Sensitivity of Modeled Watershed Attributes and Hydrological Outputs to DEM Spatial Resolution

Abstract

A Digital Elevation Model (DEM) is a critical component for the parameterization of process-based watershed simulation models. The DEM is used to determine watershed attributes such as sub-basin extents and stream network topology, as well as to determine various topographic parameters, such as slope and aspect, that are used within various model computations. It is well known that the determination of watershed attributes and topographic parameters are affected by both the spatial resolution and accuracy of the DEM. For example, average terrain slope tends to increase as DEM resolution becomes increasingly fine (Zhang and Montgomery,1994). Therefore, variations in DEM resolution, and DEM errors, will propagate through the watershed modeling process and will influence resulting hydrological and water quality outputs (Chaubey et al., 2005). However, the influence of DEM resolution and accuracy is typically given little consideration within watershed modeling studies. Publically available DEMs (often with spatial resolutions of ~10-30 m) are easily accessible and typically free, and have been commonly used within watershed modeling studies. Recent developments in remote sensing technologies have made it possible to generate finer scale DEMs (down to 1 m resolutions), and it is anticipated that watershed modelers will have more opportunity to use these DEMs for model parameterization. This research focuses on the effects of varying the spatial resolution of fine scale DEMs on the determination of watershed attributes and topographic parameters, and the propagation of these variances into hydrological outputs from SWAT (Soil and Water Assessment Tool), a process-based watershed model. The study was conducted using DEMs that possessed varying spatial resolutions, but a consistent level of accuracy, in order to isolate only the effect of spatial resolution.