Reevaluating how tree canopy cools the air and surfaces in cities at very high resolution

Abstract

Trees mitigate urban heat, but the extent of cooling, particularly for air temperature, remains uncertain. Many studies report strong cooling using satellite-derived land surface temperature (LST), but this metric overestimates the cooling relevant to human health and comfort. Additionally, such studies often rely on single-variable, canopy-only models and moderate resolution data that has not been validated in densely built-up areas. These data and modeling issues may further inflate estimates of tree cooling efficiency. Using >675,000 mobile air temperature observations from 11 Northeastern U.S. cities, we found that tree-induced air cooling was significantly lower than LST cooling. Cooling efficiency was highest in areas with substantial existing canopy, challenging recent reports of strong cooling in low-canopy areas. Impervious surface cover and water bodies controlled local surface and air temperatures as much or more than vegetation. These findings highlight the importance of high-quality data and multipronged urban heat mitigation strategies, integrating clustered tree planting, impervious surface removal, and other complementary measures.