Model Library
Soil and Water Assessment Tool (SWAT)
Model name: Soil and Water Assessment Tool (SWAT)
Developed by: U.S. Department of Agriculture (USDA) Agricultural Research Service (ARS) and Texas A&M scientists (Last update: 2023)
Model type: Quasi-dynamic, semi-distributed, deterministic, process-based, ecohydrological small watershed to river basin-scale model
Computational requirements: 32-bit and 64-bit Windows, Linux, approx. 2–5 GB for software installation and input data, Ensure compatibility with other software components.
Software requirements: GIS (required): ArcSWAT, QSWAT, Mapwindow, AVSwat-X, GRASS;
Calibration tool: SWAT-CUP
Capabilities and Limitations:
Capabilities
- Most common-used watershed model;
- Comprehensive environmental modeling software;
- Handling large watersheds with complex hydrology;
- Simulating up to continental scale without requiring excessive data and calibration;
- It can simulate sediment and nutrient load reductions by management practices;
- Supported by extensive documentation.
Limitations
- Low prediction accuracy in simulating areas with serious snow cover (Costa et al., 2019);
- It does not incorporate bacterial growth (Cho et al., 2020) and metals reactions (Zouiten et al., 2013);
- Not well-suited to simulate sub-daily events and seasonal dynamics of sediment load delivery at a small catchment outlet (Rhomad et al., 2023);
- Low temporal resolution (Duku et al., 2015; Akoko et al., 2021);
- Require numerous input data (Akoko et al., 2021);
- SWAT was not designed to model heterogeneous mountain basins (Fontaine et al., 2002);
- It simplifies the cross-section of natural channels and rivers to be a trapezoid or rectangular (Borah et al., 2019);
- Lack of baseflow maintenance during low flow periods (Sánchez-Gómez et al., 2024).
Model Inputs and Outputs:
Inputs
- Required: Topography data, LULC data, Soil data, Meteorological data, Hydrological data, Water quality data, Management data.
- Optional: Stream network, Soil moisture, Climate statistics, Crop data, Pesticides, Waterbody management, Aquifer data, Floodplain.
Outputs
- Reports of time-series simulations of hydrological and water quality loadings in watershed(s).
- Soil moisture, crop yields, and irrigation simulations.
- Reservoir storage, channel flow simulations.
Examples:
References
Rath, S., Zamora-Re, M., Graham, W., Dukes, M., & Kaplan, D. (2021). Quantifying nitrate leaching to groundwater from a corn-peanut rotation under a variety of irrigation and nutrient management practices in the Suwannee River Basin, Florida. Agricultural Water Management, 246, 106634. https://doi.org/10.1016/j.agwat.2020.106634
Abimbola, O., Mittelstet, A., Messer, T., Berry, E., & van Griensven, A. (2021). Modeling and prioritizing interventions using pollution hotspots for reducing nutrients, atrazine, and E. coli concentrations in a watershed. Sustainability, 13(1), 103. https://doi.org/10.3390/su13010103
Objectives
The objectives of the study were: (1) Calibrate SWAT using observations from a three-year irrigation and N fertilizer rate management experiment for a corn peanut rotation conducted in Live Oak, Florida (Zamora et al., 2018, 2020); (2) evaluate the long-term effects of the experimental irrigation and fertilization treatments on annual yield, N uptake, irrigation applied, and NO₃-N leaching using calibrated parameters over a 39-year (1980–2018) historic weather record; (3) estimate the effect of planting a rye cover crop on NO₃-N leaching, irrigation water use, and yield in corn-peanut rotations.
The objectives of the study were: (1) simulate BMPs proposed by the Nebraska Department of Environment and Energy (NDEE) within target sub-watersheds to determine reductions in pollutant loads and (2) determine if water-quality standards are met at the watershed outlet.