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Urban heat islands (UHIs) exacerbate thermal stress, disproportionately affecting communities with limited tree cover. While satellite-derived land surface temperature (Ts) is widely used to assess urban heat, it often overestimates conditions compared to air temperature (Ta) —the metric more relevant to human thermal comfort. Despite this discrepancy, relatively few studies have leveraged Ta to quantify the cooling effect of tree canopy in heat-prone areas. Using a citywide network of high-accuracy air temperature sensors and high-resolution satellite data during a heatwave, we first show that surface UHI (SUHI) overestimates urban heat by a factor of two, with SUHI averaging 8. 9 °C ± 1. 2 vs 4. 6 °C ± 1. 1 for canopy UHI. We find that tree canopy cover is the dominant cooling factor, explaining 67% of the spatial variation in Ta. Notably, a 10% increase in tree canopy reduces air temperature by 0. 8 °C, while a 30% increase lowers it by as much as 1. 5 °C. These findings underscore the essential role of urban greening in mitigating extreme heat, reinforcing the need for targeted tree-planting strategies in vulnerable neighborhoods. By bridging remote sensing with in-situ temperature observations, our study highlights the urgency of integrating air temperature–based UHI assessments into urban planning and climate adaptation policies. Expanding tree canopy coverage is a scalable, nature-based solution for enhancing urban resilience, and this work directly quantifies its impacts.
Zaerpour et al. (Mon,) studied this question.