Rains and storms have been sweeping California for the last couple of months, making 2017 a big wet year. While this is so great, relieving the state’s historic, 5-year drought, and lifting half of the state out of drought, now we face another issue opposite the drought: stormwater runoff, and in some places, flood and mudslide. Due to mudslide, some free ways in North Cal have to be closed. How can we better manage stormwater and reduce the hazard? One of the key answers lies in something we see all the time – trees.
For their critical function of photosynthesis and other functions, trees need a lot of water. They take water from soil, finish the processes, and evaporate it into air. Each tree is like a sponge that absorbs away a large amount of rainwater that sinks in soil. In addition, the branches and leaves of trees, like arms and hands, can catch and absorb a big amount of raindrops falling from sky, reducing that falling on ground. As trees draw away so much rain water, they reduce runoff.
The canopies of trees can slow down raindrops falling through them significantly, reduce the force they hit the ground; On the ground, trees block and slow the current of stormwater, reducing its force to carry soil; underground, the roots of trees bind soil tightly so they are not as easily washed away. All together, tress lessen the impact of rainfall for soil, effectively reduce erosion and mudslide.
The root systems of trees break up the soil, create space for air and water, support the growth of living organisms and worms; the fallen leaves, and the waste of animals live in the trees further add to the organic matters deposited onto the soil. Together they improve the quality of soil, and its capacity to hold water. According to USDA, “Each 1 percent increase in soil organic matter helps soil hold 20,000 gallons more water per acre.” When the heavy rains come, healthy soil helped created by trees can absorb much more water than barren soil, reduce runoff and its hazard.
From the long course that stormwater flows over, especially in cities, it usually carry a certain amount of pollutants, such as metals, chemicals, etc. When trees draw water from soil for its photosynthesis and other functions, they also draw pollutants with it. After the processes, these pollutants are transformed into less harmful substances, and delivered to all parts of trees. Trees are natural purifiers that filter out the harmful substances, making water and environment for us cleaner and safer.
Trees have always been an important part of water efficient gardens. In dry times, along with native and drought tolerant plants, trees can beautify the landscape, cool down the area, reduce demand for water, improve soil quality and enhance overall capability of water conservation. In rainy season, as trees are such great stormwater managers, they can help the community reduce runoff and loss of soil. Quite a few popular trees, i.e., Crape Myrtle, Fig, Avocado, Pomegranate, etc, which qualify for Santa Clara Water District’s Landscape Conversion Rebates, are good choices to be included in a water efficient garden. With such a tree in your garden, not only will you enjoy its shade and fruits, but also that great feeling that they are strong helpers in rainy season as well as dry.