Trends in Cool Roof Solar Reflectivity Degradation in New York City (2014-2020): An Important Consideration for Health-Based Evaluations of High Albedo Urban Roofing Interventions

Luke Bonanni^1,2Anna Bershteyn³Mehdi Pourpeikari Heris⁴Andrea Titus³Hanxue Wei⁵Oyinkansola Babayode⁶William Rom^2,6Alexander Azan^2,3*

• ¹Department of Medicine, University of Pennsylvania Perelman School of Medicine, Philadelphia, United States
• ²New York University Department of Medicine, New York, United States
• ³Department of Population Health, New York University Grossman School of Medicine, New York, United States
• ⁴Department of Urban Policy and Planning, Hunter College, New York, United States
• ⁵Center for Urban Science and Progress, New York University Tandon School of Engineering, New York, United States
• ⁶New York University School of Global Public Health, New York, United States

Introduction: Growing remote sensing and machine learning capabilities offer opportunities to understand the spatiotemporal performance of reflective cool roofs, a widely implemented urban heat mitigation tool, in relation to health. We evaluated cool roof solar reflectivity trends across NYC and in heat-vulnerable communities. Methods: In this retrospective, longitudinal study, we used satellite-derived cool roof data aggregated to census blocks over 2014-2020. Roofs with a solar reflectivity value ≥ 65 in 2014 were defined as cool roofs with sufficient albedo. Cool roofs with subsequent reflectivity < 65 were considered degraded. We descriptively calculated the cumulative proportion of census blocks that experienced degradation across NYC and in low vs high heat-vulnerable areas defined by the NYC heat vulnerability index. Results: Of 18565 census blocks with at least one building with a cool roof installed and an average cool roof reflectivity ≥ 65 in 2014, 24.56% experienced degradation by 2020. A greater proportion of census blocks experienced degradation by 2020 in low (27.03%) vs high (21.20%) heat-vulnerable areas. The largest proportion of total, census block-level cool roof degradation occurred between 2014-2016 (57.39%). Discussion: We found strong evidence of cool roof degradation across NYC, which has important implications for future health-based evaluations. Interestingly, a larger proportion of census blocks experienced cool roof degradation in low compared to high-heat vulnerable areas, potentially highlighting the effectiveness of community-led environmental justice initiatives. Municipal maintenance initiatives are needed to ensure the urban heat mitigation potential of cool roofs is sustained.