Boreal Forest Cover Delays Thermokarst Onset in Central Siberia's Yedoma Deposits

Abstract

Boreal forests, covering more than half of the world's permafrost, are essential for maintaining permafrost stability. However, climate change and forest shifts are threatening the delicate balance in the thermal equilibrium between the atmosphere, vegetation, and permafrost. We focus on Central Yakutia's ice-rich boreal regions, specifically two sites located in Spasskaya-Pad and Churapcha, to investigate the interplay of hydrothermal and climatic conditions that induce thermokarst. We employ a numerical permafrost model (CryoGrid), with a canopy model, and features for excess ground ice, lateral water flow and lake formation, to simulate the underlying physical processes under two forcing scenarios until 2060. The results reveal that forest delays the onset of thermokarst and ground ice melting by 3–18 years, depending on ice depth, climate forcing, and local conditions. Our simulations additionally reveal that a canopy slows excess ice melt by up to 7 years compared to bare ground simulations. Furthermore, in exceptionally warm and wet years, thermokarst initiation occurred rapidly in the bare ground simulations. In contrast, the canopy buffered against these conditions, suggesting that canopies might mitigate the impacts of small temperature and precipitation anomalies. This research highlights the critical role of forests in shaping the trajectory of thermokarst-related landscape transformations in ice-rich boreal permafrost regions. With the study region warming faster than average, forest cover transformations could significantly alter the hydrological balance. By integrating thermodynamics, hydrology, and ecology, our findings underscore the importance of forests in delaying thermokarst initiation and slowing ground ice melt, ultimately stabilizing permafrost ecosystems.