Implementation of a Root Water Extraction Module in CATHY: Comparison of Four Empirical Root-density Distribution Models

A root water-extraction module was incorporated into CATHY, a coupled surface-subsurface flow, physically-based, distributed hydrological model, to account for transpiration of annual crops. Four empirical vertical root-density distribution models were used to evaluate the effect of plant transpiration on tile-drain flow and edge-of-field flow. Model 1 uses a uniform distribution for the entire root zone; Model 2, a nonlinear root density distribution function; and Models 3 and 4, two configurations of exponential root water uptake distribution. When comparing simulation results with and without a root water extraction module, we observed that Model 1 produces reasonable reductions in tile-drain and edge-of-field flows. Further analysis indicates that edge-of-field flow is more affected by the root water extraction module than tile-drain flow. Therefore, as the unsaturated zone increases, edge-of-field flow decreases more than tile-drain flow.