Soil erosion in the Three Gorges Reservoir area

Spatial and temporal change in soil erosion in the Three Gorges Reservoir area since the water storage of the reservoir began filling to 135m in 2003 is poorly understood. Using a modified soil erosion model, this study quantifies and analyses change in the extent and intensity of soil erosion in the region from 2000 to 2008. MODIS-NDVI remote sensing data (with 250m spatial resolution) are used in the modelling and analysis of the study. The total amount, area, and intensity of soil erosion in the reservoir region presented a declining trend from 2000 to 2008. Yet there was an anomaly in the trend, in which extreme soil erosion occurred in 2003 and lasted until 2005. The average volume of soil erosion per year decreased by 4.10106t and the mean area of land experiencing soil erosion reduced by 1129.6km2 from the pre-storage period (200002) to post-storage period II (200608). Land suffering soil erosion at high, very high, and severe levels mainly comprises forest and cropland on slopes with gradients 15 and is largely distributed in the eastern and south-western sections of the reservoir area. Land experiencing soil erosion at slight or moderate levels mainly involves cropland and forest on slopes with gradients 10 in the central section of the reservoir area. The impact of the Three Gorges Project on soil erosion since 2000 has been mainly mediated through three mechanisms: near-resettlement of rural and urban people; increased frequency and severity of geological hazards induced by rising storage of the reservoir; and implementation of ecological projects in the region. Through the former two mechanisms, soil erosion in the affected communities has been exacerbated, while the ongoing ecological projects appear to offset both the extent and intensity of soil erosion in the reservoir region. Other important factors influencing soil erosion include urban reconstruction and expansion, varying intensity of precipitation, and soil degradation.