Comparison of Different Blue-Green Infrastructure Strategies in Mitigating Urban Heat Island Effects and Improving Thermal Comfort

Urban heat island (UHI) as one of the major consequences of urban development has been extensively studied. Various strategies have been proposed to mitigate the UHI effect. Particularly, the blue-green infrastructure (BGI) using vegetation and water bodies for environmental cooling have received growing attention. However, there are limited publications on the microclimatic effects in the vicinity of river corridors in urban areas and strategies to improve thermal comfort. Using a restored urban stream as a case, this research aims to evaluate the effectiveness of different strategies on thermal performance, including the expansion of water coverage, addition of vegetation, and conversion of the original concrete riverbed into porous substrate. A micro-scale computational fluid dynamic (CFD) model was used to simulate the diurnal profiles of the river corridors. Using the Universal Thermal Climate Index (UTCI) as an indicator, the study found that street trees are associated with the average lowest values of UTCI during the daytime, while using porous substrate can also reduce UTCI with a maximum UTCI reduction of 3.46°C. However, during the hottest hours of the day, porous substrate even causes an increase in UTCI by reflecting more short-wave radiation. This finding also provides the general procedure of evaluating the relationship between BGI optimization strategies and outdoor thermal comfort.