Analysis of the cooling effects of higher albedo surfaces during heat waves coupling the Weather Research and Forecasting model with building energy models

In this paper, the numerical Weather Research and Forecasting (WRF) model is coupled with a Building Effect Parameterization (BEP) and Building Energy Model (BEM) to investigate the effects on the urban microclimate and building energy demand of increasing the albedo of urban surfaces. For the scope of this study, while the WRP performs real-data applications numerical weather prediction, the BEP serves to predict the heat and moisture fluxes from the urban canopies to the atmosphere and the BEM simulates the effects of anthropogenic heat emissions. As such the overall simulations are capable of taking into account the several factors that influence the urban microclimate and couple their mutual interactions. Outdoor microclimate results for the air temperature and wind speed are compared against measurements in Toronto, ON, during the 2018 heatwave period. The validation confirms the reliability of the WRF model and the selected approach. Then, in order to assess possible urban heat island mitigation strategies, the albedos of roofs, walls, and ground surfaces are increased from 0.2 to 0.65, 0.60, and 0.45, respectively. Results show that the maximum decrease in air temperature through these higher albedo values is nearly 2 °C at noon with a slight increase in wind speed. Moreover, the daily averaged decrease in the urban surface temperature and in the absolute humidity is 3.3 °C and 0.6 g/kg, respectively. Increasing the surface albedo would reduce the solar radiation balance at noon by almost 30 W/m2. Finally, the combined effect of decreased solar heat gains by urban surfaces and decreased air temperature would reduce the cooling energy demand by almost 10%.