The Soil and Water Assessment Tool (SWAT) is a deterministic continuous-time semi-distributed hydrological model for application at the river basin scale. The model was developed by the USDA Agricultural Research Service in the early 1990s based on Simulator for Water Resources in Rural Basins (SWRRB) and including routing procedures from Routing Outputs To Outlet (ROTO) tool (Arnold et al. 1995, 1998). SWAT is initialized by spatially distributed data on topography, land use/land cover, soils, land management and climate. The spatial disaggregation scheme includes subbasins delineated based on topography, which are further subdivided into nonspatial hydrological response units using the principle of similarity. Several versions of GIS interface were developed for SWAT enabling the model parametrization and initialization from maps and related data, starting from a GRASS GIS version (Srinivasan and Arnold 1994) to the current ArcGIS 10.1/10.2.2 interface version. From the early ...
