CLMT2 user's guide: A Coupled Model for Simulation of Hydraulic Processes from Canopy to Aquifer Version 1.0

CLMT2 is designed to simulate the land-surface and subsurface hydrologic response to meteorological forcing. This model combines a state-of-the-art land-surface model, the NCAR Community Land Model version 3 (CLM3), with a variably saturated groundwater model, the TOUGH2, through an internal interface that includes flux and state variables shared by the two submodels. Specifically, TOUGH2, in its simulation, uses infiltration, evaporation, and root-uptake rates, calculated by CLM3, as source/sink terms; CLM3, in its simulation, uses saturation and capillary pressure profiles, calculated by TOUGH2, as state variables. This new model, CLMT2, preserves the best aspects of both submodels: the state-of-the-art modeling capability of surface energy and hydrologic processes from CLM3 (including snow, runoff, freezing/melting, evapotranspiration, radiation, and biophysiological processes) and the more realistic physical-process-based modeling capability of subsurface hydrologic processes from TOUGH2 (including heterogeneity, three-dimensional flow, seamless combining of unsaturated and saturated zone, and water table). The preliminary simulation results show that the coupled model greatly improved the predictions of the water table, evapotranspiration, and surface temperature at a real watershed, as evaluated using 18 years of observed data. The new model is also ready to be coupled with an atmospheric simulation model, representing one of the first models that are capable to simulate hydraulic processes from top of the atmosphere to deep-ground.