Simulation results indicate that if a value of ESCO that was calibrated from the USAW data for winter wheat was applied at the watershed scale, it would lead to model simulations that give unrealistically high values of surface runoff.
This investigation accentuates some of the difficulties associated with relating point or USAW measurements to watershed scale applications.
Our objective was to determine whether or not model parameters that govern the surface runoff response in SWAT that were calibrated from rain-fed homogeneous, USAWs could be scaled up to provide accurate runoff simulations at a watershed scale that consisted of heterogeneous land cover, soils, and topographic features.
These USAWs consisted of homogeneous pasture and winter wheat cover types.
Use of the curve number method in turn facilitated the comparison of simulated runoff responses among the USAWs and subwatersheds, given the various land cover and soil features represented within the study area.
Table 1 lists the respective number of subbasins and HRUs that were delineated for each of the USAWs and subwatersheds within the LWREW Delineated HRUs were assumed to be spatially uniform in terms of soils, land use, topography, and climate data.
A noticeable difference between the USAWs and the subwatersheds delineated in this study was the size of the respective subbasins.
A similar procedure described above for the calibration of the USAWs was used to calibrate subwatersheds 483, 442, and 526.
A comparison of measured versus simulated average runoff, PBIAS, and NSE for each of the four LWREW USAWs and the three subwatersheds is presented in table 4.