One way trees lower urban temperatures is by shading heat-absorbing surfaces. Credit: Priya Jaishanker
Cities contain numerous hard surfaces (concrete, asphalt, metal, and brick) that absorb large quantities of solar radiation (heat) throughout the day, slowly releasing this heat overnight. The abundance of these surfaces make cities noticeably warmer than the surrounding countryside. The excess heat discourages people who live and work in cities from enjoying the outdoors during the warmer parts of the year.
This effect is significantly reduced, however, when absorptive surfaces are shielded from receiving direct sunlight. Trees planted in urban areas provide invaluable shade by blocking sunlight from reaching absorptive surfaces and cooling by a process called evapotranspiration- leads to the natural cooling of surrounding areas through water evaporation. This reduction in temperature allows people to more comfortably spend time outside. Some absorptive surfaces, like automobiles release volatile organic compounds, or VOCs, when they get hot. These compounds are atmospheric chemicals that react to form ozone, a compound that can contribute to both the development of human respiratory disease and the progression of global warming. Tree shade over cars reduces the production of VOCs, helping maintaining urban air quality.
Watch Urban Forests Role in Heat Reduction to learn more. This video is part of a series, Trees for Energy Conservation, developed by the Southern Regional Extension Forestry and Virginia Tech Cooperative Extension with funding provided by a National Urban and Community Forestry Advisory Council grant.
Written by: Connor McDonald and Holly Campbell, Southern Regional Extension Forestry