Pacific Southwest Research Station

Urban Ecosystems and Processes

WATER

Urban forests reduce stormwater runoff, thereby slowing the flow of pollutants into streams, lakes and oceans. Tree crowns intercept rainfall, thereby reducing the amount of runoff. Tree roots make the ground more porous. As a result, water runoff from storms can be more readily absorbed by soil. In most cases, models of hydrological processes in forests cannot be applied to cities. Forest stands typically consist of fewer species than found in urban forests and trees in cities rarely occur in large groups of trees like those in large tracts of forested land. For this reason, scientists have developed rainfall interception models for single open-grown trees and for trees in urban watersheds. The references below contain additional information on the influence of urban forests on stormwater runoff.

References

1. Is All Your Rain Going Down the Drain?
2. How Trees Can Retain Stormwater Runoff
3. Performance of Engineered Soil and Trees in a Parking Lot Bioswale
4. Rainfall Interception of Three Trees in Oakland, California
5. Cooperative Research in Urban Hydrology
6. EcoSMART - WaterWise
7. Measuring and Modeling Hydrologic Processes at the Residential and Watershed Scales
8. Miscellaneous Water Literature
9. Modeling Urban Tree Rainfall Interception
10. Rainfall interception by Santa Monica's municipal urban forest