| Vegetation is one of the most important influence factors of soil erosion. In soil erosion research, the influence of vegetation on soil is usually expressed by vegetation coverage. Commonly used projection vegetation coverage has some limitations in the characterization of vegetation’s soil and water conservation functions. Structural vegetation coverage is designed to overcome this limitation, to comprehensively reflect the influence of community coverage on soil erosion, but most relevant research is still on theoretical stage. Applying structural vegetation coverage as an index of vegetation factor to quantitative soil erosion evaluation practice and validating its rationality and applicability is of great significance, will, help correctly understand the relationship between vegetation and soil erosion, improve quantitative soil erosion research method system, and scientifically guide regional soil erosion control and ecological environment construction.The research is carried out in the Yan River Basin, which is located in northern Shaanxi Province and belongs to the Loess plateau. Using the daily rainfall data in 2013, Landsat 8 OLI images, SRTM DEM, land use map, soil K value map, transfer station measured runoff/sediment data as data sources, the research is completed mainly through RS and GIS spatial analysis technology. Based on structural vegetation coverage remote sensing model and dimidiate pixel model respectively, structural vegetation coverage and NDVI vegetation coverage in the study area were extracted and compared in various respects. With the two vegetation coverage as the index of vegetation factor respectively, USLE-based quantitative soil erosion evaluation and validation were conducted to analyze the rationality of structural vegetation coverage, and the applicability of structural vegetation coverage remote sensing model in the quantitative evaluation of regional soil erosion. The following main results have been achieved:1. The comparative analyses of the structural vegetation coverage and NDVI vegetation coverage.Extract and compare the NDVI vegetation coverage and structural vegetation coverage of Yan River Basin in 2013. The results show that in terms of statistical parameters, structural vegetation coverage has smaller range, mean and standard deviation than NDVI vegetation coverage. The space distributions of structural vegetation coverage and NDVI vegetation coverage are similar. According to coverage classification statistical analyses, the vegetation situation under NDVI vegetation coverage is far better than that of structural vegetation coverage. The NDVI vegetation coverage and structural vegetation coverage of vegetation with different structure types are quite different. Structural vegetation coverage can overcome the inherent defects of NDVI vegetation coverage and can more accurately reflect the actual vegetation situation.2. The quantitative evaluation of soil erosion based on USLE.Using structural vegetation coverage and NDVI vegetation coverage as an index of vegetation factor to get the cover and management factor required by USLE. Run USLE on GIS platform to produce regional soil erosion intensity map; Combine the map with the soil erosion classification standard of the Ministry of Water Resources (SL 190-2007) to complete soil erosion intensity classification. Results show that under the NDVI vegetation coverage, soil erosion modulus ranges from 9.75 to 110535.26 t · km-2 · a-1, averaging 12867.12 t·km-2·a-1. And the soil erosion intensity is mainly at mild and moderate levels. Based on structural vegetation coverage, soil erosion modulus is between 25.27 and 165801.39 t·km-2·a-1, with 16176.88t·km-2·a-1 on average. And the soil erosion intensity is mainly at ultra-strong and severe levels.3. Applicability analysis of the structural vegetation coverage remote sensing model.Combining the observed watershed sediment discharge data of transfer stations to verify the soil erosion evaluation results calculated with structural vegetation coverage and NDVI vegetation coverage as indexes of vegetation factor respectively and analyze the applicability of structural vegetation coverage remote sensing model in quantitative regional soil erosion evaluation. Results show that with the NDVI vegetation coverage, the erosion/sediment discharge has a value of 2.96, while with the structural vegetation coverage, the erosion/sediment discharge has a value of 3.74, which is more close to the average value (3.87) during many years. This suggests that structural vegetation coverage can more accurately reflect the actual situation of regional soil erosion, and is more suitable for quantitative evaluation of regional soil erosion. |
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