Micrometeorological simulations to predict the impacts of heat mitigation strategies on pedestrian thermal comfort in a Los Angeles neighborhood

Urban heat islands can increase energy use, affect human health and thermal comfort. A study investigated the effectiveness of heat mitigation strategies regarding thermal comfort in an eastern Los Angeles County neighborhood. A series of micrometeorological simulations for an extreme heat day were conducted. For each heat mitigation strategy, the physiological equivalent temperature (PET) was used to quantify the thermal comfort of pedestrians. Analysis focused on four mitigation strategies: solar reflective ‘cool roofs’, vegetative ‘green roofs’, solar reflective ‘cool pavements’, and increased urban vegetation. Findings revealed that the conversion of existing streets to cool pavements considerably decreased surface air temperatures. However, cool pavements also reduced the thermal comfort of pedestrians during the daytime due to increases in reflected shortwave radiation. Roof-level heat mitigation strategies were less effective at reducing surface air temperatures than street-level strategies. Street-level trees were also found to decrease surface-level air temperatures, albeit to a lesser degree. Finally, roof-level heat mitigation strategies were once again less effective than the street-level strategies for lowering the thermal comfort of pedestrians.