Driving mechanism of urban expansion in the Bohai Rim urban agglomeration from the perspective of spatiotemporal dynamic analysis.

The urban agglomeration represents the predominant form of new urbanisation, yet the evolution of its internal spatial structure exhibits pronounced spatial and temporal heterogeneity. This study concentrates on the Bohai Rim urban agglomeration, one of three major urban agglomerations in China, which has received comparatively limited research attention but has also undergone substantial urbanisation. Therefore, we reassessed and explored the spatial-temporal evolution of the spatial structure of urban expansion using Exploratory Spatiotemporal Data Analysis (ESTDA), and summarized the driving mechanisms using Geographically and Temporally Weighted Regression (GTWR). Our study found that the urban land expansion intensity of Bohai Rim urban agglomeration presented the differences between megacities and large cities, coastal and inland cities and the regional disparities exhibited a gradual narrowing and balancing over time and space, with the high-expansion intensity zones undergoing alternation. The dynamics of the local spatial structure performed a clear positive correlation with the development level and a negative correlation with the exploitation time. The urban expansion intensity was influenced by various factors, including population, economic and other variables. Over time, the main drivers shifted from emphasis on economic quantity to quality, and from financial support to government policy. The objective of this study is to substantiate the impact of socio-economic factors on the spatio-temporal heterogeneity of urban expansion and to propose strategies for alleviating urban land pressure in the Bay Area urban agglomerations. This study enriches the research on the urban expansion mechanisms of different types of urban agglomerations and enhances a comprehensive understanding of the spatiotemporal heterogeneity of urban expansion within it. The findings can provide valuable theoretical support for urban planners in future urban development and construction and can also serve as exemplars for urbanisation in other urban agglomerations.