Cooling effects of urban green spaces: A systematic review of methods applied in the past two decades

Research on the cooling effects of Urban Green Spaces (UGSs) has increased rapidly in recent years to address the pressing issue of Urban Heat Island (UHI). Several review papers have conducted literature review focusing on various perspectives, such as landscape metrics and correlation analyses. However, a thorough review of the methods and their components applied in this field has yet to be conducted. This review paper identifies and examines 215 relevant papers selected through the PRISMA standard, yielding several key findings. Firstly, from a temporal aspect, research in this field has grown since 2017, with a notable acceleration after 2021. Geographically, studies are concentrated in China, the USA, India, and European countries. Secondly, regarding used methods, while most studies tend to employ a single method, more recent research has begun to integrate multiple methods. Furthermore, we also found that remote sensing data can be applied across most common methods, including regression and correlation models. In contrast, certain methods, such as simulation models, are typically associated with ground-based data. Overall, this review is the first to conduct a comprehensive analysis of the methods used and their components from both a temporal and quantitative perspective. It also identifies the associations between used data, variables, and methods, and how they influence selections of each other. The findings can assist future studies in identifying appropriate methods based on their research contexts.