Evolutionary characteristics and influencing mechanisms of green development efficiency in Chinese urban agglomerations: Analysis of the Yangtze River Delta urban agglomeration.

Urban agglomerations are central to global economic growth and the shift towards green development, particularly in developing countries. This study examines regional comparisons and variations in green development mechanisms within urban agglomerations to better understand their spatiotemporal patterns. An input-output indicator system was developed, accounting for social benefits and carbon emissions. Using the Yangtze River Delta urban agglomeration (YRDUA) as a case, this study measured green development efficiency (GDE) from 2003 to 2022 with the SBM-Undesirable model. It also employed the coefficient of variation (CV) method and Markov chain model to analyze the spatiotemporal variability and dynamic transformation law of GDE. Additionally, a panel quantile regression model was used to identify the dynamic response of key controlling factors, based on the GDE stages of each city. The findings reveal: (1) Cities in the central YRDUA area have higher GDE levels compared to those in non-central areas, with increasing disparity over time. (2) The green development level of a city influences its neighbors, enhancing or degrading their GDE stability and type. (3) Economic growth, foreign direct investment, industrial structure, and technological innovation significantly impact YRDUA's GDE. (4) In cities with low green development, economic growth strongly promotes GDE, while government regulation most restricts it. In medium-level cities, industrial structure advancements have the largest promotional effect, whereas technological innovation is the most limiting factor. In high-level cities, foreign investment intensity is the main inhibitor, while government regulation supports GDE. Marketization and environmental regulation effects on GDE remain consistent across different city levels. These findings provide targeted guidance for the green transition of urban agglomerations in China and other developing nations.