the winter months (10).

Figure 5: Peat fire can continue 1 year underground and restart a new wildfire (11)

The second specificity is the massive amount of carbon released into the atmosphere. Between June and August 2020 in Sakha Republic, Copernicus estimated that wildfires released 540 megatons of CO2 (12), which corresponds to roughly Canada’s CO2 emissions during an entire year! If we consider that each year the world roughly emits the equivalent of 51 gigatons of carbon into the atmosphere, we can conclude that 2020 Siberian fires correspond to more than 1% of this excess. This large amount of emission is due to the number of trees burnt but also due to peat fires themselves. Indeed, peatlands are the most carbon-dense ecosystem, and this carbon is released into the atmosphere when it burns. In addition peat, unlike trees, cannot regrow and therefore won’t be able to capture part of the emitted carbon.

Peat fires and carbon emissions are the most favorable ingredients to build a positive feedback loop for wildfires. Carbon emissions lead to warming that favor wildfires which can restart over and over again emitting more CO2. That’s why the situation in Siberia should be carefully monitored.

How can we adapt or avoid this situation?

In order to avoid this situation, we can act on three approaches: Prevention, Early detection and Remote Sensing.

Prevention is not specific to Siberia. Some general rules to remember: Forests, especially in the context of drought, become vulnerable. Human activities like industries or tourism need to be strictly controlled. Renovation of infrastructures and prevention campaigns, etc should be held to limit peat fire. Land owners can develop re-wetting strategies and stop draining peatlands (13). Infact, the most dramatic situation is when drained peatlands are abandoned and are stopped being monitored by their owners or the government. It is therefore important to have a collective program to re-wet these fields like in Belarus.

When a wildfire occurs, the use of satellite imageries can allow land owners and firefighters to early detect ignition points and act quickly. We can combine radar satellites data to spot temperature variations with optical satellites to confirm the presence of a wildfire and precisely measure the burnt area.

Figure 6: Sentinel3 image of active wildfires captured on 23rd June 2020 (14)

Finally, we can also use remote sensing, especially radar technologies, during winter to spot the peat fires smoldering underground. Thermic anomalies can be a hint that something is happening in the peat layer. With this technology, we can anticipate the fire re-ignition in the following summer and act quickly in order to avoid its propagation.


Over the past years, mainly because of Climate Change, Siberia has looked more and more like a Song of Ice and Fire. This situation brings a vicious circle: Peat fires unleash huge quantities of carbon in the atmosphere contributing significantly to climate change that in turn contributes to creating favorable conditions for wildfires. To break this loop, we need to invest on prevention by managing peat fields and we need to use remote sensing to detect peat fires and wildfires to kill them in the egg and avoid the spreading.

For more information, contact Anthony Sevrin, Senir Data Scientist, AXA Climate, anthony.sevrin@axaclimate.com

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