Coupling Coordination and Obstacle Diagnosis of the Water Resource–Society Economy–Ecological Environment System in the Lower Yellow River Basin

Understanding the interactions between water resource utilization, socioeconomic development, and the ecological environment is fundamental to ensuring ecological security and promoting sustainable development in the lower Yellow River region. This study developed a composite system integrating water resources, socioeconomic development, and ecological environment for 27 cities in the lower Yellow River Basin. The indicator weights were determined using the combined Analytic Hierarchy Process (AHP) and entropy weight method. Subsequently, several models, including Technique for Order Preference by Similarity to Ideal Solution (TOPSIS), the coupling coordination degree (CCD) model, spatial autocorrelation, and obstacle degree analysis, were integrated to systematically evaluate the spatiotemporal evolution, coordination patterns, and key constraints of the composite system. The findings indicate that the development of the three subsystems surged with fluctuations, following the gradient pattern of ecological environment > socio-economic development > water resources. The water resource subsystem improved slowly and remained the main constraint. The CCD gradually shifted from barely and primarily coordinated stages to intermediate and well-coordinated stages. Spatially, Shandong outperformed Henan, eastern areas exceeded western areas, and core cities showed higher coordination levels than inland cities. Significant and increasing positive spatial autocorrelation indicated strengthened spatial agglomeration, with high–high clusters in eastern Shandong and low–low clusters in western and northwestern Henan. The per capita water resource indicator emerged as the dominant obstacle, while forest and grassland area, the Normalized Difference Vegetation Index (NDVI), agricultural water use, and the share of the tertiary industry also constituted major constraints.