Magnitude of soil erosion in small catchments with different land use patterns under an extreme rainstorm event over the Northern Loess Plateau, China

Abstract

Characteristics of soil erosion under extreme rainfall conditions are indicators of the ecological restoration measures as well as the rationality of land use patterns in the region. To this end, 12 dam-controlled catchments were selected for investigation after an extreme rainstorm event in the northern Shaanxi Province on 25–26 July 2017 (known as the “7.26” rainstorm). Soil erosion intensities in the 12 catchments were obtained by excavations of sedimentation profiles and sedimentation area measurements. Digital orthophoto maps and digital terrain models by unmanned aerial vehicle were generated to characterise land use types and areas, slope gradients, and the distance from the land to the boundary of dam-land along the flow accumulation path. Stepwise regression analysis was used to determine the main factors affecting catchment erosion intensity. Results showed that the average sedimentation thickness and overall soil erosion intensity across the 12 catchments ranged from 0.16 to 1.67 m and 10295–49227 t km−2, respectively. Soil erosion caused by the extreme rainstorm was 10–50 times of the soil loss tolerance on the Loess Plateau (1000 t km−2 year−1). Stepwise regression analysis revealed that the more similar the shape of a catchment to a circle, the closer the distance between the slope-cropland and dam-land, the larger the erosion modulus within the catchment. Furthermore, the presence of a cement road along the valley shoulder greatly reduced the modulus of soil erosion. These findings indicate that the existing ecological conditions in the dam-controlled catchments were not able to effectively resist erosion under the extreme rainfall conditions of this event. Thus, optimising the distribution of land use types within catchments should be a focus for soil erosion control.