- Mature trees intercept rainfall in their crowns, reducing runoff and providing cleaner water. Stand under a full-leafed tree at the start of a rain storm. Look at the wet ground beyond the tree and observe how long the ground under the canopy stays dry.
- Computer simulations of deciduous trees in California’s Central Valley estimate that for every 1000 trees, rainwater runoff is reduced nearly 1 million gallons – a significant monetary value.
- Reduced runoff means that there is reduced flooding in the streets.
- A secondary effect of the reduced runoff is that dirt is not washed into lakes, rivers and the ocean, reducing sedimentation.
- Reduced runoff also means that heavy metals and other pollutants from roads, parking lots, and roofs are not carried into our water supply. This reduces the load on water treatment facilities.
The American Society of Landscape Architects has produce some informative animated videos on the benefits of proper landscaping for water management. Trees, particularly native trees, are a part of their water management plans.