Influence of rooftop mitigation strategies on the thermal environment in a subtropical city

As one of the most promising climate adaptation measures, rooftop mitigation strategies (RMSs) have been studied and practiced in many cities. However, the cooling potential of RMSs may be controversial under different climates. This study establishes city-scale numerical simulations of RMSs, including green roofs (GRs), cool roofs (CRs), rooftop photovoltaic panels (RPVPs), and photovoltaic panels plus green roofs (PVPs+GRs) in Guangzhou, a subtropical city in China, to explore the impact of RMSs on the urban thermal environment during the clear-sky meteorological conditions. The results indicate that RPVPs and PVPs+GRs can cool the city throughout the day, especially from 12 to 17 LST, reaching 0.3–0.7 K, while GRs have the weakest cooling potential, only 0.1 K. The order of cooling space range is PVPs+GRs (the entire city) > RPVPs > CRs (urban and downwind areas) > GRs (urban area). RPVPs and PVPs+GRs mitigate the urban heat island (UHI) effect, reaching 0.5–0.6 K, and increase relative humidity (RH) by 8.5% and 9.6%, respectively. PVPs+GRs and GRs could increase specific humidity (SH) by 0.35 g/kg and 0.23 g/kg, respectively. RPVPs and PVPs+GRs reduce the universal apparent temperature (UAT) throughout the day, especially at night, reaching 0.8 °C (PVPs+GRs) to 0.9 °C (RPVPs), and hence improve human thermal comfort.