Urban trees are widely celebrated for their important role in improving air quality, sequestering carbon, and reducing the urban heat island effect. However, one often overlooked benefit of a healthy tree canopy is the integral role it plays in stormwater management.
When precipitation cannot infiltrate the soil, it instead flows across the ground as stormwater runoff. This runoff flows rapidly over the surface, eroding topsoil and deteriorating stream channels while collecting pollutants such as oil, trash, fertilizers, and pesticides. These contaminants are eventually deposited into our local waterways, where they pollute water, fuel harmful algal blooms, clog navigation channels with sediment, and disrupt sensitive aquatic habitats. Research shows that urban trees can reduce these impacts by absorbing 15–27% of annual rainfall, reducing runoff and limiting erosion.
Traditional stormwater management has relied heavily on gray infrastructure in the form of drains and pipes that quickly convey runoff to treatment facilities. These systems are expensive to build and maintain and are increasingly strained by runoff from ever-expanding impervious surfaces. In response, many communities are adopting green infrastructure approaches that aim to manage stormwater closer to its source. Management practices such as green roofs, permeable pavement, bioswales, and rain gardens reduce impervious surface cover and promote infiltration by slowing and temporarily storing water on site rather than channeling it directly into traditional stormwater infrastructure.
Urban trees complement and expand the capacities of these green management practices by intervening even further upstream. In addition to improving infiltration and stabilizing soils, trees intercept a significant volume of rainfall before it reaches the ground. Depending on species and size, a single tree can temporarily store over 100 gallons of stormwater on its leaves and bark. Integrating urban tree canopies into stormwater planning can be a natural, cost-effective solution to reduce strain on traditional infrastructure and protect our sensitive waterways.
References:
Arbor Day Foundation. How Trees Can Retain Stormwater Runoff. Tree City USA Bulletin No. 55. https://www.arborday.org/tree-resources/how-trees-can-retain-stormwater-runoff .
Berland, A., Shiflett, S. A., Shuster, W. D., Garmestani, A. S., Goddard, H. C., Herrmann, D. L., & Hopton, M. E. (2017). The role of trees in urban stormwater management. Landscape and Urban Planning, 162, 167–177. https://doi.org/10.1016/j.landurbplan.2017.02.017.
Center for Urban Forest Research, Pacific Southwest Research Station. July 2002. Fact Sheet #4: Control Stormwater Runoff with Trees. USDA Forest Service. Davis, California. https://www.fs.usda.gov/psw/topics/urban_forestry/products/CUFR_182_UFfactsheet4.pdf.
Dowtin, A. L., Cregg, B. C., Nowak, D. J., & Levia, D. F. 2023. Towards optimized runoff reduction by urban tree cover: A review of key physical tree traits, site conditions, and management strategies. Landscape and Urban Planning, 239, 104849. https://doi.org/10.1016/j.landurbplan.2023.104849 .
Environmental Protection Agency. 2025. Soak Up the Rain: Trees Help Reduce Runoff. EPA. https://www.epa.gov/soakuptherain/soak-rain-trees-help-reduce-runoff .
Environmental Protection Agency. 2025. Urbanization and Stormwater Runoff. EPA. https://www.epa.gov/sourcewaterprotection/urbanization-and-stormwater-runoff.
MD Forest Service. Forests for Healthy Waters, Sustainable Communities Principles and the practices for using forests and trees in land planning. MD DNR. https://dnr.maryland.gov/forests/documents/forestsforhealthywaters.pdf .
U.S. Department of Agriculture, Forest Service. 2020. Urban forest systems and green stormwater infrastructure. FS–1146. Washington, DC. 23 p. https://www.fs.usda.gov/sites/default/files/fs_media/fs_document/Urban-Forest-Systems-GSI-FS-1146.pdf .
Photo Credit:
Photo by Adrian Pelletier on Pixnio. https://pixnio.com/media/detail-green-leaves-rain-raindrop-spring-time
