Analyses of DEM Resolution on SWAT-simulated Stream Flow in Qihe Watershed

Resolution of data is a sensitive issue in hydrological modeling. The sensitivity of stream flow simulated with the Soil and Water Assessment Tool (SWAT) model to Digital Elevation Model (DEM) resolution has been partially understood. However, few studies on the effect of the influence of DEM with resolution over 20 m on daily runoff modeling. The objective of this study was to enhance understanding the impact of DEM (from 8 m to 900 m) within the SWAT model to simulate runoff on annual, monthly and daily scale. The Qihe river, one of the headwaters of Danjiangkou reservoir, was selected as the study area. The key findings were as follows: (1) As DEM resolution becomes coarser, the extracted land form tends to be flat, and the total area of watershed, maximum elevation, and maximum slope generally show a decreasing trend, while the minimum elevation and minimum slope show an increasing trend. (2) The DEM resolution directly affect the water generation and concentration, the increase of DEM mesh size would result in homogenization of simulated stream flow and flood peak attenuation. (3) When DEM resolution is higher than 30 m, the simulated annual and monthly runoff remain unchanged, but the simulated daily runoff will be different very much. The higher the resolution is, the better the simulation results will be, especially for the simulation of flood peak. Therefore, a DEM with higher resolution can describe the runoff process more precisely.