During heavy rainfall, trees help reduce flooding and reduce pollutants in water flowing to streams and rivers (stormwater runoff). How do trees do this?
- Large leaf canopies catch and hold a large amount of water that will evaporate without ever reaching the ground. A tree canopy also slows water runoff. You’ve probably stood under the canopy of a tree and watched it rain for several minutes before ever getting wet. Slowing runoff reduces flooding.
- The deep, extensive roots of a tree increases the amount of water that penetrates the ground (infiltration). This also helps recharge groundwater. One study showed that an area with trees allowed infiltration of 10 inches of rain per hour, but a lawn area only absorbed 4 inches per hour.
- Trees pump water up from the soil to their leaves, for photosynthesis. A significant amount of pumped water evaporates from their leaves – around 80-100 gallons per day in summer for a large tree. Tree species used specifically for stormwater control, like the bald cypress, can pump up to 800 gallons per day.
- As they grown, trees take up a number of pollutants, including heavy metals, and store them in their wood. This reduces contaminants that would otherwise reach our rivers and drinking water sources.
- The root systems of trees help hold soil in place, reduces sediment that is a major aquatic pollutant in Tennessee.
Planting and maintaining trees in areas around parking lots and streets, where we often have issues with excess water during heavy rain, is a great solution that also provides cooling shade and improved property values.
References and more information:
PennState Extension. Video: How Do Trees Reduce Stormwater and Flooding?
U.S. Environmental Protection Agency Soak Up the Rain: Trees Help Reduce Runoff