Modelling the impacts of climate change on groundwater: A comparative study of two unconfined aquifers in southern British Columbia and northern Washington State

A methodology is developed for linking climate and groundwater models to investigate future impacts of climate change on groundwater resources using two case study sites of unconfined aquifers in southern British Columbia and northern Washington State. One semi-arid site is compared with one wet coastal site. The two groundwater systems differ in river-aquifer interactions, recharge, aquifer heterogeneity, scale, and groundwater use. Climate change scenarios from the Canadian Global Coupled Model 1 model runs for 1961-2000,2010-2039,2040-2069 and 2070-2099 are downscaled to local conditions, modelled at daily time scales using a stochastic weather generator, and applied to the spatially-distributed infiltration model. At one site the basin-scale runoff is also downscaled to predict river discharge and river-aquifer interactions in future climates. The impacts of predicted climate change on the groundwater system for each site are modelled in three-dimensions using Visual MODFLOW. Results and methodologies are compared and discussed.