Green blocks are up to 4 degrees cooler than treeless streets

A new study from the Healthy Green Spaces Coalition reveals that city blocks with more trees are significantly cooler than blocks without shade, highlighting the importance of tree canopy for reducing the urban heat island effect. 

"This study links a 65-city urban heat island dataset with American Forests’ Tree Equity Score file for every urban census tract in those cities. For each tract (a neighborhood-sized geography), we matched its heat island intensity in degrees Fahrenheit above a nearby rural baseline to its tree canopy percent and related equity indicators, using the shared census tract GEOID (the unique Census identifier for each tract)." Nationally, the greenest tracts averaged close to a one degree difference from the least green tracts, amounting to roughly 9% less excess heat. 

In some cities, that gap reaches 20% to 40%. "On a series of extreme heat days, a one‑degree shift in ambient conditions can mean the difference between 'very hot' and 'dangerous,' especially for people with health risks." 

While the study is isolated to trees, other factors impact the temperature of cities including lawns, natural turf, and other vegetated ground covers. "We do not quantify those turf and lawn effects in this study, so the cooling dividend we report for trees should be read as conservative: in many neighborhoods, additional cooling from ground‑level vegetation, parks, and other green infrastructure sits on top of the canopy effect."