Modeling Thermokarst Dynamics in Alaska Ecosystems

Ongoing climate change has implications for the stability and distribution of permafrost. Thermokarst results from changes in the surface thermal regime and expresses as the thawing of ice-rich permafrost and the associated subsidence of the surface. These changes can result in the transition of arctic and boreal ecosystems because of changes in hydrology and soil thermal dynamics. Such changes in the structure and function of arctic ecosystems have consequences for feedback pathways to the climate system including the exchange of water, energy, and carbon with the atmosphere. We present a conceptual state-and-transition model in arctic and boreal ecosystems of Alaska to predict how climate change may affect thermokarst dynamics across the landscape. The state-and-transition model includes several vegetation trajectories that can result from thermokarst disturbance. The model considers several factors in a hierarchical fashion to simulate thermokarst dynamics: predisposing factors, initiation factors, and expansion factors. Predisposing factors include topography, ground ice content and soil texture. Initiation factors include climate and fire. Expansion factors include climate and environmental conditions such as hydrology, erosion, soil texture and ice content. The model tracks thermokarst disturbance and associated vegetation transitions at 1km*1km resolution, and has been designed to be integrated into the Alaska Integrated Ecosystem Model (AIEM), which includes coupled models of fire disturbance, soil thermal dynamics, and ecosystem structure and function.