The urban heat island (UHI) effect is often defined as the thermal enrichment of air in urban environments due to the presence of traditional urban infrastructure and human activities. As urban areas develop, vegetation which contributes to evapotranspiration and thus cooling of the outdoor air is replaced with low-albedo, or low-reflectivity, surfaces that absorb heat. Green infrastructure, including green roofs and bioretention cells, is typically designed for stormwater treatment but its co-benefits may include mitigation of the UHI effect by increasing plant density and reducing the presence of low-albedo surfaces such as shingled roofs and asphalt pavements. Seven bioretention cells and five green roofs in four distinct neighborhoods of Columbus, Ohio, were outfitted with sensors to record air temperature every minute at ground level and two feet above ground surface. Each treatment site was compared with a nearby control site containing a traditional rooftop or road with identical measurement techniques. The bioretention cells, green roofs, and their controls all had varying characteristics including size, design, surrounding land use, and plant species and density. Statistical testing showed significant differences between the treatment and control at every site aside from one green roof at ground level and a second green roof at a two-foot measurement height. Location and local building material characteristics may have contributed to certain temperature reading differences. Bioretention cells and green roofs have the capacity to mitigate the UHI effect to a noticeable degree and thus UHI effect mitigation should be considered as a possible co-benefit.
