Modeling Permafrost's Distribution and Prospective Development with Coupled Heat and Groundwater Flow Equation.

Abstract:

A need for improvements in numerical models for the representation of permafrost and active layer dynamics has been highlighted. Initial efforts to address this have been made, in particular by coupling heat and multiphase flow equations under transient conditions. Implications of honoring the physical representation of such process includes an improved ability to model and analyze effects of projected changes in hydro-climatic variables, as for example the change in thermal regime and the geographic patterns of permafrost degradation. In this contribution the recently developed frozen ground module of PFloTran for fully coupled transient heat and water flow under partially saturated conditions is applied to the subarctic field site of Tarfala in Northern Sweden, where the occurrence of permafrost is sporadic and strongly dependent on snow-depth. Optimizing this model to reproduce subsurface temperature fluctuations in the ground, as recorded in two different boreholes over the last decade, allows to identify the respective roles played by heat diffusion, advection and convection in a changing permafrost environment. The influence of topography is analyzed by applying the model to different domains geometries, where topography is simplified to different degrees. The model has been configured to reproduce temperature observations, providing a estimation of the distribution and thermal regime of permafrost over the entire hill-slope. Based on the configurations that give the most accurate validation against data, changes in permafrost are extrapolated by applying different scenarios of prospective climatic conditions.