Gradients and variations of green plot ratio in urban built-up areas: evidence from 110 Chinese cities in the Yangtze River economic belt

Abstract

Green plot ratio (GPR) is an ecological measure for urban greenspace, and an appropriate GPR is crucial in providing ecosystem services for urban residents, but the characteristics of GPR among different cities are still not clear, especially in built-up areas. Taking 110 Chinese cities in the Yangtze River Economic Belt as a case, this study quantitatively analyzed the index variations and spatial gradients of GPR in different urban built-up areas. First, from the river-basin level down to the provinces/municipalities and then to prefecture-level cities, the GPR results reveal significant heterogeneity across hierarchical spatial gradients. The middle reaches of the Yangtze River Economic Belt show the highest average greenspace and regional GPR (3.86 and 1.16). Specifically, cities in Hubei Province exhibit notable advantages in waterfront GPR (3.79), while Chongqing leads in greenspace and mountain-hill GPR (4.63 and 5.38). Second, GPR varies significantly across cities with different natural environments and city scales. Mountain-hill dominant cities exhibit the highest greenspace GPR with average values of 3.98, whereas plain dominant cities show the lowest GPR due to intensive urban construction. City scale corresponds to GPR patterns: large cities achieve the highest regional and greenspace GPR (1.27 and 3.83) with strong economic and infrastructural support, medium cities excel in waterfront and mountain-hill GPR (3.68 and 5.05), and small cities lag behind in all GPR indicators. This study develops evidence-based GPR references from spatial regulation and setting thresholds for eco-city development policy, and proposes setting differentiated goals based on individual cities' natural and scale-related attributes.