Numerical simulations of shallow groundwater flow and heat transport in continuous permafrost setting under impact of climate warming

摘要

Numerical simulations of coupled groundwater flow and heat transport are used to address how hydrogeological conditions can affect permafrost dynamics. The simulations are based on a two-dimensional vertical-plane conceptual model of a study site at the Iqaluit Airport, Nunavut, Canada, which includes a 50 in deep permafrost terrain with a shallow active layer, overlain by a paved taxiway with winter snow-covered embankments. Coupled groundwater flow and advective-conductive heat transport with freeze-thaw dynamics, temperature-dependent pore-water freezing functions, and latent heat are included in the model. The simulation results show that a smooth (low-slope) freezing function with a higher residual unfrozen moisture content produced a deeper thaw front compared to that using a steeper freezing function, generating a maximum increase in the depth to permafrost of 17.5 m after 268 years. Permafrost thaw rates in high-permeability zones within a heterogeneous system were also relatively higher compared to an otherwise equivalent homogeneous soil, resulting in a maximum increase of 2.6 in in the depth to permafrost after 238 years. As recharge water cools while flowing along the upgradient permafrost table, advectively driven heat transport is paradoxically shown to temporarily increase the height of the permafrost table in downgradient areas.