Observed inequality in thermal comfort exposure and its multifaceted associations with greenspace in United States cities

Increasing exposure to heat stress threatens the health and well-being of urban residents. However, existing studies on measuring human thermal comfort exposure remain uncertain without considering fine-scale human-heat interaction and its long-term dynamics. To inform this issue, we proposed a population-weighted exposure assessment framework with the integration of high-resolution land surface temperature and population data to evaluate human exposure to thermal comfort and the associated inequality across 398 major cities over 2000–2020 in the United States, and further explored the multifaceted associations between greenspace and thermal comfort. Results show that 199 United States cities (50.00 %) experience severe heat stress (i.e., thermal comfort exposure <0.44) and 99 of which (24.87 %) are unevenly exposed to heat stress (i.e., Gini index of thermal comfort exposure >0.36). Temporal analysis from 2000 to 2020 reveals that human exposure to thermal comfort decreases by a mean magnitude of −0.00081 yr−1, and the associated inequality level decreases by a mean magnitude of −0.00153 yr−1. By linking urban greenspace and heat exposure, we find that greenspace has multifaceted associations with heat stress, with a highly positive correlation between greenspace and thermal comfort (i.e., comfort regulation by physical cooling effect) and a coincided exposure inequality between greenspace and thermal comfort. This study offers an alternative framework to characterize fine-scale human exposure to thermal comfort across space and time, provides observational evidence of thermal comfort exposure inequality in the United States cities, and highlights the need for prioritizing greening policies and actions to mitigate heat stress and exposure disparity.