The relationship between people and trees has long been a favorite subject of mine. That’s why urban forestry work – particularly in assessing and improving the urban tree canopy – is one of the most satisfying parts of our job. Maximizing the number of trees on urban land not only brings beauty to neighborhoods, but can also significantly cool the air during hot months, decrease energy use, improve water quality, and reduce noise.
Reducing “urban heat islands”
A sobering fact: More people in the U.S. die from excessive heat exposure than from all natural disasters combined.i During extreme hot weather events, the elevated temperatures in so-called “urban heat islands” are a major threat to human health. In urban areas, a significant portion of the tree canopy has been removed to make way for paved roads, parking lots, sidewalks, and buildings. Those impenetrable surfaces (e.g., asphalt, concrete, brick, and stone) absorb and hold thermal radiation from the sun. On a hot, sunny summer day, roof and pavement surface temperatures can be 50–90° hotter than the air, and those surfaces heat the air around them. Air temperatures in cities, particularly after sunset, can be as much as 22°F warmer than the air in more forested neighboring regions. And many city-dwellers live without air conditioning, so when temperatures soar, human health is put at risk.ii
A robust urban tree canopy can help. A well-known benefit of trees is their ability to reduce ground surface temperatures, both by direct shading and by transpiration. Trees can lessen heat island effects, especially when they shade building windows and rooftops, or pavement in parking lots and on streets. Since shaded surfaces may be 20–45°F cooler than the peak temperatures of unshaded materials, that can help reduce peak summer air temperatures by up to 10°F.iii
Improving stormwater management and water quality
In the concrete jungle, stormwater and surface runoff often has no place to go but into nearby streams, rivers, ponds, and lakes – along with the many contaminants it picks up along the way. Increasing the urban tree canopy reduces runoff by providing more foliage for the rain to land on and evaporate, and more surface soil to absorb and filter rainwater.
Reduced energy use and improved air quality
The EPA estimates that for every 1° F increase in summertime temperature, peak utility use in medium and large cities increases by an estimated 1.5 – 2.0 percent. Trees that directly shade buildings decrease the demand for air conditioning. By reducing energy demand, trees decrease the production of associated air pollution and greenhouse gas emissions.iv
The research is clear: more healthy trees make cities more sustainable and enjoyable. The Consulting Group at SavATree has experience with tree canopy assessment, planning, and management at multiple scales, from the site to the neighborhood, to the city and beyond.
Please contact me about how we can help you with tree canopy assessment, planning, and management:
Mike Galvin, RCA
Director, SavATree Consulting Group
i Environmental Protection Agency, “Heat Island Impacts: Compromised Human Health and Comfort,” accessed January 9, 2017, https://www.epa.gov/heat-islands/heat-island-impacts#health
ii Environmental Protection Agency, “Heat Island Impacts,” accessed January 9, 2017, https://www.epa.gov/heat-islands/heat-island-impacts
iii Environmental Protection Agency, “Heat Islands: Using Trees and Vegetation to Reduce Heat Islands,” accessed January 9, 2017, https://www.epa.gov/heat-islands/using-trees-and-vegetation-reduce-heat-islands
iv Environmental Protection Agency, “Heat Island Impacts,” accessed January 9, 2017, https://www.epa.gov/heat-islands/heat-island-impacts