A warmer Arctic fuels Siberian wildfires

Global warming, says a Chinese study, promotes wildfires which, in turn, reduce the frequency of rainfall leading to a vicious cycle

by Matteo Cavallito

 

The frequency of wildfires in central Siberia has doubled in the last twenty years and the phenomenon is likely to worsen in this century. That means vast areas of forest destroyed and high CO2 emissions as a result of the dispersion of carbon stored in the burnt soil. A decisive influence on the phenomenon is, of course, the climate change in the Arctic region where, scientists explain, temperatures are expected to rise faster than in the rest of the world. This was reported in a study by Nanjing University, in China, published in AGU Advances, the journal of the American Geophysical Union.

Drought and soil desiccation as key drivers

‘By integrating in-situ and satellite observational data sets as well as chemistry-climate coupled modeling,’ the researchers explain, ‘we find that central Siberia has featured the most prominent wildfire escalation during the past two decades, which is closely related to hydrological drought with decreasing rainfall and drying soil under a fast-warming Arctic.’ In the observed areas, says a statement from the American Geophysical Union, water vapor in the atmosphere is condensing around aerosol particles in the air thus creating the droplets. The problem, however, is that these are often too small to form raindrops.

The cloud condensation nuclei, in other words, end up creating a vicious circle that leads to the suppression of precipitation by fires and a consequent increase in the probability of their occurrence.

“As the Arctic warming is projected to continue, wildfires are estimated to more than double by the end of this century,” the research says.

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Increasing likelihood of wildfires

In detail, the authors used data from the Moderate Resolution Imaging Spectroradiometer (MODIS) instruments of the Terra and Aqua satellites. In this way they could track fire activity between 2002 and 2022 and combined it with data on fire smoke, regional climate and permafrost extent. They then used another model, the Community Atmosphere of the Community Earth System Model, to simulate the aerosol-climate interaction over Siberia.

The authors then calculated an indicator, called the Fire Weather Index, which measures the probability of a fire starting and spreading. The index showed a 10% increase in the probability due to the condensation effect, which can reach 40% in areas with high fire intensity.

Flame intensity could increase by 350%.

In addition, simulations of future scenarios suggest that reduced rainfall could cause an estimated 28% to 39% decrease in soil moisture in the region by 2100. ‘On the basis of the correlation of fire intensity with soil moisture, the fire severity over this region is predicted to increase by 200%–350% by the end of the 21st century,’ the study explains. Moreover, this intensification could worsen due to an increase in the frequency of lightning strikes.

‘Even worse, under Arctic warming in the future, the deposition of fire-emitted carbonaceous aerosol may accelerate snow melting and increase fire frequency in what had traditionally been a low flammability landscape, presenting new challenges for fire management and climate adaptation,’ the scientists conclude.