Guest Contributor: George Profous, Senior Forester, Division of Lands & Forests, New York State Department of Environmental Conservation.
What was once dubbed the Urban Heat Island (UHI), is now ominously termed Extreme Heat. But whatever the terminology, trees can help to reduce this warming.
The increase in urban temperatures can be addressed by air conditioners, cooling centers, painted rooftops and individually planted shade trees. While these approaches make sense, dealing with effects only puts a temporary Band-Aid on the problem. The world is becoming increasingly urban, and this development influences heat distribution.
Trees are most valuable in our cities, where they shade streets, sidewalks, buildings and people. They increase the reflection of sunlight. In the few cases where they absorb a bit more sunlight than a lighter surface, they compensate by evaporating and transpiring water, providing even more cooling. Simply put, trees don’t get hot. No umbrella or awning behaves in the same way!
By shading building materials that absorb and re-radiate a lot of heat, trees cool the streets and the people on the sidewalk who are absorbing the re-radiated heat – and keep the nights cooler. Overall heat reduction from trees in cities from around 2 to 7 F during hot summer months are common. In the 2022 European summer heat wave, fatal heat stress occurred when 104 F daytime temperature were compounded by nighttime temperatures above 86 F, providing no break from the heat. Steps to decrease surface temperatures, which can be up to 45 F warmer throughout the day, prove critical to reducing nighttime temperatures.
In one study, temperatures in a 1.2-acre forested park (about the size of a football field) were 90 F in the treetops, 80 F at pedestrian height, and 104 F elsewhere. Estimated heat savings were 10,500 kWh per day or about 500 large air conditioning units operating daily.