Hydrologic Calibration and Validation of SWAT in a Snow-Dominated Rocky Mountain Watershed, Montana, U.S.A.1

Authors

  • Robert S. Ahl,

    1. Adjunct Professor, Department of Forest Management, College of Forestry and Conservation, The University of Montana, 32 Campus Drive., Missoula, Montana 59812
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  • Scott W. Woods,

    1. Associate Professor, Department of Ecosystem Sciences and Conservation, College of Forestry and Conservation, The University of Montana, Montana
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  • Hans R. Zuuring

    1. Chair, Department of Forest Management, College of Forestry and Conservation, The University of Montana, Montana.
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  • 1

    Paper No. JAWRA-07-0151-P of the Journal of the American Water Resources Association (JAWRA). Discussions are open until February 1, 2009.

(E-Mail/Ahl: rob.ahl@umontana.edu)

Abstract

Abstract:  The Soil and Water Assessment Tool (SWAT) has been applied successfully in temperate environments but little is known about its performance in the snow-dominated, forested, mountainous watersheds that provide much of the water supply in western North America. To address this knowledge gap, we configured SWAT to simulate the streamflow of Tenderfoot Creek (TCSWAT). Located in central Montana, TCSWAT represents a high-elevation watershed with ∼85% coniferous forest cover where more than 70% of the annual precipitation falls as snow, and runoff comes primarily from spring snowmelt. Model calibration using four years of measured daily streamflow, temperature, and precipitation data resulted in a relative error (RE) of 2% for annual water yield estimates, and mean paired deviations (Dv) of 36 and 31% and Nash-Sutcliffe (NS) efficiencies of 0.90 and 0.86 for monthly and daily streamflow, respectively. Model validation was conducted using an additional four years of data and the performance was similar to the calibration period, with RE of 4% for annual water yields, Dv of 43% and 32%, and NS efficiencies of 0.90 and 0.76 for monthly and daily streamflow, respectively. An objective, regression-based model invalidation procedure also indicated that the model was validated for the overall simulation period. Seasonally, SWAT performed well during the spring and early summer snowmelt runoff period, but was a poor predictor of late summer and winter base flow. The calibrated model was most sensitive to snowmelt parameters, followed in decreasing order of influence by the surface runoff lag, ground water, soil, and SCS Curve Number parameter sets. Model sensitivity to the surface runoff lag parameter reflected the influence of frozen soils on runoff processes. Results indicated that SWAT can provide reasonable predictions of annual, monthly, and daily streamflow from forested montane watersheds, but further model refinements could improve representation of snowmelt runoff processes and performance during the base flow period in this environment.

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