Stormwater Trees

How Trees Help Manage Water in Your Lawn and Landscape

By Melinda Myers - horticulturist and gardening expert

• Interception: How Trees Intercept Rainfall
  • ​​​​​​​When rain lands on a tree it collects on the leaves, branches and trunk. This water either evaporates back into the atmosphere or is absorbed by the tree. This means less water reaches the ground helping to reduce the amount of water entering our storm sewers.
    • One study found a typical medium-sized tree can intercept as much as 2380 gallons of rainfall each year

• Transpiration: How Trees Absorb Water 

  • Trees absorb water from the soil that travels from the roots, through the tree and is eventually released in a gaseous form through small pores in the leaves. The rate of transpiration is impacted by many factors such as rainfall, humidity, wind speed, temperature and soil type.

    • Research has found that a healthy 100 foot-tall tree with 200,000 leaves can absorb 11,000 gallons of water from the soil and release it into the air as oxygen and water vapor in a single growing season.  

• Infiltration: How Tree Roots Help Soil

  • Tree roots and organic matter in the soil create easier access for water to move into the soil. This reduces the amount of rainfall that ends up running off the soil surface and potentially into nearby waterways and storm sewers.​​​​​​​ Mature trees have the greatest impact.  As tree roots grow they open entryways for the water. As the old roots die they add organic matter to the soil.​​​​​​​​​​​​​​

Milwaukee Stormwater Tree Project

With our climate changing, Milwaukee can expect more intense rain, bigger storms, and changes in temperature. With intense rain, all the house, street, and sidewalk runoff can overwhelm our sewer system. Stormwater trees are part of Milwaukee Metropolitan Sewerage District’s (MMSD) green infrastructure solutions to managing rainwater and improving water quality in our urban waterways. 

In 2020 and 2021, over 400 trees were planted in a 2-mile square area on the northwest side of Milwaukee with an additional 100 trees anticipated to be planted in 2021 as part of the “Improving Our Neighborhood One Tree At A Time” project. These trees can soak up over 255,540 gallons of stormwater in any given storm and help improve air quality by removing 4.58 million pounds of carbon dioxide every year (the gas that causes climate change). 

The “Improving Our Neighborhood One Tree At A Time” program increases community resilience through improved tree canopies. This program goes beyond a traditional planting program and targets both public and private properties in a socially and economically vulnerable community (85% minorities with 33% of residents living at or below the federal poverty line).

This program gave neighbors the ability to drive decisions on community investments. Through robust bilateral communication, neighbors learned the importance of trees, the impact of climate change on our region, and used their voices to shape their neighborhood.  This program directly engaged over 300 residents in workshops, tree hikes, and community meetings. The residents decided what trees to plant, what educational information should accompany the new trees in public spaces, and committed to individual behavior changes to improve our waterways.

To support individual behavior change, residents that participated in the program through events and workshops were able to receive a free tree and/or rain barrel for their home. 60 rain barrels and 49 trees were given away to neighbors.

The “Improving Our Neighborhood One Tree At A Time” project received a National Environmental Achievement Award from the National Association of Clean Water Agencies, which recognizes public agencies for their outstanding efforts under the Operations and Environmental Performance category. The project also won an International Gold Leaf Award through the Wisconsin Arborist Association.

Partnering with MMSD, was the City of Milwaukee Forestry Division, Milwaukee Plays, Housing Authority of the City of Milwaukee, Milwaukee's Choice Neighborhood Initiative, and Havenswoods Neighborhood Partnership.  This project was funded in part by the Great Lakes Restoration Initiative and U.S. Forest Service. For more information about this project please contact us.