A quasi-experimental approach for evaluating the heat mitigation effects of green roofs in Chicago, Illinois

Abstract In the coming decades, millions of urban residents will be exposed to increasingly deadly heat extremes. As an adaptive response to rising temperatures, many cities have begun to install vegetated ”green” roofs, which now vary widely in structure and size, and have generally been shown to have cooling capacity. Yet, little research has been done to differentiate which types of green roofs are most effective at reducing urban heat. We present a method to evaluate the cooling effects associated with green infrastructure that draws on publicly available satellite imagery and open-source software for analysis. Based on a quasi-experimental research design that integrates social and physical science approaches, this technique is able to identify the cooling effects of green infrastructure against background warming trends associated with urbanization and climate change. We demonstrate this method at three green roof sites across the City of Chicago, finding that the study sites with larger, intensive green roofs accompanied by diverse plant species have greater cooling benefits than the extensive, monoculture green roof. Our low-cost method can aid policymakers and planners in empirically evaluating the cooling capacity of green roofs in their own communities.