Mitigating the Urban Heat Island Effect with Cool and Green Roofs: A Case Study on a Heat Wave Event in the Kansas City Metropolitan Area

Urban heat islands (UHI) have been shown to have detrimental effects on the environment and the health of those living in cities. An UHI is a phenomenon where temperatures within cities become warmer than those of the surrounding rural areas, especially at night. As urban land cover expands with the rapidly increasing urbanization worldwide, the extent of cities’ UHI will also expand. In order to combat the rising temperatures, both cool and green roofs have been proposed as effective methods of mitigating the UHI effect. Cool roofs increase the albedo of a structure through the installation of light-colored roofing materials, which, in turn, reduces the amount of solar radiation that is absorbed at Earth’s surface. In contrast, installation of green roofs consists of the addition of soil and vegetation on a building, which increases the magnitude of the cooling effect from evapotranspiration. In our study, we examine the impact of widespread deployment of cool and green roofs on the UHI effect in the Kansas City metropolitan area during a heat wave in July 2012. The Weather Research and Forecasting (WRF) model will be employed in order to meet the proposed aim of this study. WRF is coupled to a single-layer urban canopy model that accounts for physical processes occurring within urban areas. All simulations will consist of three one-way, nested domains with spatial resolutions of 9, 3, and 1 km, from outermost to innermost, respectively. For cool roofs, roof albedo in the built-up area will be increased from 0.3 in the control simulation to 0.8 in the experimental simulation. A suite of four green roof simulations will be conducted with increasing amounts of vegetation covering urban roofs, including 25%, 50%, 75%, and 100% green roof fractions. Only results from the innermost domain will be analyzed.