A comparative analysis of urban impervious surface and green space and their dynamics among 318 different size cities in China in the past 25 years

Urban impervious surface (UIS) and urban green space (UGS) fractions in a city are essential indicators in supporting urban planning and management. However, little is known about the dynamics of urban expansion and the resultant UIS/UGS fraction in different size cities in China over time. We comparatively analyzed the urban expansion, UIS/UGS, and their dynamics among 318 different size cities during 1990–2015 derived from the China Land Use/cover Datasets (CLUDs) and the UIS/UGS datasets. The results indicate that the urban expansion area for the 318 cities increased by 2.32 × 104 km2 during 1990–2015, with an average growth percentage of 4.37%. Megacities experienced dramatic expansion between 1990 and 2000, and the urban expansion of large and medium cities increased rapidly in the following decade. During 2010–2015, the urban expansion of small cities notably increased. Meanwhile, the proportion of the UIS fraction in newly expanded urban land continuously decreased during 1990–2015. Compared to the other three size cities, the proportion of the UGS fraction in megacities was the highest (24.55%) in 1990 and then increased (27.99–31.97%) in newly expanded urban land during 1990–2015 due to ecological construction. Thus, more attention should be paid to the dynamics of urban expansion, especially in small cities. The proportions of UGS in large, medium, and small cities are relatively low, and urban environment needs to be improved for greenness and livability in the future.