The Power of Urban Trees

KEY CONCEPTS

• America’s growing urban population is particularly vulnerable to extreme heat, heavy rainfall, and poor air quality—all amplified in a warming world.

• Climate Central’s new report, The Power of Urban Trees, explains how trees can alleviate impacts from urbanization and help communities adapt to climate change.

• By cooling air and surface temperatures, trees reduce the health hazards of extreme heat. 

• Trees also slow and soak up rainfall; filter the air; and absorb harmful carbon pollution.

• Climate Central analysis using the U.S. Forest Service’s i-Tree data shows the estimated annual benefits of urban trees in 242 U.S. cities (defined by county or counties).

Download local data
Read the full report

Around 80% of Americans live in urban areas, and this could jump to nearly 90% by 2050. As urban populations expand, so do concerns about climate risks in cities. Built environments can boost risks associated with extreme heat and heavy rainfall events made more likely in a warming world. 

Cities are generally warmer than surrounding landscapes due to the urban heat island effect, which occurs because pavement and buildings retain heat and reflect it back into the surrounding air. Paved surfaces also don’t absorb rainwater, and are therefore prone to flooding from stormwater runoff.

Concentrated human activity (especially traffic) in urban areas contributes to poor air quality. Burning fossil fuels releases greenhouse gases and other tiny particles into the air, which can cause severe health hazards. Cities contribute up to 60% of total greenhouse gas emissions across the globe. 

The power of urban trees

Cities are incorporating nature into their infrastructure to help alleviate impacts of urbanization and build resilient communities. A growing body of research shows that urban forests—the trees in cities and surrounding communities—and other greenspaces can help cities adapt to climate change. 

Trees provide critical benefits in an increasingly warmer and urbanized world. Trees help communities:

• Reduce heat. Trees reduce the risks of extreme heat, the leading weather-related cause of death. Tree canopy helps reduce surface temperatures and cool the air by shading heat-absorbing buildings and pavement. Shade trees also provide immediate relief for people working, playing, or exercising outdoors.

• Avoid flooding from stormwater runoff. Tree canopy slows rainfall, while roots and soil filter and absorb water—minimizing the amount of stormwater that flushes over pavement and contributes to runoff and flooding.

• Improve air quality. Leaves absorb harmful gases such as ozone and nitrogen dioxide, and intercept hazardous particulate matter that pollute the air.

• Remove and store greenhouse gases. Trees remove CO2 and other greenhouse gases from the atmosphere. They absorb CO2 during photosynthesis and store the carbon in their biomass (including their leaves, trunks, branches, and roots).

• Protect health and provide connection to nature. Studies have linked trees and time spent in nature to a number of physical and mental health benefits. 

Climate Central’s new report further explains “The Power of Urban Trees” and discusses how communities can protect and support urban forests to continue benefitting from them.

Measuring urban tree benefits

The U.S. Forest Service and partner organizations developed i-Tree—a series of free web tools that map and measure urban forests and their benefits. Climate Central summarized i-Tree data to estimate annual tree benefits for 242 cities (defined by county or counties) across the continental U.S. 

• Each year, trees across these counties help avoid about 110 billion gallons of stormwater runoff (equivalent to nearly 167,000 Olympic-sized swimming pools).

• These urban trees also reduce nearly 4 billion pounds of air pollution and absorb roughly 150 million tons of carbon dioxide equivalent (or CO2e, including CO2 and other greenhouse gases) annually.

• The top three most populous cities in the analysis—Los Angeles (Los Angeles County), New York City (across five counties), and Chicago (Cook County)—rank among the biggest contributors of global greenhouse gas emissions. Collectively, trees across these counties help absorb approximately 1 million tons of CO2e each year (equivalent to the annual GHG emissions from about 192,000 cars).

• Top-benefitting counties are spread across the country, but a few locations appear more than once at the top of the rankings, including: Aroostook and Penobscot Counties in Maine; Lane County, Oregon; and Humboldt County, California

*Based on annual estimates of benefits from the U.S. Forest Service i-Tree tools.

Download local data for all 242 counties.

LOCAL STORY ANGLES

Explore tree canopy and related benefits in your neighborhood, city, county, or state.

The data-rich i-Tree web tools allow users to measure local tree canopy at different scales, from individual trees to urban forests across an area. Explore numerous variables ranging from health outcomes to economic benefits. Users can review support resources or join periodic training sessions hosted by the i-Tree support team to learn more about the tools’ capabilities. 

Assess the equity of trees and nature access in your area.

The non-profit organization American Forests developed Tree Equity Score maps to quantify tree equity in cities across the U.S. and inform community planning. The Trust for Public Land provides a ParkScore for the top 100 most populated cities and ranks locations based on key variables related to greenspace access. 

CONTACT EXPERTS

Hosted by SciLine, urban forestry expert Dr. Vivek Shandas from Portland State University will be available for interviews on Thursday, May 4, from 2-3:30 p.m. ET. Click here for more information.

Jason Grabosky, PhD
Professor
Department of Ecology, Evolution, and Natural Resources
Rutgers University
Relevant expertise: urban forests
Contact: grabosky@sebs.rutgers.edu 

Jason Henning, PhD (he/him)
Research Urban Forester
The Davey Institute
Relevant expertise: i-Tree tools, urban forest assessment
Contact: jason.henning@davey.com 

David J. Nowak, PhD
Emeritus Senior Scientist (Retired)
US Forest Service, Forest Inventory and Analysis
Relevant expertise: urban forest inventories and ecosystem services
Media Contact: Sharon Hobrla, sharon.hobrla@usda.gov

FIND EXPERTS

Contact the federal urban forest program manager for your area, or find your state coordinator.

Submit a request to SciLine from the American Association for the Advancement of Science or to the Climate Data Concierge from Columbia University. These free services rapidly connect journalists to relevant scientific experts. 

Browse maps of climate experts and services at regional NOAA, USDA, and Department of the Interior offices.  

Explore databases such as 500 Women Scientists, BIPOC Climate and Energy Justice PhDs, and Diverse Sources to find and amplify diverse expert voices. 

Reach out to your State Climate Office or the nearest Land-Grant University to connect with scientists, educators, and extension staff in your local area. 

METHODOLOGY

2010 county-level annual estimates of runoff avoided (gallons), CO2 equivalent absorbed  (tons), and air pollution reduced (pounds) were obtained for 242 locations using the U.S. Forest Service i-Tree County tool. Detailed information about the methodology can be found here. Estimates are not available for Alaska, Hawaii, or Puerto Rico. Local graphics highlight data for the county in which each city is located. For cities spread across multiple counties (Amarillo, Texas; Huntington, W.Va.; Joplin and Kansas City, Mo.; New York City, N.Y.; and Shreveport, La.), estimates for all counties were aggregated. County names can be found in the footnote of each local graphic.