Quantifying the Impacts of Wildfires on Permafrost, Hydrology, and Carbon Dynamics in Northern High Latitudes

Wildfires drastically affect boreal forest ecosystem dynamics. Impacted higher plants, mosses and soil surface influence soil thermal and hydrological dynamics as well as carbon cycling. This study uses a process-based biogeochemistry model to evaluate how wildfires affect these dynamics using satellite-based fire severity data in northern high latitudes for the last few decades. We find that, in these regions, both burn areas and severity generally increase. In northern North America, forest wildfires remove ecosystem carbon of 2.4 Pg C and reduce net ecosystem production (NEP) from 32.6 to 0.8 Tg C yr⁻¹, as a result, the forest ecosystems lose 3.5 Pg C, shifting a carbon sink to a source from 1986 to 2020. For Northern Eurasia during 2003–2016, our model simulations indicate that fires increase soil temperature by 0.2–0.5 °C by reducing vegetation canopy, ground moss and surface soil organic matter, especially in Asian part of the region. Wildfires also increase water runoff by 131 million m³ yr^-1 by reducing evapotranspiration due to canopy loss, leading to a higher regional river discharge. Carbon combustion emissions are 1.7 Pg C in this period and regional NEP decreases from 106.4 to 66.1 Tg C yr^-1. Overall, the forest ecosystems lose 2.3 Pg C, shifting from a carbon sink to a source in northern Eurasia. Our study highlights the importance to consider wildfire burn area and severity effects in quantifying soil thermal, hydrological, and carbon dynamics in boreal forest ecosystems.