Effect of different topographic data sources on soil loss estimation for a mountainous watershed in Northern China

The effect of topography on soil loss can be characterized by slope length and slope steepness factors. These factors are commonly evaluated using digital elevation models (DEM) which can be generated from a large variety of topographic data. The purpose of this study was to evaluate the effect of topographic data source on estimated soil loss for a mountainous watershed. The Dongtaigou watershed (90 ha) is located in Huairou District, Beijing, China. Data sources included topographic maps at 1:2000, 1:10,000, and 1:50,000 scales, and 30-m DEM from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) Global Digital Elevation Map (GDEM) dataset. The grid sizes considered were 2, 5, 10, 25, and 30 m. The results showed that the calculated average slope steepness and soil loss were reduced and the average slope length increased when the map scale was decreased. With results using 1:2000 map and 2-m grid as the reference, the land area with minimal soil loss (<2 t ha⁻¹ year⁻¹) was 5.7 ha, and the area with moderate soil loss (2–25 t ha⁻¹ year⁻¹) was 77.9 ha. Compared to these reference values, the 1:10,000 map would bring out a 42 % increase in the area with minimal soil loss, and a concurrent decrease of −8 % in the area with a moderate soil loss. For the 30-m ASTER GDEM V1, the calculated slope steepness is some 64 % lower than the reference value. The slope length, on the other hand, was increased by 265 % and soil loss decreased by 47 % in comparison with the reference values. For all map scales and grid sizes, the relative errors in the estimated soil loss were about 50 % of the relative errors in slope steepness.