Optimizing urban blue-green space in climate adaptive planning: a systematic review of threshold value of efficiency thresholds

ContextAlthough various methods exist to mitigate the urban heat island (UHI) effect, urban blue-green spaces (UBGS) are considered particularly effective. Understanding the threshold value of efficiency (TVoE) for UBGS can optimize urban land use and spatial planning.ObjectivesThis study systematically reviews the TVoE of UBGS to provide urban managers and landscape designers with comprehensive insights for climate-adaptive planning. We aim to summarize the distribution patterns and influencing factors of the TVoE, identify current research limitations and future directions and offer planning and research recommendations.MethodsWe conducted a systematic literature review (SLR) following the PRISMA guidelines, analyzing publications on the TVoE of UBGS from the Web of Science, PubMed, and Scopus databases.ResultsThe distribution patterns of the TVoE of UBGS are influenced by spatial types, latitude, and climate. Generally, the TVoE of urban green spaces (UGS) increases with decreasing latitude and increasing humidity, whereas the TVoE of parks and urban blue spaces (UBS) decreases with decreasing latitude and increasing humidity. The studies reviewed focus on the impact of landscape features of UBGS on cooling effects, while patch surrounding environmental and meteorological factors are less frequently mentioned. Cost-effective urban planning should prioritize UBS with complex shapes in low-latitude, humid regions, while in high-latitude, arid areas focusing on UGS with regular shapes. Future research should explore vertical structures within UBGS, surrounding environmental factors, and Local Climate Zones (LCZ) to enhance understanding of climate-adaptive planning.