Evaluating Integrated Surface/Subsurface Permafrost Thermal Hydrology Models Against Field Data in Polygonal Tundra

Numerical simulations are essential tools for understanding the complex hydrological response of Arctic regions to a warming climate. However, strong coupling among thermal and hydrologic processes on the surface and in the subsurface and the significant role that subtle variations in surface topography have in regulating flow direction and surface storage lead to significant uncertainties. Careful model evaluation against field observations is thus important to build confidence. Here, we evaluate the integrated surface/subsurface permafrost thermal hydrology models in the Advanced Terrestrial Simulator (ATS) against field observations in polygonal tundra at the Barrow Environmental Observatory. ATS represents important physical process such as lateral surface and subsurface flows, advective heat transport, cryosuction, and coupled surface energy balance. We simulated thermal hydrology of three-dimensional ice-wedge polygons with generic but broadly representative surface microtopography. We drove the simulations with meteorological data and observed water table elevations in ice-wedge polygon troughs, and compared simulated water table elevations in the polygon centers to observed values. The simulated soil temperatures at several depths were also compared with multiyear high-frequency observed data. The simulations were found to be sensitive to parameters in the bare soil evaporation model, snowpack, and the soil horizontal hydraulic conductivity. With limited calibration of the soil properties and evaporation model parameters, the simulations were found to be consistent with observed water tables, active layer thickness, snowpack depth, evaporation, and observed soil temperatures at several depths in trough, rim, and center. The study builds confidence in the emerging class of integrated surface/subsurface permafrost simulators and provides a optimized set of model parameters for use in projections of permafrost dynamics in a warming climate.