Christopher Scarpone

The Urban Heat Island (UHI) phenomenon contributes to higher air temperatures of 1 to 50C in urban areas when compared to adjacent rural landscape. UHI affects the quality of life for inhabitants of cities by contributing to heat-related illness, exacerbating air pollution, and also results in increased electricity consumption for indoor air conditioning. Low albedo surfaces such as asphalt parking lots are a major contributor to UHI formation and occupy up to 5 per cent of land cover in North American cities. In this study, a true three-dimensional model is created to simulate the daily progression of shadow coverage cast by city trees growing to the south of an asphalt parking lot. Data collection occurred during three days with varying ambient temperature and solar radiation in Toronto, Canada during June 2012. Asphalt surface temperature was measured in a parking lot that received varying amounts of tree shadow. In situ temperature data were measured hourly at 440 locations using a 1 m grid; spot temperature values were then interpolated to a surface using ordinary kriging. Twelve temperature surfaces (8 am to 7 pm) were aggregated into three time intervals to represent distinguishable periods of solar intensity (8 to11 am, 12 to 3 pm, 4 to7 pm) in addition to one temperature surface representative of an entire day. Shadow persistence was highly negatively correlated with asphalt temperature during the solar intensity period 12 to 3 pm (r=-0.689 to -0.756, p<0.001) and for the entire day (r=-0.766 to -0.773, p<0.001). Average hourly ambient air temperature was found to be cooler under tree shade compared with above non-shaded parking lot 0.96 to 2.280C and 1.6 to 2.50C in these same periods, respectively. City planners can proactively lessen the impact of the UHI phenomenon by prioritizing afforestation efforts adjacent to asphalt parking lots, and especially by planting trees that cast shade on these surfaces between 12 and 3 pm.