Soil Erosion Characteristics at Small Watersheds Along Milin Region in the Yarlung Tsangpo River

Objective The Yarlung Tsangpo River, China’s longest highland river, possesses substantial water resources. Despite its significance, the river faces critical environmental challenges, including severe soil erosion, frequent landslides, and mudslides. These natural disturbances contribute to sediment siltation and riverbed blockages, undermining the river’s ecological integrity and hindering sustainable hydropower development in the basin. This study plays a critical role in analyzing soil erosion dynamics, which are essential for effective water resource management and strategic hydropower planning by emphasizing the urgency of addressing these environmental issues.Methods This research utilized the RUSLE model to quantify soil erosion processes in 12 representative sub-watersheds of the Yarlung Tsangpo River’s Milin section, specifically focusing on the changes in erosion patterns before and after a significant earthquake. It employed a geo-detector approach to identify the primary drivers of soil erosion within these sub-watersheds. Through a comprehensive analysis of multiple interacting factors, the research clarified the complex mechanisms driving soil erosion and determined high-risk areas, guiding targeted interventions to strengthen the ecological resilience of the region against ongoing and future environmental challenges.Results and Discussions The results showed that the <italic>LS</italic> factor distribution indicates the study area’s high altitude and significant topographic relief <italic>C</italic> factor values between 0.35 and 0.45 revealed poorer vegetation cover on high-altitude ridges and better cover at lower altitudes. <italic>K</italic> values ranged from 0 to 0.102 5, indicating lower soil erodibility at lower altitudes and higher erodibility at ridges. <italic>P</italic> values decreased from 2001 to 2016 and then increased after 2016. Rainfall erosivity showed a general downward trend, with fluctuations from 2008 to 2010. It was lower in high-altitude areas and stronger at lower elevations. From 2001 to 2020, the study area experienced an average soil erosion rate of 3 464.18 t·km^–2·a^–1, with over 60% of the area experiencing slight to mild erosion. The average soil erosion modulus in 2009 was the lowest, at 1 985.24 t·km^–2·a^–1, while the highest soil erosion occurred in 2008, with an average soil erosion modulus of 4 715.40 t·km^–2·a^–1. Among them, the average annual erosion in Dokongpu, Ruxiapuqu, and Dannianggou exceeded 300 000 t, which was related to the characteristics of a larger watershed area and higher elevation. The year 2016, which had the best vegetation cover, exhibited minimum erosion. The ecological environment was more stable, while the multi-year average erosion in the Menzupu, Benga, and Eadong (Qulu) sub-watersheds did not exceed 100 000 t. Before the earthquake, the explanatory power of factors influencing soil erosion ranked as follows: NDVI, soil condition, elevation, land use, temperature, rainfall, and slope. Post-earthquake, temperature’s explanatory power for soil erosion surpassed that of land use, while the ranking of the other factors remained the same. Vegetation cover was the main driving factor and its interaction with topography and climate predominantly controlled soil erosion. The interaction between slope and other factors enhanced erosion nonlinearly, increasing the <italic>q</italic>-value by 1.9 to 4.7 times. Earthquakes significantly impacted sediment transport and geomorphological evolution in the Yarlung Tsangpo River Basin. They caused ridge and slope fractures, reduced soil erosion resistance, and triggered landslides in high-elevation areas, destroying vegetation and generating many bare surfaces and loose material sources. The erosion modulus generally exhibited a fluctuating decreasing trend from 2001 to 2016. However, after the earthquake in 2017, the erosion modulus increased annually, with a tendency for strongly and very strongly eroded areas to transform into intensely eroded areas. Before the earthquake, highly erosive areas were primarily distributed at ridges with higher elevations. However, after the earthquake, erosion increased at the ridges and in the low-elevation areas, which showed an increasing trend. The pre-earthquake multi-year average soil erosion modulus was 3 415.77 t·km^–2·a^–1, and the average <italic>R</italic> factor was 878.22 (MJ·mm)/(hm²·h·a). In comparison, the post-earthquake multi-year average soil erosion modulus was 3 657.81 t·km^–2·a^–1 with an average <italic>R</italic> factor value of 855.33 (MJ·mm)/(hm²·h·a). Despite reduced rainfall erosivity post-earthquake, erosion volumes increased, indicating that the earthquake lowered the threshold for rainfall-triggered erosion in the watershed. Therefore, before the earthquake, the watershed’s soil erosion pattern was characterized by the interaction between climatic conditions and vegetation cover, resulting in an overall decreasing trend in soil erosion. In contrast, after the earthquake, rainfall erosion thresholds decreased, temperature influence increased, and the watershed became more sensitive to climate change. Areas with elevations of 3 875 to 5 138 m, annual rainfall of 609 to 670 mm, temperatures ranging from 2.08 to 6.11 ℃, land-use types including shrubs, grasslands, and bare ground, slopes greater than 17.8°, and NDVI values less than 0.41 had a higher risk of soil erosion. After the earthquake, the degree of soil erosion in each risk area increased to varying extents. Among them, the soil erosion modulus of bare land increased by 56.88 t·km^–2·a^–1, while the soil erosion modulus in areas with NDVI values ranging from 0.05 to 0.14 reached 103.46 t·km^–2·a^–1.Conclusions The research results significantly enhance our understanding of the dynamic soil erosion characteristics within the Yarlung Tsangpo River Basin, highlighting how vegetation cover, topography, and climatic conditions interact to influence erosion processes. These insights clarify the complex environmental challenges facing the region and provide a solid scientific basis for the strategic planning and optimization of hydropower development projects. In addition, the findings provide essential data to inform and refine soil and water conservation policies, reduce erosion risks, and enhance the ecological stability of this critical watershed. The research contributes to sustainable resource management and the protection of vital habitats in the basin by addressing these key aspects.