Global urban green spaces in the functional urban areas: Spatial pattern, drivers and size hierarchy

Abstract

Urban green spaces (UGS) play a vital role in the urban eco-environment and are essential for human well-being. However, the spatial heterogeneity and size hierarchy of UGS, as well as the driving factors in geographically remain unclear. This study applies the rank-size law to elucidate the multi-scale distribution patterns of UGS in functional urban areas worldwide. Subsequently, the gradient boosted regression tree method was used to quantitatively analyze the contributions and thresholds of natural environmental and socioeconomic factors influencing UGS. The results indicate that: (1) Globally, the top 20 % of cities in terms of UGS area represent nearly 60 % of the total urban green space. Developed regions like North America and Europe tend to have more extensive and larger UGS, whereas developing and rapidly urbanizing regions like Asia and Africa have more compact and smaller green spaces. (2) The rank-size distribution of UGS can be explained to some extent by Pareto's law and the size hierarchies of UGS and FUAs are highly consistent. (3) Area of UGS is more closely related to urban area rather than the population it serves. (4) Socioeconomic factors have a significant impact on UGS, exerting a dominant influence on both UGS area (UGSA) and per capita UGS area (PUGSA). Specifically, the human development index and impervious surface percentage contribute 61.51 % to UGSA, with all socioeconomic factors collectively contributing up to 68.59 %. For PUGSA, socioeconomic factors contribute 63.07 %, while three natural environmental factors contribute less than 37 %. These findings offer valuable insights for urban ecological construction aimed at promoting sustainable urban development, ensuring equitable green space resource allocation, and enhancing urban living environments.