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This vegetated depression, or swale, helps storm water infiltrate into the earth rather than running rapidly off sidewalks and streets. While helping prevent damaging floods, bioswales can recharge local groundwater, beautify urban landscapes, and purify water all at the same time. This particular swale is in Seattle, but more may soon grace the streets of Los Angeles. Photo courtesy of US Environmental Protection Agency

A Watershed Moment for Los Angeles

November 14, 2014

The timing might seem odd, even self-destructive.

Last month, in the midst of one of the most severe droughts in California’s historical record, Los Angeles Mayor Eric Garcetti issued an executive order calling for his southern California city to cut its water imports by half within a decade.

Water transferred hundreds of miles from northern California and the Colorado River currently accounts for about 80 percent of LA’s water use, so the goal is ambitious, to say the least.

It’s also a historic turn-around. Ever since the early 20th century, when Los Angeles diverted water from the Owen’s Valley a couple hundred miles to the East – a deal made famous by the classic Roman Polanski film, Chinatown – Los Angeles has done what just about every growing western city has done: reach further and further out for more water as demands outpace supplies.

But with his bold new directive, Garcetti is writing a new script for LA’s water future.

Instead of relying on distant supplies brought in by big engineering projects, he’s banking on the idea that local supplies can meet most of the city’s water needs if they are used more efficiently and managed with more ingenuity.

Ultimately it’s about smarter water management and greater resiliency. Transferring water long distances, and especially over mountain ranges, is energy-intensive and costly. Moreover, those distant supplies are becoming less reliable. Most of LA’s imported water originates as snow in the Sierra Nevada and Colorado Rockies, and climate scientists expect those snowpacks to diminish in the coming decades.

Due to the ongoing drought, the Metropolitan Water District, which supplies Los Angeles with most of its imported water, expects to curtail supplies during the coming year.

Garcetti’s directive puts forth two other goals, as well: to reduce water use per person by 20 percent within three years, and to create an “integrated water strategy” that boosts local water supplies and improves water security. Achieving these goals is critical to meeting the water-import reduction target.

In some ways, LA’s past conservation successes make achieving these goals more difficult. Thanks to tried-and-true conservation efforts, the city’s water use today is back to where it was 40 years ago, when a million fewer people lived there.

But the Mayor’s directive acknowledges an important truth: that the city has barely scratched the surface of water conservation’s potential to meet future water needs cost-effectively and sustainably.

For one, Angelenos can reap substantial water savings by choosing more sensible, climate-appropriate vegetation. Landscape irrigation accounts for more than half of LA’s residential water use.

The mayor’s plan calls for increasing rebates for residential turf removal, giving property owners an incentive to switch from thirsty lawns to drought-tolerant vegetation. It also calls for 85% of public golf course acreage to be irrigated with recycled water by 2017, saving higher-quality potable water for drinking, showering and other household uses.

To increase local supplies, Los Angeles will look toward rainwater harvesting, stormwater capture and other techniques that prevent precipitation from running off impervious streets and pavement instead of recharging groundwater, increasing soil moisture, or being stored for other uses. A one-inch rain event in Los Angeles County can generate more than 10 billion gallons of stormwater runoff – most of which will flow, along with the urban trash and pollution it is carrying, into the Pacific Ocean.

Gardens on rooftops, vegetated swales in parking lots, and other types of “green infrastructure” help turn storm water into an asset rather than a problem.

A study of urbanized southern California and the San Francisco Bay Area, conducted by the Natural Resources Development Council and the University of California at Santa Barbara, found that rooftop rainwater capture combined with increased stormwater infiltration to recharge groundwater could increase water supplies by up to 405,000 acre-feet (132 billion gallons) within two decades.

There’s no big silver bullet in the Mayor’s plan. It’s a portfolio of actions to build water security, self-reliance and long-term sustainability. It’s also the look of urban water management in the 21st century.

Much of the world will be watching.

Originally published at National Geographic Newswatch.