The effects of street tree planting on Urban Heat Island mitigation in Montreal

The effects of climate change and Urban Heat Island (UHI) phenomena have raised the attention for monitoring and evaluating the outdoor thermal comfort. The urban vegetation system is playing a significant role for UHI mitigation and adaption. The fraction of the ground covered by trees and other vegetation is smaller and contains less biomass than in nonurban areas. The absence of vegetation impacts the UHI in several ways, since vegetation, and in particular trees, intercept solar energy, and their shade reduces the temperature of surfaces below while increasing the latent heat exchange for the evapotranspiration process. In this paper, the common tree types and the size of trees in Montreal are investigated; and the effect of tree size and space between trees on outdoor comfort are compared by using environmental simulation. It's demonstrated that, the correlation (R²) between tree cover (SVF) and urban Ta is about 0.64 at summer mid-night. In the daytime, tree cover could reduce air temperature at the tree level (4 °C at 20 m height from the ground), as well as higher level (2 °C at 60 m from the ground).