Pavement geometry in microscale urban heat Islands

The Urban Heat Island (UHI) phenomenon has been observed in hundreds of cities across the world, which have been shown to be warmer than adjacent rural areas. Within a city however, the heterogeneity and large number of variables acting simultaneously can make it difficult to understand how UHI develops at a microscale. Urban roads can have different materials and layered structures (collectively called ‘pavement geometry’) in a city and can also be positioned differently with respect to the urban form. A three-factorial analysis was performed using an uncoupled pavement-3D urban canyon model to investigate how pavement geometry, urban form, and meteorological conditions affect microscale UHI. Representative temperature data from Chicago, USA was obtained and the UHI in a simulated urban area was evaluated for the warmest and coldest hours of the year. During the warmest hour, urban form and pavement geometry could increase the microscale UHI by an additional 3℃ at distinct spatial locations. Whereas, during the coldest hour which included no sunlight, urban form played a more significant role to locally increasing the UHI by 1 to 1.5℃. Additionally, in closed urban canyons with constricted wind flows, pavement geometry has a particularly important role to play, whereas in more open spaces, the wind flow pattern affects the UHI. Ultimately, multiple microscale UHI case studies are recommended for individual cities to factor in the large number of site-specific variables.