SWAT: Model use, calibration, and validation

Authors: Arnold, Jeffrey; Moriasi, Daniel; GASSMAN, PHILIP - Iowa State University; ABBASPOUR, KARIM - Swiss Federal Institute; White, Michael; SRINIVASAN, RAGHAVAN - Texas Agrilife Research; SANTHI, CHINNASAMY - Texas Agrilife Research; Harmel, Daren; VAN GRIENSVEN, ANN - United Nations Educational, Scientific And Cultural Organization (UNESCO); VAN LIEW, MICHAEL - University Of Nebraska; KANNAN, NARAYANAN - Texas Agrilife Research; JHA, MANOJ - North Carolina Agricultural And Technical State University

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/1/2012
Publication Date: 8/1/2012
Citation: Arnold, J.G., Moriasi, D.N., Gassman, P.W., Abbaspour, K.C., White, M.J., Srinivasan, R., Santhi, C., Harmel, R.D., Van Griensven, A., Van Liew, M.W., Kannan, N., Jha, M.K. 2012. SWAT: Model use, calibration, and validation. Transactions of the ASABE. 55(4):1491-1508.

Interpretive Summary: The SWAT (Soil and Water Assessment Tool) model is routinely used around the world to determine the impacts of land management and climate change for developing environmental and conservation policy. Before the model can be used to examine potential land management scenarios to mitigate pollution, it must be calibrated to measured flow and pollutant data to ensure accurate results. In the calibration procedure, model inputs are adjusted to match the measured data. Calibration is difficult since SWAT is a comprehensive watershed model requiring detailed inputs on climate, topography, soils, and land use. In this paper, the current state-of-the-art in calibration of SWAT is discussed including the use of automated genetic algorithms. Future research needs are discussed that include accounting for multiple hydrologic processes, spatial resolution, and uncertainty in the calibration process. Improved calibration methods will increase our confidence in model results and in setting appropriate conservation policy.

Technical Abstract: SWAT (Soil and Water Assessment Tool) is a comprehensive, semi-distributed river basin model that requires a large number of input parameters which complicates model parameterization and calibration. Several calibration techniques have been developed for SWAT including manual calibration procedures and automated procedures using the shuffled complex evolution method and other common methods. In addition, SWAT-CUP was recently developed and provides a decision making framework that incorporates a semi-automated approach (SUFI2) using both manual and automated calibration incorporating sensitivity and uncertainty analysis. In SWAT-CUP users can manually adjust parameters and ranges iteratively between autocalibration runs. Parameter sensitivity analysis helps focus the calibration, and uncertainty analysis is used to provide statistics for goodness-of-fit. The user interaction or manual component of the SWAT-CUP calibration forces the user to obtain a better understanding of the overall hydrologic processes (e.g., base flow ratios, ET, sediment sources and sinks, crop yields, and nutrient balances) and of parameter sensitivity. It is important for future calibration developments to spatially account for hydrologic processes; improve model run time efficiency; include the impact of uncertainty in the conceptual model, model parameters, and measured variables used in calibration; and assist users in checking for model errors. When calibrating a physically-based model like SWAT, it is important to remember that all model input parameters must be kept within a realistic uncertainty range and that no automatic procedure can substitute for actual physical knowledge of the watershed.