MODELING GROUNDWATER RECHARGE IN A CHANGING CRYOSPHERE (Invited Presentation)

Groundwater recharge mechanisms in seasonally frozen and permafrost landscapes are governed by interactions between snow and ground freeze-thaw processes that determine the timing, magnitude, and spatial distribution of recharge. Snowmelt-driven infiltration and recharge are complicated by coupled water and heat transport phenomena such as porewater freeze-thaw, cryo-suction, preferential flow, and the influence of surface water and energy balance processes during snowmelt. Simulation of these complex processes remains a major challenge, but as numerical models and computational capability continue to improve, physically-based descriptions and meaningful representations of these interacting processes have begun to be incorporated into various modeling frameworks.

This presentation discusses different approaches for simulating groundwater recharge in landscapes subject to snow and freeze-thaw processes. Modeling approaches vary from soil-water balance models, to single and dual-permeability Richards equation descriptions, to more complex fully-integrated surface water-groundwater models. Specific field and modeling examples from the seasonally frozen Canadian Prairies and the discontinuous permafrost zone in northern Canada are presented to demonstrate the importance of representing these processes when simulating recharge in cold regions, including the effects of vadose zone processes such as preferential flow, and surface processes such as changing vegetation and snowmelt dynamics. Results highlight that representing the interaction of these complex but important processes in modeling efforts can greatly improve our understanding of, and ability to simulate the effects of, snow and freeze-thaw on groundwater recharge in cold regions under changing climate, vegetation cover, and land use conditions.