Published in: Urban Climate Volume 31
The Urban Heat Island (UHI) effect, defined as the temperature difference between urban and rural areas, is caused by the increased absorption and storage of solar energy by artificial surfaces as compared to natural vegetation. In addition to surface material, the urban form and wind direction also affect the UHI intensity. A model was developed to study the effect of various cool surface strategies on the microscale UHI intensity for hypothetical urban blocks in Chicago, USA. The statistically warmest hour of the year was analyzed for eight wind directions, whose probabilities were obtained from existing climatic data. Pavements, walls, and roofs with high albedo and high diffusivity had the lowest UHI intensity, approximately 0.05 ∘ C above the mesoscale intensity, while those with low albedo and low diffusivity had the greatest increase of about 0.6 ∘ C. The UHI intensity varied with spatial location within the urban area because of constricted airflow. The UHI intensity of an urban canyon averaged over the probability of wind blowing from different directions, was found to have a strong correlation ( R = 0.94) with the probability that it is an interior canyon that experiences lower wind speed on account of turbulent dissipation.