The evolution of ecological security and its drivers in the Yellow River Basin.

Ecological security is the state achieved once an ecosystem maintains its stability under external stress. The Yellow River Basin (YRB) is the largest river basin in northwest and north China and an important area for grain and energy production. The assessment and attribution of ecological security in the YRB are important for protecting the natural environment and ensuring sustainable development. Here, the ecological security of the YRB was assessed by the ecological security index (ESI), a comprehensive index based on the oxygen cycle, and its drivers were attributed to climate change, human activities, vegetation, and soil factors. The spatial pattern of ecological security in the YRB showed high heterogeneity. Ecological insecurity occurred mainly in the middle reaches and regions where the major stream of the Yellow River passes through. The ESI decreased at a rate of - 0.82/year since 2000, which indicated the natural environment continued to be improved in the YRB. Climate change dominated the evolution of ecological security in the upper reaches. The level of ecological security has been improved in the middle reaches after a series of ecological restoration projects conducted. With higher intensity of industrial activity, human activities played a more critical role in ecological security in the lower reaches. Our results suggested that government and local people need to adopt different strategies and actions based on the dominant drivers in the upper, middle, and lower reaches to ensure protection of the natural environment and achieve sustainable development targets.