Optimization of urban cooling network informed by actual flow of cooling service provided by urban green space from a 3D perspective

Urban green space (UGS) optimization is an effective nature-based solution for mitigating thermal discomfort due to its Spillover Effect of Cooling Service (SECS). Previous studies have focused on the internal structure and external connectivity of UGSs, but often neglected the hindering effect of dense buildings on SECS. Taking Lanzhou, a typical valley city in northwestern China, as a case study, this study constructed and optimized a UGS cooling network informed by the actual flow of cooling service from a three-dimensional (3D) perspective. It firstly quantified UGS SECS and its driving mechanism using time-series data, field measurements, and UAV (Unmanned Aerial Vehicle) images, identified cooling sources through SECS and morphological spatial analysis, developed a resistance map based on building height, façade and volume, and further optimized the cooling network using circuit theory and complex network analysis. The results suggested that 1) UGS inner characteristics of area, shape and vegetation abundance and surrounding ventilation effectively explained the driving mechanism of SECS, with explained variances of 77.34 % and 70.62 % for cooling intensity and range, respectively. 2) Cooling sources were mainly located on the urban fringe, while riverside UGSs exhibited higher SECS and contributed more to landscape connectivity than those within downtown area. 3) Ventilation resistance was generally higher in downtown areas, particularly in the eastern parts with dense buildings and residents, resulting in fewer cooling corridors. 4) Optimization suggestions for cooling network were proposed to reduce detected barrier areas and improve topological structure. This study provides theoretical references for the nature-based mitigation of urban thermal stress.