Uneven urban-region sprawl of China's megaregions and the spatial relevancy in a multi-scale approach

As a global phenomenon, megaregions are now and will continue to be the main form of urbanization, especially in developing countries including China. Although megaregions have been viewed as the most powerful formation to accelerate urbanization, the unprecedented regional growth and the uneven urban-region sprawl between different cities are emerging as critical problems. Despite many concerns about rapid regional growth from social and economic perspectives, not much is known about the multi-scale dynamic of urban-region sprawl in terms of land use. In this study, we examined the two most important megaregions of China, the BeijingTianjin-Hebei region (B-T-H) and the Yangtze River Delta region (Y-R-D), to understand their urban-region sprawl patterns and the relevancy of multiple spatial scales among different types of cities. The analysis included directly identifying the developed land from remotely sensed data collected between 1980 and 2010. The results showed that (1) at the regional scale, although both megaregions expanded rapidly during 1980-2010, the obvious difference existed in their regional sprawl patterns. The sprawling rate of Y-R-D was obviously higher than that of B-T-H, implying the megaregions implemented quite different development strategies. (2) At the city scale, both the dominant and non-dominant cities within the megaregions had distinct contributions to the regional sprawl of the mega cities. The greatest contribution from the dominant cities was the fast expansion of the main urban areas; the greatest contribution of the non-dominant cities was the fast rural sprawl. Overall, the varied spatial differences in the regional sprawl of China's megaregions highlight that sustainable regional development requires multi-scale joint development plan management, not only considering the synergy of cities with different sizes, but also the synergy between urban and rural areas.