Assessment of Soil Erosion from an Ungauged Small Watershed and Its Effect on Lake Ulansuhai, China

Lake Ulansuhai, one of the main water sources for semi-arid areas of China, has a local deposit caused by soil erosion during past decades. However, a lack of monitor stations prevents better estimation of soil erosion levels. Therefore, we try to estimate soil erosion in the Huangtuyaozi (HTYZ) watershed, an ungauged small watershed of the lake’s eastern watershed, by using the revised universal soil loss equation (RUSLE) model and multi-source remote sensing data, and analyze its key drivers and effect on the lake siltation. The result showed that the soil erosion rate in the HTYZ watershed ranged from 0 to 129.893 t ha⁻¹ yr⁻¹ with an average of 6.45 t ha⁻¹ yr⁻¹ during 1986–2015. In particular, 80.06% of the area was less than 10 t ha⁻¹ yr⁻¹, and just 0.06% was over 50 t ha⁻¹ yr⁻¹, mainly in the mountain area, the southern part of the HTYZ watershed. Moreover, rainfall erosivity factor is the key factor, and rainfall during flood season plays a key role in soil erosion. Due to the soil erosion of HTYZ, siltation in Lake Ulansuhai reached 223.83 ha, with the annual siltation area increasing at a rate of 7.46 ha/yr. The results could provide a reference for estimating soil erosion of ungauged small watershed in semi-arid areas.