Objective The deepening analysis of the relationship between green space and population in cities within the Yangtze River Delta is important for promoting the new urbanization construction in the context of regional integration.
Methods This research introduces a scaling law model to analyze the spatial and temporal characteristics of the scaling factors of urban green space during the period from 2000 to 2020 by selecting 41 cities in the Yangtze River Delta as research units. The scaling law model is suitable for measuring the non-linear scaling relationship between urban elements and urban population size, which can be used to analyze the scaling factors of urban green space elements and urban population size in the same time section.
Results 1) In terms of the global characteristics of scaling factor, the scaling factor characteristics of urban green space in the Yangtze River Delta can reflect the stronger scale effect of each type of green space. The scaling factors of built-up area in the Yangtze River Delta are always in a sublinear pattern, and evolve in a temporal sequence of “decline – rise – decline”, indicating that the utilization efficiency of built-up area increases with city scale, reflecting the increasingly intensified utilization of built-up area. The sublinear pattern of urban green space elements is synchronized with that of built-up area, and the sharing degree of urban green space elements increases with city scale. The level of scaling factors of urban green space elements in the Yangtze River Delta is low compared with the national level, reflecting that the scale effect of urban green space in the Yangtze River Delta is stronger than the national level, which is mainly due to the gradual transformation of urban green space from incremental expansion to stock optimization that is expected to gradually improve the spatial efficiency of urban green space, and also due to the fact that the larger city scale is, the higher the degree of fine configuration of urban green space will be. 2) In the comparison of the scaling factors of urban green space elements, the descending order of “park green space area > urban green space area > park area” is shown: The scaling factor of park green space area is the highest, which basically realizes the universal supply for population demanding in the urban system, and the sharing degree in big cities has some room for improvement; the scaling factors of urban green space area and built-up area are basically the similarity; the evolution of the scaling factors of urban green space and built-up area is basically the same, and the sharing degree from small cities to large ones continues to increase; the scaling factor of park area is the lowest, and the contradiction between supply and demand with population scale becomes more obvious as the city scale rises, which reflects that the sharing degree of parks is higher and that the total number of parks in large cities still has some spaces for improvement. 3) In terms of spatial and temporal characteristics, scaling factors have demonstrated the descending order of “Jiangsu > Zhejiang > Anhui” by administrative division, and the urban green space elements in different areas of a region follow the overall scaling law of the whole region. The differences are most significant in Anhui Province, where the distribution of urban green space factors from small to large cities is significantly unbalanced, while Jiangsu Province and Zhejiang Province are in a state of coordinated development where urban green space and population size complement each other. At the level of temporal characteristics, the same scale factor of urban green space elements in different provinces presents the tendency of assimilation, which is due to the combined effect of multiple factors such as the staged evolution of land use pattern in built-up areas and socio-economic development in the process of population urbanization, as well as the tendency of urban green space construction guided by the upper planning outline in a unified manner.
Conclusions The research reveals the scaling effect of urban green spaces and the spatial-temporal characteristics and internal laws of the scaling factors thereof. The scaling factors have non-linear characteristics in the scalar relationship between urban green space and population, which is a valuable supplement to the current evaluation indexes of per capita enjoyment based on linear relationship, and can help objectively quantify the local performance of different cities, and promote the refinement and improvement of relevant normative standards for urban green space planning based on related city-specific policies. The spatially convergent evolution pattern of the scaling factor of urban green space elements in the Yangtze River Delta reflects, to a certain extent, the response to the trend of coordinated regional development in the process of regional integration. The scaling factors gradually decrease in terms of time series, reflecting the transformation from incremental expansion to stock improvement of urban green space. At the level of specific elements, the differences and similarities in the scaling factors of various urban green space elements are the corollary of the different attributes of various green spaces. The above findings of this research could provide a scientific basis for the coordinated development of regional urban green space and population.
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