Testing relationships of urban tree canopy and the built environment with temperature and human health in US cities

Heatwaves are the leading cause of death among natural disasters, and cities are regional hotspots due to the urban heat island effect. Many studies have connected excessive heat with poor human health and urban tree canopy (UTC) with good human health; however, most of these studies separate how trees impact temperatures, how temperatures impact health, and how trees impact health. In this study we simultaneously evaluate all three of these relationships sourcing data from US cities aggregated to the census tract-scale. Using Bayesian structural equation modeling, we draw paths connecting the urban biophysical conditions of UTC, impervious surface area (ISA), and built-up volume to land surface temperature (LST), and LST, UTC, ISA, and socioeconomic covariates ( i.e. , income, sex, and age) to heat-related human health measures. We ran the model at the US national-level, 6 climate zones, and 107 cities. The full model did not show good fit at any spatial level, suggesting relationships between UTC, ISA, or LST and health are unclear at the tract-scale. However, the urban biophysical conditions showed strong associations with LST across spatial levels with varying magnitudes by climate, which was clearest at the national- and climate zone-level. While the impacts of LST, UTC, and ISA on human health are unclear at the resolution of the census tract, UTC, ISA, and built-up volume drive LST with median regression coefficients of 0.30, -0.31, and 0.28 for the national model. The cooling from tree canopy and built-up volume and warming from ISA varies substantially by climate, however, emphasizing the importance of climate-specific, localized urban planning to manage urban temperatures in warming climates. The links from aggregate UTC, ISA, and LST to aggregate health in this cross-sectional study are not strong enough to observe at the tract-scale, so future studies could limit scope to finer spatiotemporal scales. ● A national assessment of urban tree and heat-related health was conducted in US cities ● Drivers of urban temperature vary across climate zones ● Cooling effect of urban tree canopy is stronger in dry climates ● Warming effect of impervious surface area is stronger in humid climates ● Urban tree canopy and temperature show no association with heat-related health at the tract scale