| Dingxi City in Gansu Province belongs to Longxi Loess Plateau, and the land suffers from varying degrees of soil erosion due to impact of climate, hydrology and geology and other natural factors as well as of irrational development and utilization of human. To keep abreast of the development trend of soil erosion is the basic premise of establishment and implementation of ecological construction and environmental policies. Based on the remote sensing images, rainfall, topography and soil data in the objective area, the study investigated the spatial and temporal distribution patterns and variation of soil erosion in the past 16 years by using of GIS, RUSLE model, gave a quantitative estimation to the amount of soil erosion, and classified the soil erosion intensity in accordance with the "water erosion intensity classification standard" specified by Ministry of Water Resources. In the quantitative estimation of soil erosion, remote sensing data was used to get vegetation and land use information of soil erosion and extract vegetation and man-made factors of measures; rainfall data collected in the local area and soil data was used to calculate the rainfall erosivity and soil erodibility factor; elevation lines and elevation points were extracted through digital topographic maps, and digital elevation model (DEM) was established to obtain the slope and slope length factor in the area, and regional soil erosion model was set up to calculate the modulus of yearly soil erosion for each pixel individually through the various factors and monitoring model computation formula and to make a quantitative estimate on the soil erosion of the study area. 3S technology was used as the core technology, dynamic land degradation was carried out on land use, land-cover change and soil erosion, through series of studies, the following conclusions were obtained:1. Soil erosion intensity classification map generated in Anding District in Dingxi city clearly shows: in 12 years in 1993 -2005, slight erosion, moderate erosion has a net increase of 147.11 km~2 and 1418.91 km~2 respectively with increase rate of 4.05% and 39%, while the area that suffers from intense and extremely intense erosion was reduced, the net reduction is 575.56km~2 and 799.8 km~2,with the rate of 21.98% and 15.83%, indicating that the new moderate erosion mainly transformed from intense erosion and extremely intense erosion, indicating that all levels of erosion are turning towards the positive direction, and soil and water loss is getting better. Intense erosion and extremely intense erosion in 2005 occurred mainly in the northern high hilly areas with gully erosion, due to the region of ecological engineering is small, and coupled with interaction of natural factors and man-made destruction; erosion in the slope and runoff is getting worse.2. Slight erosion had a net increase of 237.32 km~2, with an increase of 6.52%, in 2005 and 2009; light erosion had a net increase of 735.54 km~2, with an increase of 20.22%, moderate erosion and intense erosion had a net loss of 918.47 km~2 and 57.7 km~2, reduced by 25% and 1.58%, and the good news is that extremely intense erosion disappeared in 2009. All in all, the overall intensity of soil erosion tends to be better in the 16 years from 1993 to 2009 in Anding District in Dingxi city.3. In 16 years from 1993 to 2009, in terms of land use types, forest and grassland have a huge increase from 494.22 km~2 in 1993 to 1295.87 km~2, while the land with the vegetation coverage between 45% and 60% increased to 1503.61 km~2 from 453.75 km~2 in 1993, the land with the vegetation coverage between 60% and 75% increased to 1503.61 km~2 from 453.75 km~2 in 1993, which is due to the long-term mechanism for returning farmland to forest project since 2000.Finally, the results have practical significance since they can directly provide a reliable basis for to management and rational use of land in Anding District in Dingxi City. |
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