ADAPTING GROUNDWATER MODEL BOUNDARY CONDITIONS FOR COLD REGIONS (Invited Presentation)

Numerical groundwater models have been used for many decades to understand subsurface hydrology and to simulate future and current groundwater dynamics. However, most of these models are not adapted to cold regions. In these environments, the storage and movement of groundwater is affected by permafrost that confines groundwater flow to unfrozen zones of the ground. Permafrost thaw can greatly increase subsurface hydraulic conductivity and hydrological connectivity between aquifers and surface water bodies. New groundwater modelling tools that simulate groundwater flow and energy transport, including freezing and thawing processes, have recently been developed to better understand the impacts of climate change and permafrost thaw on northern hydrology. To date, these models have only been used by a few research groups and have not been widely used for managing cold regions groundwater resources.

Compared to groundwater models that only simulate groundwater flow, these cold regions models are difficult to calibrate and replicate field data. One of the biggest challenges is to design land-surface boundary conditions. Processes such as snow insulation, snowmelt, and seasonal freezing and limited applicable field data make the accurate representation of this boundary challenging. Herein, we apply different sets of thermal and hydraulic surface boundary conditions adapted for cold regions to assess their impact on model outcomes, such as active layer thickness, permafrost thawing rate, and spatial and seasonal patterns groundwater discharge rate to the land surface. We test and compare the sensitivity of model outcomes to these boundary conditions in different settings. From these analyses, we evaluate the boundary conditions that exert the largest influence on model outcomes and provide recommendations for which boundary conditions to use depending on the setting. This study provides guidelines to develop effective conceptual and numerical groundwater models in cold regions.