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 18,565 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 and 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.

Titus, Andrea
Wei, Hanxue
Babayode, Oyinkansola
Rom, William
Azan, Alexander