Multiscale Evaluation of the Cooling Effect of Greenspace in Urban Environments

Urban greenspace is an effective approach to reducing urban heat island (UHI) effects and providing comfort to the nearby occupants. In this study, a multiscale evaluation of the cooling effect of different types of greenspaces was conducted. Studies were conducted among four typical urban communities in two densely urbanized cities - Hong Kong and Singapore. Large-scale land surface temperature (LST) of pixel-level were retrieved from cloud-free satellite images. Long-term hourly meteorological data collected from weather stations was used for validating the LST retrieval results. Based on LST data at the macro-scale, and microclimatic modeling using simulation tools (ENVI-met) at the micro-scale, this study evaluated the performance of different types of greenspaces in cooling the environment of several typical urban communities. For the street-level greenspace, how the major characteristics of greenspace affect the cooling effect of greenspace was identified. Results demonstrate that the cooling effect of greenspace improves logarithmically with an increase in its size and density. Especially, the leaf area index (\(LAI\)) plays a major role in cooling the surrounding environment with the R² between \(LAI\) and the maximum local cool island intensity (MLCII) reaching 0.30 in Hong Kong and 0.33 in Singapore. For the green infrastructure, the simulation results indicate that street trees, green façades, and extensive/intensive green roofs are helpful in reducing air temperature and improving outdoor thermal comfort in the daytime. Among all scenarios, street trees are most effective to reduce air temperature and improve outdoor thermal comfort at the pedestrian-level. In densely populated urban areas, green infrastructure (especially green façade) may be a suitable choice for UHI mitigation, thermal comfort improvement, and cooling energy savings.