The transitional characteristics of soil erosion in the earth-rocky mountain area-loess area of northern China under extreme rainstorm in 2023

Background In recent years, extreme rainstorm has occurred frequently in northern China, causing serious soil and water erosion. In 2023, extreme heavy rainfall events occurred in northern China under the influence of Typhoon Du Suri. To explore the regional differences and causes of soil erosion caused by large-scale extreme rainstorm, this article selected Jingxing county in Hebei, Lingqiu county in Shanxi, and Binzhou city in Shaanxi as research objects, and finally proposed response strategies for different regions.

Methods This article adopted a combination of on-site manual measurement and drone aerial photography. Typical small watersheds were selected in the survey area. After orthophoto by UAV, the location and degree of soil erosion in small watersheds were preliminarily analyzed according to the images. Finally, different land use types such as sloping farmland, terraces and roads in the small watershed were selected, and the field measurement was carried out by sampling method. The corresponding erosion modulus using different methods based on different types of land use erosion was calculated.

Results 1) Under extreme rainstorm, soil erosion was mainly concentrated in slope farmland, terraces, roads and other land use types, while forest and grassland erosion was lighter. From the earth-rock mountain area to the loess area, the soil erosion intensity was increasing. 2) The erosion of slope farmland was the most serious, mainly gully erosion. The erosion modulus of soil-rock mountain area, transition area and loess area were 16 613, 39 963 and 65 232 t/km², respectively. 3) Terraced fields were primarily affected by gravitational erosion on field ridges. The damage rates of field ridges in the three regions were 11.92%, 18.54%, and 37.64%, respectively. The erosion modulus was 22 939, 29 314, and 41 463 t/km², respectively. The erosion degree of soil ridge terrace was significantly higher than that of stone ridge terrace. 4) Road erosion was primarily characterized by collapse of side slopes and surface gully erosion. The erosion modulus from side slope collapse on roads in the three regions were 13 004, 25 283, and 48 859 t/km², respectively. The erosion modulus from surface gully erosion on roads were 5 948, 17 134, and 43 498 t/km², respectively. Erosion on earth roads was more serious, and stone roads were relatively light.

Conclusions The concentrated flow generated by rainstorm is the main driving factor of soil erosion. The varying degrees of erosion in different regions are mainly due to differences in local soil and water conservation measures and geographical environment. It is necessary to strengthen the construction of interception and drainage measures. In addition, it is necessary to continuously strengthen the construction of high-standard terraces in earth-rocky mountainous areas, consider increasing the proportion of stone ridge terraces in transitional areas, and strengthen agronomic management in loess areas to avoid surface exposure. The research results can provide a scientific basis for the precise implementation of soil and water loss zoning.