|Van Griensven, Ann - UNESCO-IHE WATER EDU INST|
Submitted to: Journal of Environmental Modeling and Software
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 11, 2007
Publication Date: October 24, 2007
Citation: Green, C.H., Van Griensven, A. 2007. Autocalibration in hydrologic modeling: Using SWAT2005 in small-scale watersheds. Journal of Environmental Modeling and Software. 23:422-434. Interpretive Summary: Agricultural-related activities can contribute to water quality impairment. This study uses the Soil and Water Assessment Tool (SWAT) model to identify the key parameters in the model that will impact the simulation results. In order to expedite the process of determining the most pertinent model parameters and the value ranges that represent real conditions at the study site, a tool has been embedded in the model. This study site has previously been modeled with SWAT and this portion compares the results of the previous model results to those with the new tool. The results showed that a combination of using the automated tool with user input had the best statistical results in predicting runoff, sediment, and chemical loss. This tool has proven that will adequate knowledge of the study site, the model simulation process can represent real conditions better and more quickly.
Technical Abstract: SWAT is a physically-based model that can simulate water quality and quantity at the watershed scale. Due to many of the processes involved in the manual or auto-calibration of model parameters and the knowledge of realistic input values, calibration can become difficult. An autocalibration-sensitivity analysis procedure was embedded in SWAT version 2005 (SWAT2005) to optimize parameter processing. This embedded procedure is applied to six small-scale watersheds (subwatersheds) in the Central Texas Blackland Prairie. The objective of this study is to evaluate the effectiveness of the autocalibration-sensitivity analysis procedures at small scale watersheds (4.0-8.4 ha). Model simulations are completed using two data scenarios: 1) one year used for parameter calibration; 2) five years used for parameter calibration. The impact of manual parameter calibration versus autocalibration with manual adjustment on model simulation results is tested. The combination of autocalibration tool parameter values and manually adjusted parameters for the 2000-2004 simulation period resulted in the highest ENS and R2 values for discharge; however, the same five year period yielded better overall ENS, R2 and p-values for the simulation values that were manually adjusted. The disparity is most likely due to the limited number of parameters that are included in this version of the autocalibration tool (i.e. Nperco, Pperco, and nitrate). Overall, SWAT2005 simulated the hydrology and the water quality constituents at the subwatershed-scale more adequately when all of the available observed data were used for model simulation as evidenced by statistical measure when both the autocalibration and manually adjusted parameters were used in the simulation.