Evaluation and spatial distribution characteristics of freeze-thaw erosion intensity in the Yalu Tsangpo River basin on the basis of geographic information system

Freeze-thaw erosion is one of the main ways of soil erosion in three major erosion types, which are related to the development of regional economy and the protection of ecological environment. Therefore, its research is particularly important. This paper uses the Yalu Tsangpo River basin as the research area. The range of the freeze-thaw erosion area in the Yalu Tsangpo River basin was defined by using Shuttle Radar Topography Mission-Digital Elevation Model (STRM-DEM) data. Six factors, namely, annual temperature difference, annual precipitation, slope, aspect, vegetation coverage, and elevation, were selected as the evaluation indexes of the intensity of freeze-thaw erosion. Analytic hierarchy process (AHP) was used to determine the weight of each factor. A comprehensive evaluation index model was employed to obtain the range of freeze-thaw erosion intensity. The natural breaks method in ArcGIS was applied to grade the result. The classification chart of the freeze-thaw erosion intensity of the Yalu Tsangpo River basin was drawn to show the distribution of freeze-thaw erosion. Results showed that (1) the total area of freeze-thaw erosion in the Yalu Tsangpo River basin is 229,231.80 km(2), which accounts for 93.5% of the total area of the Yalu Tsangpo River basin, with mild erosion and moderate erosion. (2) The distribution of freeze-thaw erosion intensity in spatial pattern is obvious; from west to east, the intensity of freeze-thaw erosion increases gradually. Severe erosion is mainly concentrated in the northeast and northern regions of the Yalu Tsangpo River basin. (3) The areas of freeze-thaw erosion are mainly distributed in the temperature zone with the annual temperature range of >= 40 degrees C, accounting for 86.4% of the total freeze-thaw erosion area. The freeze-thaw erosion area is mainly distributed in the slope >= 15 degrees slope zone, which accounts for 62% of the total freeze-thaw erosion area, and has a severe effect on moderate erosion and severe erosion in this slope zone. Freeze-thaw erosion areas are mainly concentrated in vegetation belts with vegetation coverage less than 20%, accounting for 63.8% of the total freeze-thaw erosion area. With the increase in vegetation coverage, the proportion of freeze-thaw erosion area decreased. The freeze-thaw erosion area was mainly concentrated on the altitude zone of >= 4000 m, which accounted for 84.3% of the total freeze-thaw erosion area. Thus, the freeze-thaw erosion area increased with altitude.