Super El Niño Brewing? How Planting Trees Can Help!

You may have seen the headlines. Water temperatures in the equatorial Pacific Ocean are among the highest ever recorded, leading weather forecasters and climate scientists to predict a super El Niño phenomenon in California. The El Niño pattern usually means wet, rainy winters for California, and some experts are saying we aren't prepared for this year's severe storms.

At Friends of the Urban Forest, we're always planning (and planting!) ahead. We know that planting more street trees will help San Francisco prepare for extreme storms. Here's how:

Tree Basins Soak Up Water

Flooding is a major concern for cities when intense rain hits. Here in San Francisco, we've seen our combined storm sewer system become overwhelmed and backed up during heavy rains, flooding roadways and neighborhoods. One of the best ways to limit flooding is to prevent storm water from entering the sewer system in the first place. Every time we plant a new street tree where one didn't exist before, we cut and remove concrete, which reduces the amount of impermeable surface area on that street. Tree basins allow rainwater to soak into the ground rather than run directly into the storm drain.

Tree Leaves Slow Rain

Trees' leaves also help to slow rain from reaching storm sewers. Evergreen species help capture and slow raindrops as they fall. Think about the leaves of a magnolia tree in a rainstorm. Water is slowed from reaching the ground by the broad leaves, and some of it never makes it to the ground at all. Leaves and bark retain water—in fact, a single mature tree can store up to 100 gallons of water!

Trees Filter Storm Water Pollutants

San Francisco faces an additional challenge when it comes to heavy rainfall. Our combined storm sewer system handles both storm water and waste water from homes and businesses. When it becomes overwhelmed by heavy volumes of rain, untreated water is expelled into the Bay and ocean, including waste and sewage, which is harmful for our marine ecosystems. Trees filter pollutants from storm water and ensure that less makes it into the storm sewer in the first place.

Not only do trees help cool our neighborhoods and clean our air, they help us prepare for extreme storms and heavy rains. The trees we plant today will help reduce flood risks on San Francisco's streets and protect our fragile marine ecosystems. Help us prepare for a stormy winter by being a tree planting volunteer!