In semi-arid areas, the actual evapotranspiration (AET) can surpass the yearly precipitation levels, leading to potential risks for the hydrological budget and causing groundwater depletion. Despite numerous studies on AET, the contribution of various water sources to AET remains poorly understood at a regional scale. The HydroGeoSphere model (HGS) is a distributed process-based model that simulates various physical processes from surface to groundwater, including storage and variably-saturated soil/rock flow in the porous media domain, storage and runoff in the surface domain, and actual evapotranspiration from both domains. Nevertheless, the literature lacks an application of HGS for investigating evapotranspiration in various eco-hydro(geo)logical settings (EHG), including Mountains, Foothills, and Plains. We developed a high-resolution HGS model of North Saskatchewan River Basin (NSRB), a relatively large river basin in central Alberta, to study the spatiotemporal variability of surface and subsurface water resource contributions to AET across different EHGs.
Preliminary results suggest that AET accounts for 75% of annual precipitation, reaching its maximum water loss in the Foothills, followed by the Plains and Mountains. Mixed forest coverage experiences the highest AET/PCP rate of 90%, while Barren lands exhibit the lowest rate of 30%. Additionally, the porous media transpiration represents the largest water contribution (87%) to annual AET, followed by porous media evaporation (8%), demonstrating the importance of subsurface water, with surface evaporation making the minor contribution (5%).
This study highlights strength and limitations of HGS in simulation of AET and its water source accounting across EHGs and provides suggestions for improvements in future studies.