Research Recap: Interaction of Urban Heat Islands and Heat Waves Under Current and Future Climate Conditions and Their Mitigation Using Green and Cool Roofs
Study Overview
The 2019 study Interaction of Urban Heat Islands and Heat Waves Under Current and Future Climate Conditions and Their Mitigation Using Green and Cool Roofs evaluated rooftop mitigation strategies in two distinct urban climates, New York City and Phoenix. Published in Environmental Research Letters, the research used advanced atmospheric modeling to examine how green and cool roofs influence urban heat island intensity during both typical summer conditions and extreme heat waves. By comparing current and projected future climates, the study assessed rooftop strategies not only for localized cooling but also for their broader interactions with urban heat dynamics under increasing thermal stress.
Key Findings
The study concluded that irrigated green or vegetative roofs were the most effective rooftop strategy for reducing urban heat island intensity in both cities, particularly during heat wave conditions. Evapotranspiration from irrigated vegetation provided cooling benefits that reflective roofs alone did not achieve at the same scale. Cool roofs delivered surface temperature reductions but showed more limited effectiveness at the city scale. Importantly, the performance of green roofs depended on sustained irrigation, maintenance, and favorable climate conditions. These findings reinforce that reflectivity alone is not a comprehensive solution and that mitigation strategies must be evaluated within operational and environmental constraints. Durable roof systems, including EPDM-based assemblies, provide stable long-term performance without reliance on water inputs or complex upkeep, supporting resilience under varied and extreme conditions.
Areas for Future Research
The study highlights the need for further research into the feasibility and long-term performance of rooftop mitigation strategies. Future work should examine water demand, maintenance requirements, and lifecycle impacts associated with irrigated green roofs, particularly in arid regions such as Phoenix. Additional research comparing embodied carbon, service life, and replacement cycles across roof systems would provide a more complete understanding of environmental tradeoffs. Field-based studies that integrate roofing membranes, insulation, and building operations would help move beyond modeled outcomes toward real-world performance data. These research needs align with broader efforts to evaluate roofing solutions through durability, longevity, and whole-system metrics rather than short-term thermal effects alone.
Applicability for Building Owners and Facility Managers
For building owners and facility managers, the study underscores the importance of matching rooftop strategies to operational realities. While irrigated green roofs can offer urban-scale cooling benefits, they introduce ongoing water use, structural considerations, and maintenance obligations that may not be practical or sustainable for many facilities. Roof systems designed for long service life, low maintenance, and repairability, such as EPDM assemblies, offer predictable performance and reduced lifecycle impacts. Owners benefit from solutions that manage risk, limit operational complexity, and minimize embodied carbon associated with frequent replacement. The findings support a performance-based approach that prioritizes resilience, sustainability, and long-term value within the broader context of building operations and climate adaptation.
Citation: Citation Mukul Tewari et al 2019 Environ. Res. Lett. 14 034002 DOI 10.1088/1748-9326/aaf431