Grading Evaluation of Multi Factor Soil Freeze-thaw Erosion Intensity Based on GIS——A case study of the upper reache of the Yangtze River

Freeze-thaw erosion is the third largest type of soil erosion after wind erosion and water erosion. Taking the upper reaches of the Yangtze River as an example, we use annual temperature difference, maximum frozen depth, thickness of active layers, elevation, annual precipitation, slope, the content of fine grained soil, the vegetation coverage, slope to the nine freeze-thaw erosion factors as evaluation index, and weighted sum of standardized values method was adopted to realize the freeze-thaw erosion intensity relative to classification. The spatial distribution characteristics of freeze-thaw erosion in this area are also discussed in order to provide reference for soil and water conservation research and ecological environment construction in this area. The analysis results show that the total area of freeze-thaw erosion in the study area is about 55.8×10~4 km~2, which is mainly intense erosion and extremely intense erosion, accounting for 30% and 25% of the total area of freeze-thaw erosion in the study area, and mainly distributed in the areas of Wudaoliang-Tuotuo River east and Kangding-Jiulong-Shangri-La west. With the warming of the Qinghai-Tibet Plateau, the degradation of permafrost, and the increase of freeze-thaw disasters, freeze-thaw erosion may show an increasing trend in the future, which brings new problems to the regional ecological environment restoration and engineering construction.