Evaluation and obstacle factors of high-quality development in coastal cities along the Yangtze River

In order to achieve marine environmental protection and sustainable development in the coastal regions along the Yangtze River, the Chinese government has formulated the "Implementation Plan for the Development of the Yangtze River Economic Belt (YREB)". High-quality urban development (HQUD) aims to achieve economic, social, and environmental benefits, making it an extension and reinforcement of the concept of sustainable development. This study employs this plan as a point of reference to construct an indicator framework for appraising HQUD. The system is designed based on a sustainability perspective, incorporating four dimensions, namely environment, circulation, economy, and society. Based on data collected from 105 cities in the YREB between 2003 and 2020, this study applies various methods including kernel density estimation, Dagum Gini coefficient, Markov chain analysis, Moran's I index, spatial beta convergence, and barrier models to examine the spatiotemporal evolution dynamics associated with HQUD trends in the region. The findings indicate that the overall level of HQUD experiences some fluctuations, but exhibits a net upward trend. However, cities belonging to different quality levels of development typically remain in their respective levels, with few jumping to higher levels. Next, the overall difference in HQUD originates from inter-regional differences and exhibits positive spatial aggregation characteristics. Further, the region's HQUD exhibits spatial convergence. Finally, the low level of social development remains an important issue that should be resolved urgently. Overall, this study reveals the current state of the Yangtze River coastal regions, offering theoretical and practical foundations for marine environmental protection and government policy formulation.