Urban Green Infrastructure as a tool for urban heat mitigation: Survey of research methodologies and findings across different climatic regions

The combined trends of urban heat island intensification and global warming are focusing attention on greening of cities as a tool for urban heat mitigation. Our study examines the range of research approaches and findings regarding the role of urban green infrastructure (UGI) in mitigating urban heat and enhancing human comfort. It provides an overview based on 89 studies, carried out in a range of geographic and climatic regions. We surveyed the distribution of methodologies employed, spatio-temporal scales considered, type and extent of UGI, climatic variables studied and contribution of UGI to ambient air cooling and enhancement of human comfort. It was found that neither the differences in geographic location or in climate conditions had a significant impact on the choice of research approach. The studies, mostly done on limited spatio-temporal scales, have focused on the rate of air cooling by UGI, and to a lesser extent on its impact on thermal comfort. Maximum observed intensities of park cool island (PCI) effects typically ranged between 1.5 °C–3.5 °C, with no apparent correlation to climatic region. However, there is a tendency seen for larger green sites to induce a stronger PCI, whereas well-shading street trees also have a significant cooling and relieving effect.