Improved representation of surface‐groundwater interaction in the Canadian land surface scheme

Abstract

The improvement of surface‐groundwater interactions in land surface models are necessary to determine the evolution of hydrologic variables such as surface runoff, evapotranspiration, soil moisture, and streamflows, especially during dry conditions, when streamflows are largely derived from water releases from groundwater storage. Despite its importance, investigations of the effects of surface‐groundwater interactions on streamflows simulated by large‐scale land surface models are lacking. In this paper, we implement a new parameterization to represent groundwater dynamics in the Canadian Land Surface Scheme (CLASS), which is used for modelling the land surface component in the Canadian regional and global climate models. We compare offline simulations performed with the original and modified versions of CLASS to find the impact of these modifications on the regional hydrology. The offline simulations are driven by ERA‐Interim atmospheric forcing data from the European Centre for Medium‐Range Weather Forecasts reanalysis (for the 1980–2011 period), over a northeast Canadian domain. The original and modified versions of CLASS differ in the soil bottom boundary conditions, with free (gravitational) drainage in the former, while an unconfined aquifer at the depth of bedrock is considered in the latter. Results suggest higher soil moisture levels in the simulation with modified CLASS compared to the original version, particularly for regions with shallow water table. At these locations, summer surface runoff, evapotranspiration and streamflows are also higher in the simulation with modified CLASS, and the simulated low flow values are in better agreement to those observed. This study thus demonstrates the need to account for surface‐groundwater interactions in land surface models for realistic simulation of hydrological processes and streamflows.