NUMERICAL SIMULATIONS OF COUPLED GROUNDWATER FLOW AND HEAT TRANSPORT INCORPORATING FREEZE/THAW CYCLES AND PHASE CHANGE IN A CONTINUOUS PERMAFROST ENVIRONMENT

ABSTRACT: This study presents a series of numerical simulations to investigate the factors that control permafrost freezing and thawing in the shallow soil zone of the continuous permafrost environment at the Iqaluit Airport in Nunavut, Canada. A simplified conceptual model is first developed to represent the groundwater flow and thermal regime of the soil column and future climate scenarios are prepared based on those proposed by the IPCC (Intergovernmental Panel on Climate Change). A numerical model is then calibrated against ground temperatures. The calibrated model produced an excellent match with observed data and the mean absolute error is estimated to be 0.64 ˚C, which is 1.6% of the maximum temperature range. Numerical simulations reveal that under climate warming, conductive heat transport is the main driver for permafrost degradation at this site and that advective heat transport plays a minor role. This result can be attributed to the thaw front not migrating deeply enough into the ground to allow significant flow to develop and to the significant extent of low-permeability soil close to surface, which decreases the rate of flow and reduces the possible effects of thaw driven by advection.