The Soil and Water Assessment Tool (SWAT) is a water quality model developed
by the Agricultural Research Service (ARS) to simulate runoff from agricultural
watersheds. In order to obtain the level of accuracy required for simulating the effect of
climate change on water quality in the runoff from northern and forested watersheds, a
number of modifications were made to the model. The crop growth submodel was
adapted to better represent forests, the snowmelt submodel was altered to improve the
prediction of spring runoff (without requiring more input data than the original snowmelt
submodel), and the evapotranspiration submodel was altered to more accurately simulate
the evaporation, or sublimation, of snow. An alternate submodel for calculating rates of
runoff and an alternate submodel for calculating percolation were also examined.
Furthermore, a number of bugs in the model code were corrected. The changes made and
the alternate submodels examined are described in this report. The changes made to the
model code, including the bug fixes, are listed in the appendix. Finally, the changes in
the simulations of water quality and quantity achieved by the model modifications are
compared to field data.
US Department of Agriculture, Grazingland Research Laboratory
Hanratty, Michael P.; Stefan, Heinz G..
Modifications of the Soil and Water . Assessment Tool (SWAT) for Application to Climate Change Studies.
St. Anthony Falls Laboratory.
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