Exploring the temporal and spatial effects of city size on regional economic integration: Evidence from the Yangtze River Economic Belt in China

The continuous expansion of cities has led to prominent threats of urban housing shortage, inefficient land use, and environmental degradation. Determining an appropriate city size to promote REI is a fundamental problem in China's new-type urbanization period. This study investigated the impact of city size on REI from the spatio-temporal perspective, and performed an empirical investigation of such effects through spatial models, using panel data for 2004-2019 for 108 cities in the Yangtze River Economic Belt (YREB). The results demonstrate that city size has an inverted U-shaped effect on REI, and the effects vary across urban agglomerations in the YREB. Moreover, we calculated their growth potential from the REI perspective based on 2019 data. This study examined 108 cities and found that 30 of them had exceeded their optimal size for efficiency during the REI process, highlighting the need for spatial territorial governance, management, and planning. Of the remaining cities, 68 were near their REI efficiency-maximizing size, with no more than 20% growth potential. Only 6 cities had the potential to expand between 20% and 50%, while 4 cities had the capacity to grow by more than 50%. Therefore, governments must develop tailored land use and urban management policies for each city to enhance their REI.