Not even past: Legacy effects of redlining on heat inequities across spatial scales in Philadelphia

초록

The enduring effects of historic redlining practices on urban landscapes and heat conditions have been documented in multiple U.S. cities. Systematic differences in land surface temperatures across Home Owners’ Loan Corporation (HOLC)-graded neighborhoods reflect this legacy. However, neighborhood-scale land surface temperature data typically lack the spatial and temporal resolution to capture micro-scale disparities in perceived heat. In this study, we examined heat disparities associated with redlining at two spatial scales in Philadelphia, Pennsylvania. We first followed a traditional approach by generating boxplots of land surface temperature, tree canopy cover, and building area across HOLC grades. We then used ENVI-met to compare near-surface air temperatures in detailed three-dimensional domains of matched census blocks from redlined and non-redlined neighborhoods. Finally, we developed three greening scenarios by installing trees and grass within census blocks in the redlined neighborhood to identify the most effective cooling strategy. We found that (1) ‘D’-graded neighborhoods have higher land surface temperatures and more heat-exacerbating outdoor built environments; (2) census blocks in the redlined neighborhood consistently record elevated near-surface air temperatures throughout the day; and (3) integrating trees and grass produces the most effective cooling while using either alone yields moderate, site-dependent effects. These findings suggest that unequal heat exposure, linked to the legacy of redlining, persists across spatial and temporal scales and that multilayer greening is effective in addressing these entrenched inequalities. Rather than broadly promoting green infrastructure in marginalized neighborhoods, efforts should prioritize targeted, publicly led interventions tailored to local built environment conditions. © 2026 Elsevier Ltd

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