Evaluating urban-rural gradients and urban forms in metropolitan areas: a local climate zone approach with future spatial simulation

Traditional analyses of urban-rural gradients and urban forms often encounter uncertainties related to subjective urban center point selection, oversight of the three-dimensional city form, and limitations in studies involving polycentric regions and strip-shaped urban areas. This study addresses these challenges by leveraging local climate zones (LCZs) to establish urban-rural gradients and simulate urban form in the Guangdong-Hong KongMacao Greater Bay Area (GBA). Through a comprehensive comparison between LCZs and concentric ring analysis, we computed urban-rural gradients and identified urban forms, assessing their capabilities in characterizing changes in urban features. Future changes in urban-rural gradients and urban forms were predicted based on the spatial simulation of the LCZs. The results indicate that urban-rural gradients using LCZs excel in urban form analysis, outperforming concentric ring analysis. In 2020, the GBA exhibited a decentralized-sprawl form in the concentric ring analysis, in contrast to the central-sprawl form identified through the LCZs analysis. The core areas of cities predominantly assumed a central form in the LCZs analysis, whereas the concentric ring analysis portrayed decentralized forms in city cores. The GBA, Macao, Zhongshan, and Zhaoqing anticipate significant urban form changes from 2020 to 2100 under different shared socioeconomic pathways simulated by LCZs. Most cities exhibited a noteworthy increase in urban compacity, with Shenzhen surpassing Hong Kong as the most compact city. Additionally, this study introduces a universal urban-rural gradient partitioning scheme, offering a fresh perspective for urban morphology studies and urban planning management.