Uncertainty of SWAT model at different DEM resolutions in a large mountainous watershed

• The sensitivity of DEM resolutions on H/NPS modeling in a large mountainous watershed was analyzed.
• The uncertainty of DEM resolutions on temporal distribution of H/NPS indicators were examined.
• The optimal DEM resolutions for H/NPS indicators modeling were identified.

The objective of this study was to enhance understanding of the sensitivity of the SWAT model to the resolutions of Digital Elevation Models (DEMs) based on the analysis of multiple evaluation indicators. The Xiangxi River, a large tributary of Three Gorges Reservoir in China, was selected as the study area. A range of 17 DEM spatial resolutions, from 30 to 1000 m, was examined, and the annual and monthly model outputs based on each resolution were compared. The following results were obtained: (i) sediment yield was greatly affected by DEM resolution; (ii) the prediction of dissolved oxygen load was significantly affected by DEM resolutions coarser than 500 m; (iii) Total Nitrogen (TN) load was not greatly affected by the DEM resolution; (iv) Nitrate Nitrogen (NO3–N) and Total Phosphorus (TP) loads were slightly affected by the DEM resolution; and (v) flow and Ammonia Nitrogen (NH4–N) load were essentially unaffected by the DEM resolution. The flow and dissolved oxygen load decreased more significantly in the dry season than in the wet and normal seasons. Excluding flow and dissolved oxygen, the uncertainties of the other Hydrology/Non-point Source (H/NPS) pollution indicators were greater in the wet season than in the dry and normal seasons. Considering the temporal distribution uncertainties, the optimal DEM resolutions for flow was 30–200 m, for sediment and TP was 30–100 m, for dissolved oxygen and NO3–N was 30–300 m, for NH4–N was 30 to 70 m and for TN was 30–150 m.

The sensitivity of monthly flow, sediment, dissolved oxygen, NH4–N, NO3–N, TN and TP modeling results of SWAT in 2002–2006 based on a range of 17 DEM spatial resolutions (from 30 to 1000 m), was examined, with considered the uncertainty of temporal distribution. All of them were affected by DEM resolution to various degrees.Figure optionsDownload high-quality image (164 K)Download as PowerPoint slide