Effect of land use change on soil erosion by water in the Niyang River Basin of Tibet during 1990–2020

Abstract In alpine gorge regions, human activities are concentrated on limited river terraces, yet whether the resulting land use changes exacerbate soil erosion at the basin scale remains unclear. This study aimed to quantify the spatiotemporal dynamics of land use and soil erosion by water in the Niyang River Basin, a representative alpine gorge in Tibet, from 1990 to 2020, and to identify the dominant controlling factors. Land use changes were analyzed using Landsat imagery, soil erosion was estimated using the Revised Universal Soil Loss Equation (RUSLE), and the relative importance of elevation, slope, aspect, soil sand content, temperature, precipitation, vegetation coverage, and land use type was quantified using an optimal parameters-based geographical detector model. The results showed that cropland and construction land expanded 2.4-fold and 6.1-fold, respectively, while forest and water areas declined. Land use exhibited clear vertical zonation: cropland and construction land were concentrated below 4,100 m, forests and grasslands dominated the mid-elevation belt, and unused land prevailed above 4,853 m. Tolerable and slight erosion covered over 82% of the basin, whereas severe, very severe, and destructive erosion classes occupied less than 6% of the area but contributed over 27% of total soil loss. The total soil loss by water decreased from 27.46 Mt in 1990 to 21.98 Mt in 2020, with over 85% of the basin maintaining a stable erosion class. Grasslands, forests, and unused land generated 99% of total soil loss. Geographical detector analysis revealed that soil sand content and vegetation coverage were the dominant controlling factors, with vegetation coverage becoming the primary factor by 2020, whereas land use type consistently ranked lowest in explanatory power. All factor interactions exhibited synergistic effects, with soil sand content × aspect showing the highest explanatory power. These findings demonstrate that although conversion of natural land to cropland caused localized erosion enhancement, human activities concentrated on limited river terraces did not lead to a basin-wide increase in soil erosion. The overall reduction in soil loss is attributed to the dominance of natural vegetation cover and the effectiveness of ecological restoration policies. We recommend prioritizing the protection of grasslands and forests, implementing targeted erosion control in hotspot townships, strictly regulating cropland expansion onto steep slopes, and promoting scientific farming practices. The results provide a scientific basis for balancing socio-economic development with ecological security in alpine gorge regions of the Qinghai-Tibet Plateau.