Tracing trajectories and co-evolution of metropolitan urbanization in the United States, Europe, and China.

ABSTRACT

Metropolization has emerged as a prominent feature of 21st-century urbanization. To gain a comprehensive understanding of global urbanization patterns and pathways, as well as to interpret their consequences and implications, we aimed to provide a comparative characterization on urban transformation in metropolitan areas of developed and developing countries. Here, we quantified and compared the urban growth rates, growth modes, urban landscape metrics, and the co-evolution of urban land and population in 21 representative metropolitan areas across the United States, Europe, and China from 1985 to 2020, using remotely sensed impervious-surface dynamic dataset and patch-based analyses. The results showed that each metropolitan area has experienced substantial urban expansion with different scales and growth rates. Developing China possessed a relatively lower urbanization level but urbanized faster compared to the developed counterparts. Spatially, with infilling expansion increasing and even dominating, American and European metropolitan areas developed into more compact central urban cores, demonstrating the coalesced trajectories. Chinese metropolitan areas showed point-axis urban development mainly via edge-expansion in concentric rings. Furthermore, the horizontal co-evolution of urban area and population generally showed stable economies of scale in the United States and Europe whereas transitioned from diseconomy to economy of scale in China, evidencing that the century-long urbanization journey traversed by developed countries can be completed by emerging-developing ones within several decades. Temporally, the urban expansion greatly outpaced population growth in all metropolitan areas except London, signifying that urban land use efficiency is still a grand challenge in the Metropolitan Century. Effective metropolitan governance should be tailored to spatial configuration for efficient urban land use and intercity coordinated development towards a sustainable urban future, particularly for developing countries with emerging metropolization.