Effect of Watershed Subdivision on SWAT Modeling with Consideration of Parameter Uncertainty

Parameterization is crucial for the soil and water assessment tool (SWAT) before applying it to simulate hydrology, soil erosion, and nonpoint source pollution. Accordingly, parameter uncertainty should be considered during watershed delineation. In this study, the Upper Daning River Watershed was delineated into different numbers of subwatersheds under various delineation schemes by changing the threshold drainage area (TDA). All schemes were then parameterized and SWAT was run to determine which scheme had the highest modeling efficiency. Results indicate that the simulation under the finest delineation scheme was not the most accurate but moderate level delineation scheme with TDA of 5,000 ha was. Then the parameter uncertainty introduced by model calibration was explained by the coverage of observed data and the width of the 95% prediction band (P-factor and R-factor). To further investigate the effect of changing the TDA on SWAT modeling, the best fit set of parameter values of the delineation scheme with TDA of 5,000 ha was extended to the other schemes, but the results revealed only slight differences.