A sensitivity analysis of the input parameters of the Soil and Water Assessment
Tool (SWAT), developed by the USDA Agricultural Research Service, was conducted.
The effects of input parameters describing watershed characteristics and land
management practices on SWAT results were analyzed using individual parameter
perturbation. The model outputs were monthly streamflow (mm) and monthly averages
for sediment yield (t/day), total phosphorus yield (kg/day), ammonia/organic N yield
(kg/day), and nitrate/nitrite yield (kg/day). The results were reported qualitatively, not
quantitatively, because of the large number of input parameters required for SWAT.
Streamflow was most sensitive to the SCS runoff curve number, sediment yield to
sediment routing parameters, total P and ammonia/organic N yields to land management
practices and to P and N concentrations in the top soil layer, and nitrate/nitrate yield to
concentrations in the top soil layer. The effects of input parameters describing climate.
conditions were analyzed using error analysis. The climate parameters were monthly
precipitation; monthly averages for maximum, minimum, and mean daily air temperature;
and monthly averages for relative humidity, solar radiation, and wind speed. SWAT was
run using historical weather data and modified historical weather data representing a
doubling of atmospheric CO2 concentration. The percent of the variations in the output
variables that were explained by the variations in the climate parameters were calculated.
Variations in precipitation and, when snowmelt was a significant part of the hydrologic
budget, in temperature explained the variations in the model output the most.
Grazing Land Research Laboratory, US Department of Agrictulture; Mid-Continent Ecology Division, US Environmental Protection Agency
Hanratty, Michael P..
Sensitivity Analysis of the Soil and Water Assessment Tool (SWAT) for Simulation of Climate Change Effects.
St. Anthony Falls Laboratory.
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