Coupling coordination degree analysis and spatiotemporal heterogeneity between water ecosystem service value and water system in Yellow River Basin cities

Accelerated urbanization has caused encroachment on urban water ecological land in China's Yellow River basin, resulting in a strong disturbance of water ecosystem service functions and increasingly serious water ecological environmental problems. In this study, two entities-water ecosystem service value (WESV) and the urban water system-are identified, to investigate the interactions between WESV and the urban water systems and their subsystems in six Yellow River basin cities (Lanzhou, Yinchuan, Hohhot, Xi'an, Zhengzhou, and Jinan) from 2005 to 2020. First, the integrated level of the WESV and the water system in each city is calculated using the modified and developed method of equivalence factor per unit area and the entropy method, respectively. Then, the coupling coordination relationship and interactions between WESV and the water system in each city are revealed by using the coupling coordination degree model (CCDM) and the Geographically and Temporally Weighted Regression (GTWR). The results show that: 1) The level of both WESV and the water system in each city basically shows an increasing trend, the hydrological regulation function dominates the water ecosystem service functions, and the comprehensive evaluation level of the water environment is generally higher than that of the other urban water system's subsystems. 2) The degree of coupling coordination between WESV and the water system in each city gradually rose from extreme incoordination to basically coordination, and the coupling coordination degree (CCD) between WESV and the water environment and the water resources also shows an obvious upward trend, but the CCD between WESV and water safety is developing more slowly. 3) The area where the WESV and the water system have greater positive impacts are primarily focused in Lanzhou and Xi'an, while the negative impacts are mainly located in Yinchuan and Zhengzhou. In summary, in the planning and decision-making of cities in the Yellow River basin or other basin cities, it is critical to promote the protection of water ecology and high-quality development in cities by clearly understanding the interaction between water ecosystem services and the water system, and coordinating and balancing development between the two systems.