Enhancing the cooling effect of urban green infrastructure: An empirical analysis of interactive impacts and optimizing pathways over 310 Chinese cities

Urban green infrastructure (UGI), an effective nature-based solution for urban sustainability, is also crucial in coping with the prevalent urban heat island (UHI) effect. However, how to enhance its cooling effect through optimized spatial patterns (e.g., city-level structure and network) has received little concern. Based on 310 Chinese cities, this study explored the multi-dimensional features of UGI and their interactive and conjoint impacts on surface UHI (SUHI) to identify the optimized cooling pathways under specific climatic backgrounds. In particular, the patterns of UGI were characterized by eight dimensions, i.e., quantity, patch size, shape complexity, fragmentation, contiguity, diversity, structure, and connectivity, each using one representative metric. Then the complex pathways of how UGI affected SUHI were investigated using the structural equation model, with the potential moderating role of climatic backgrounds taken into consideration. Results revealed that UGI affected SUHI through diverse pathways, and each pathway covered discrepant UGI features with various influencing directions and magnitudes. Among all pathways, direct impacts surpassed indirect ones, whose performances were largely diminished by multiple complex and counteracting mediation effects. Coverage, contiguity, structure, and connectivity, with the latter two dimensions largely neglected by previous studies, were found to be the primary cooling features. Among them, connectivity, despite its dominated impact in direct pathways, remained at low levels due to limited consideration and poor execution in previous planning practices. Typically, with the same UGI coverage, cities equipped with more clustered structure and connected network exhibited relatively lower SUHI intensity. For most cities, such enhanced cooling benefits can be achieved through mediation effects by smaller patches, more complex shapes, and shorter inter-patch distances. For cities in tropical and subtropical regions facing severer heat issues, however, it is recommended to optimize UGI design by adopting simple and regular patches with scattered distribution. This study extended the understanding of how to configure UGI for enhanced cooling effects from local to city level. The results may benefit urban planners pursuing climate resilient cities.