Classification evaluation and spatial distribution characteristics of freeze-thaw erosion intensity in Heilongjiang Province of China

Freeze-thaw erosion has occurred mostly in the alpine areas of the Qinghai-Tibet Plateau and the high-latitude area of Northeast China. Among them, Heilongjiang Province can be primarily responsible to maintain the national ecological and food security in the northeast region at present. However, the freeze-thaw erosion has seriously threatened to the natural environment and black soil resources in recent years. This study aims to quantitatively reveal the spatial heterogeneity of freeze-thaw erosion intensity and its influencing factors in Heilongjiang Province. 10 evaluation indexes of freeze-thaw erosion intensity were selected to determine their weights. The lower limit of freeze-thaw erosion was obtained to construct the multiple regression model. Finally, the distribution range of freeze-thaw erosion was drawn in the study area. The weight and assignment were then substituted into the comprehensive evaluation index model. The natural breakpoint was used to classify for the distribution map of freeze-thaw erosion intensity. The results showed that: (1) The distribution range of freeze-thaw erosion was located between 121°E-135°E and 47°N-54°N, in the north isoline of average annual ground temperature of 3℃, and about 2 latitudes lower than the southern boundary of permafrost probability. The total area of freeze-thaw erosion was 1.917×10⁵ km², accounting for 40.53% of Heilongjiang Province. The intense and extremely erosion were accounted for 20.66% and 10.54% of the total area of freeze-thaw erosion, respectively. (2) There was the spatial heterogeneity in the distribution of freeze-thaw erosion in the study area. The area above moderate freeze-thaw erosion presented the distribution of three areas and one belt. Specifically, the three areas were Daxinganling, Xiaoxing 'anling and Zhangguangcailing forest area; The belt was a corridor of "three ridges and one plain" from northwest to southeast. (3) The intensity of freeze-thaw erosion showed the outstanding positive correlation and agglomeration in spatial distribution. Areas with similar erosion intensity were tended to cluster spatially. By contrast, the high and low erosion intensity exhibited the spatial differentiation, leading to the multiple areas with the high and low intensity of frozen-thawed erosion. In addition, the high-low (HL) concentration areas were widely distributed in Xiaoxing 'anling area, high values of which were surrounded by low ones. (4) Freeze-thaw erosion was depended mainly on many factors, where the vegetation coverage and soil water content were contributed greatly. The increasing vegetation coverage was reduced the intensity of freeze-thaw erosion, especially where the vegetation coverage was less than 20%. The area proportion of mild, moderate, and intense erosion decreased with the increase of vegetation coverage. The freeze-thaw erosion occurred mainly in the areas with the soil water content of 0.2-0.3 m³/m³, but rarely occurred in the areas with the soil water content of less than 0.2 m³/m³. Therefore, the proportion of moderate and intense erosion increased with the increase of soil water content. These findings can provide the technical reference to protect and manage the frozen-thawed erosion in the similar areas.