Numerical Assessment of the Impact of Roof Albedo and Thermal Resistance on Urban Overheating: A Case Study in Southern Italy

Urban heat island (UHI) and global warming effects increase the urban ambient temperature. During recent years, heat mitigation strategies have been implemented through experiments and simulations due to the significant impacts of these phenomena, especially on near-surface air temperature. UHI mitigation may help cities adapt to the future effects of increasing local air temperature, which are crucial especially in tropical cities. The impact of increasing roof albedo as a UHI mitigation strategy coupled to roof renovation with different performance levels was evaluated in the center of Palermo (Italy) as a case study. To this aim, ENVI-met (version 4.4.5) was used. In addition, three different thermal transmittance scenarios and four albedo scenarios (from 0.1 to 0.9) related to roofs were compared to simulate the efficiency of the roofs at the peak hour on the hottest day of a typical summer heatwave in terms of reduction in air temperature. Based on the results, changing the albedo of the roofs in the selected area led to a decrease in air temperature. The most obvious temperature drops of 0.37 °C were recorded in the scenario where the non-insulated roof was applied, while it was around 0.20 °C in other scenarios. Finally, changing roof albedo can have a limited impact on UHI if coupled with high roof thermal resistance.