The Soil & Water Assessment Tool (SWAT) is a river basin scale model developed to quantify the impact of land management practices in large, complex watersheds. SWAT is a public domain hydrology model with the following components: weather, surface runoff, return flow, percolation, evapotranspiration, transmission losses, pond and reservoir storage, crop growth and irrigation, groundwater flow, reach routing, nutrient and pesticide loading, and water transfer.
SWAT is a continuous time model that operates on a daily time step at basin scale. Its objective is to predict the long-term impacts of management and of the timing of agricultural practices within a year (i.e., crop rotations, planting and harvest dates, irrigation, fertilizer, and pesticide application rates and timing). It can be used to simulate at the basin scale water and nutrients cycle in landscapes whose dominant land use is agriculture. It can also help in assessing the environmental efficiency of best management practices and alternative management policies.
SWAT uses a two-level disaggregation scheme; a preliminary subbasin identification is carried out based on topographic criteria, followed by further discretization using land use and soil type considerations. Areas with the same topographic characteristics, soil type, land use and management form a Hydrologic Response Unit (HRU), a basic computational unit assumed to be homogeneous in hydrologic response to land cover change.
SWAT is a comprehensive watershed management model that encompasses several disciplines. We try to simulate the major components of these processes as simply and realistically as possible. Not only is the SWAT model complex, the inputs and outputs can also seem overwhelming at first. The SWAT development team tries to keep all inputs readily available, and supply required data for weather, soils, crops, pesticides and nutrients (for the U.S.). The SWAT development team has developed various interfaces to ease input development and appreciates any suggestions or bugs you may find in the interfaces. The SWAT user groups, including international user groups, provide a method to exchange your ideas and issues about the use of SWAT model with fellow SWAT model users. The SWAT development team monitors all messages posted to the user groups.