Geoengineering Cities with Reflective and Pervious Surfaces

The Urban Heat Island (UHI) effect, which causes urban areas to be warmer than the adjoining countryside, has been observed and studied for over two centuries. However, the synergistic effects of climate change and UHI have led to a greater urgency to mitigate UHI as cities across the world experience record-breaking heat. Fundamentally, the UHI effect is caused by changes in the energy balance of artificial surface such as asphalt and concrete as compared to natural surfaces such as soil and vegetation. Moreover, changes in urban form due to the construction of urban canyons also affect the wind speed in urban areas, further changing the heat balance. Reflective and pervious surfaces are two geoengineering techniques in which the fraction of absorbed solar radiation is decreased while the fraction of latent heat is increased, respectively. Both of these have the potential to mitigate the UHI effect, but their effectiveness depends on their durability as well as the surrounding urban form. Solutions for mitigating UHI must consider not just changes in energy balance, but also their durability and the influence of urban form to maximize their effectiveness.