Quantifying thresholds of key drivers for ecosystem health in large-scale river basins: A case study of the upper and...

Under the dual pressures of global climate change and anthropogenic activities, identifying key thresholds for ecosystem health is essential for biodiversity conservation, climate change mitigation, and regional sustainable development. Utilizing the vitality-organization-resilience-service model, this study quantifies the spatiotemporal evolution of ecosystem health in the upper and middle reaches of the Yellow River from 2000 to 2020. Extreme precipitation indices, integrated with partial least squares structural equation modeling, were employed to elucidate the mechanisms by which extreme rainfall impacts ecosystem health. The results indicate that:(1) Both ecosystem vitality and ecosystem organization increased, reflecting enhanced ecosystem stability and connectivity, with significant vegetation recovery in forest and grassland regions. (2) Ecosystem health significantly improved in 69.48 % of the regions. The improvement of ecosystem health in the midstream is primarily attributed to the extensive restoration of forest and grassland. Ecological restoration did not substantially change the ecological vulnerability of the northern desert areas, and restoration should be prioritized in the future. (3) As a primary driver of ecosystem health, moderate increases in vegetation coverage can enhance ecosystem health; the threshold values for nighttime light intensity, relative humidity, precipitation, and land use intensity are 0.6, 68.61 %, 789.92 mm, and 2.34, respectively. (4) Extreme precipitation indirectly affects ecosystem health by influencing vegetation, with a combined contribution rate of 26.10 %. The long-term impact of single extreme precipitation events is limited, and cumulative precipitation events have a greater effect on ecosystem stability. This study determines the threshold of environmental and anthropogenic factors on ecosystem health and clarifies the indirect impact of extreme precipitation on ecosystem health through vegetation, thereby providing a scientific basis for the sustainable management of large-scale vulnerable river systems.