Effect of DEM data resolution on SWAT output uncertainty

This paper describes the effect of DEM data resolution on predictions from the SWAT model. Measured hydrologic, meteorological, watershed characteristics and water quality data from Moores Creek watershed (near Lincoln, AR, USA) were used in the simulation. The effect of input data resolution was evaluated by running seven scenarios at increasing DEM grid sizes (30 ð 30 m, 100 ð 100 m, 150 ð 150 m, 200 ð 200 m, 300 ð 300 m, 500 ð 500 m, 1000 ð 1000 m). The model was calibrated on an annual basis for flow, NO3-N and total P using 30 ð 30 m DEM data. The predicted output at the calibrated scale was used to evaluate output accuracy for the remaining input resolutions. Results of this study showed that DEM resolution affects the watershed delineation, stream network and sub-basin classification in the SWAT model. A decrease in DEM resolution resulted in decreased stream flow and NO3-N load predictions. However, model predicted total P did not always decrease with DEM resolution. Results of this study indicate that the choice of input DEM resolution depends on the watershed response of interest. Minimum DEM data resolution ranged from 100 to 200 m to achieve less than 10% error in SWAT output for flow, NO3-N and TP predictions. Copyright  2005 John Wiley & Sons, Ltd.