Simulation of carbon sink-welfare coupling and policy regulation in the Yellow River Basin under blue-green-grey space synergy

The coordinated governance of carbon sinks and welfare in the Yellow River Basin represents a crucial practice for China in implementing the "dual carbon" strategy, which can offer a reference for the sustainable development of major river basins globally. Based on socio-ecological system theory and multi-source data including land use data and socioeconomic statistics from 2000 to 2020, we constructed a dynamic analytical framework that integrating PLUS land use simulation, ARIMA time series forecasting, and a coupled coordination model. We further revealed the spatiotemporal variations of the carbon sink-well-being coupling under the transformation of blue, green, and grey spaces in the Yellow River Basin from 2000 to 2020, and then simulated and evaluated the variations of the carbon sink-well-being coupling relationship and the effects of policy interventions by 2030. The results showed that land use change in the Yellow River Basin followed a "four increases, two decreases" pattern between 2000 and 2020, with forest, grassland, water body, and construction land continuing to expand and cropland and bare land were contracted. Overall, the pattern exhibited a spatial differentiation characterized by "preserving green in the upstream and expanding grey in the downstream". Carbon sink levels and resident well-being indices generally continued to rise. The coordination of the carbon sink-well-being coupling gradually shifted from being dominated by disharmony toward a state of harmony, with the proportion of cities exhibiting disharmony decreasing from 61.7% in 2000 to 18.9% in 2020. However, the proportion of cities with lagging carbon sinks rose to 64.8%, indicating intensified regional divergence. By 2030, the expansion of construction land would continue, squeezing the ecological space of some downstream cities and slowing the growth trend of carbon sinks. The residents' well-being would continue to improve, whereas the coupling coordination (D) of upstream cities would mostly remain at a high-quality coordination stage (D>0.9). The downstream cities such as Zhengzhou and Jinan would remain trapped in an "high well-being-low carbon sink" imbalance (D≤0.9). Although policy interventions can improve coordination, over 60% of carbon sink-lagging cities would be unable to shift their development patterns even under mandatory interventions due to the dual constrains of structural rigidity and diminishing marginal effects. Considering this, we proposed three governance orientations: coordinated development type, welfare improvement-led type, and carbon sink improvement-led type, which would provide a scientific basis for the differentiated governance of territorial space within river basins.