Simulating Hydrologic Interactions With a Model Formulation Based on DEM-Derived Surface Flow Paths and Boundary Condition-Resolved Exchange Fluxes (Invited)

A proper understanding and representation of the interactions between the different components of the hydrosphere (atmosphere, land surface, soil zone, aquifers) is increasingly relevant to climate prediction, environmental protection, and water management. There is a variety of models and modeling approaches currently in use to model atmosphere/surface/subsurface interactions. Rigorous testing of available models is extremely important, in particular with regards to how interactions are parameterized and how different processes (or process submodels) are integrated or coupled. The coupling term for the model tested in this work is computed as the balance between atmospheric forcing (rainfall and potential evaporation) and the amount of water that can actually infiltrate or exfiltrate the soil. Surface runoff is represented by a diffusion wave equation for both overland and channel flow, with the drainage network extracted from digital terrain data. Sensitivity tests, intercomparison studies, and other model applications are used to illustrate features and challenges for this particular model formulation, in relation to other approaches where relevant. Some of the validation challenges and other issues, for this and similar coupled hydrologic models, include grid resolution effects (are these models scale invariant?), observation/measurement difficulties (for rill or sheet flow land surface routing paradigms, for example), poorly-known behavior during evaporation/drying stages as compared to rainfall/infiltration periods (physics and numerics), and a possible bias to overestimation of near-surface soil moisture and groundwater levels (linked to the treatment of surface and other boundary conditions)