Evaluation of mixed forest evapotranspiration and soil moisture using measured and swat simulated results in a hillslope watershed

This study evaluated SWAT model when measured Evapotranspiration (ET) and Soil Moisture (SM) in addition to streamflow (Q) data were used to calibrate the simulated values in a 8.54 km2 hillslope watershed of South Korea. By using 7 years (2003–2009) daily Q at the watershed outlet, 3 years (2007–2009) daily ET and SM data measured in the mixed forest, the SWAT model was calibrated and validated with the average Nash-Sutcliffe model efficiency (E) for Q of 0.76, and the coefficient of determination (R2) for SM and ET of 0.55 and 0.59, respectively. The use of measured hydrological state variables such as ET or SM in SWAT modeling provided more reliable interpretation of model parameters by inducing the reduction of parameter uncertainty and understanding the behavior of the watershed water balance. When the watershed has only Q data for model calibration, it is encouraged to consider soil (ESCO) and plant related parameters (EPCO and CANMX) in addition to surface runoff (CN2, and Surlag) and groundwater related parameters (GW_ DELAY and GW_ REVAP).