Quantifying Changing Groundwater Exfiltration at a High Arctic Site due to Climate Change

ABSTRACT Increasing Arctic warming rates drive significant environmental change, including permafrost thaw and new groundwater pathway development, thereby increasing groundwater vulnerability to contaminant transport at the thousands of unremediated sites in the circumpolar north. As a first step in assessing hydrogeological controls of Arctic contaminant transport, this study uses numerical modelling to disentangle the impacts of increasing precipitation and air temperature on groundwater flow within the active layer at a high arctic site (63°30′ N). The study uses the numerical model SUTRA 4.0 to simulate groundwater flow and energy transport, including dynamic freeze–thaw processes, across an Arctic hillslope under current and future air temperatures due to climate warming. The model domain represents a two‐dimensional hillslope terminating in a lake. Two layers implemented in the model represent unconsolidated glacial till and underlying crystalline bedrock. Four simulation cases are examined based on downscaled CMIP5 projections under the high‐emissions “business as usual” scenario: Baseline Conditions (1981–2010), Near‐Projections (2011–2040), Mid‐Projections (2041–2070), and Far Projections (2071–2100). Climate projections indicate increasing mean annual air temperatures, reducing annual air temperature amplitude, and increasing precipitation. Further, model results show that groundwater flow dynamics are primarily influenced by the coupling of both increased mean annual temperatures and precipitation, with the consequent deepening and prolonged thawing of the active layer allowing for increased groundwater exfiltration to the lake. Sensitivity analysis identifies overburden permeability, overburden residual liquid freezing temperature, and model base temperature as significant parameters that affect model outcomes. Finally, a variable transmissivity assessment provides new insight into active layer groundwater flows.