Sensitivity analysis, calibration, and validations for a multisite and multivariable SWAT model

The ability of a watershed model to mimic specified watershed processes is assessed through the calibration and validation process. The Soil and Water Assessment Tool (SWAT) watershed model was implemented in the Beaver Reservoir Watershed of Northwest Arkansas. The objectives were to: (1) provide detailed information on calibrating and applying a multisite and multivariable SWAT model; (2) conduct sensitivity analysis; and (3) perform calibration and validation at three different sites for flow, sediment, total phosphorus (TP), and nitrate-nitrogen (NO3-N) plus nitrite-nitrogen (NO2-N). Relative sensitivity analysis was conducted to identify parameters that most influenced predicted flow, sediment, and nutrient model outputs. A multiobjective function was defined that consisted of optimizing three statistics: percent relative error (RE), Nash-Sutcliffe Coefficient (R-NS(2)), and coefficient of determination (R-2). This function was used to successfully calibrate and validate a SWAT model of Beaver Reservoir Watershed at multisites while considering multivariables. Calibration and validation of the model is a key factor in reducing uncertainty and increasing user confidence in its predictive abilities, which makes the application of the model effective. Information on calibration and validation of multisite, multivariable SWAT models has been provided to assist watershed modelers in developing their models to achieve watershed management goals.