SWAT Model Calibration, Validation and Parameter Sensitivity Analysis Using SWAT-CUP.

Calibration and validation of process-based hydrological models are two major processes while estimating the water balance components of watershed systems. The present study is carried out with an objective to develop a reliable hydrologic model simulating stream flow discharge with least uncertainty among the parameters chosen for calibration. Soil and Water Assessment Tool (SWAT, version 2012) model was used to simulate the stream flow of Skunk Creek (SK) watershed located in eastern part of South Dakota for the period from 1980-2000. Model calibration and validation were performed for both daily and monthly time periods using Sequential Uncertainty Fitting 2(SUFI-2, version 2) within SWAT- CUP using 24 parameters. Our calibration outputs for the period from 1987-1994 showed a good correlation between observed and model simulated values with NSE = 0.56 and R² = 0.70 for daily simulation. However, the model showed a better performance for monthly simulation with NSE and R² values of 0.84 and 0.84, respectively. During validation period (1995- 2000), the NSE and R² values were 0.44 and 0.55, respectively for daily simulation and these statistical values were 0.76 and 0.77, respectively for monthly time step. Following calibration, the overall effect of each parameter used was ranked using global sensitivity function in SWAT-CUP. From our analysis, the soil water capacity (SOL_AWC) and Initial SCS run off curve number for moisture condition II (CN2) were found to be the most sensitive parameters during two different iterations with different number of simulation but with the same inputs. The least sensitive parameter were found to be different in either cases unlike the most sensitive parameters. It was concluded that the complete know about of the hydrologic processes occurring within the watershed and awareness about acceptable meaningful range of the parameters is essential while developing reliable hydrologic model.