Evaluating Urban Green Development Capacity in Coastal Cities of Eastern China: An Entropy Weight–TOPSIS Approach

Urban sustainability is increasingly challenged in rapidly transforming coastal regions. This study operationalizes urban green development capacity as a measurable proxy for urban sustainability and constructs a multidimensional assessment framework integrating economic development, technological innovation, green transformation performance, and green coordination capacity. Using the entropy weight–TOPSIS method, we conduct a longitudinal analysis of Qingdao (2014–2023) and a cross-sectional comparison of 24 coastal cities in eastern China in 2023. Qingdao’s composite score increased steadily from 0.25 in 2014 to 0.81 in 2023, with post-2020 growth accelerating markedly following structural and policy adjustments. In contrast, inter-city disparities remain substantial: the leading cities exhibit sustainability capacity levels nearly twofold higher than those at the lower end of the distribution. Cities with stronger technological innovation intensity and institutional coordination consistently outperform others, highlighting the importance of governance–technology coupling. These results suggest that urban sustainability is associated with a coupled interaction pattern among capital, technology, performance, and institutional coordination rather than linear economic expansion. The study provides a quantitative tool for measuring and benchmarking urban sustainability capacity and offers empirical support for differentiated sustainability transition pathways in coastal and transition-economy cities.