Increases in Land Surface Temperature in Response to Fire in Siberian Boreal Forests and Their Attribution to Biophysical Processes

Wildfire is the most prevalent natural disturbance in boreal forests and impacts climate through biogeochemical (e.g., greenhouse gas emission from biomass burning) and biophysical (e.g., albedo [ET], evapotranspiration [ET], and roughness) processes. We used satellite observations to investigate the immediate (i.e., 1 year after fire) biophysical effects of fire in Siberian boreal forests. We found that boreal forest fires have a net annual warming effect (0.0728 to 0.325K) due to strong summer warming and weak winter cooling. Fires also increased the diurnal temperature range and seasonal amplitude. These effects are strongest in summer and significantly higher in evergreen than in deciduous coniferous forests. Decreases in ET contributed to warming effects in summer, and increases in contributed to cooling in winter. Our results suggest that the increase in observed land surface temperature immediately following fires in boreal ecosystems is most likely due to reduced ET leading to a strong positive feedback on the surface radiative budget. Plain Language Summary When wildfire burns forests, it affects local climate by changing the surface energy budget and distribution because of changes in albedo (alpha) and evapotranspiration (ET). Albedo (alpha) determines the solar energy absorbed by the land surface, with darker surfaces (e.g., forest) absorbing more energy than lighter surfaces (e.g., snow). ET is the energy used to release water from plant leaves and therefore cools the land surface. We used satellite observations to investigate how land surface temperature (LST) changes 1 year after wildfire and how this response relates to and ET in Siberian boreal forests. We found that burned forested areas have a higher annual LST and variability than adjacent unburned forested areas, as a result of strong summer warming and weak winter cooling. A strong decrease in summer ET is the main mechanism for the increase in LST in burned forests. Additionally, the LST response is different between boreal forest types. Our results suggest that boreal forest fires result in increased surface warming primarily due to decreases in evaporative cooling in summer.