To Fight the Drought, L.A. Needs a Rain Revolution

To Fight the Drought, L.A. Needs a Rain Revolution

Dry, thirsty Los Angeles is trying to capture more storm water, restore a river and learn from the past

By Cynthia Barnett in the Wall Street Journal

A fast-moving Pacific storm swept across northern California and down the coast to Los Angeles last week, bringing a rare rain delay to Dodger Stadium in the middle of the season opener—and some relief to the vast urban population suffering from the state’s severe drought.

Unlike thirsty cities of the past—such as ancient Carthage in Tunisia, which meticulously captured every drop of its scant rain—metro Los Angeles wasted much of the .36 inch that fell on April 7. Flowing across miles of highways, rooftops and parking lots, the liquid manna made its way to L.A.’s ubiquitous, concrete storm gutters, which then rushed it away to the Pacific Ocean.

This was entirely by design. Over the course of the 20th century, city leaders worked to banish rainfall to protect Angelenos from a very different sort of disaster. Before engineers built mammoth flood-control dams and turned the sinewy L.A. River into a 54-mile storm drain, fierce floods had routinely washed away homes and killed residents of the fast-growing city.

Large-scale flood control saved lives, but it also carried two unhappy and unintended consequences. In L.A., as elsewhere, storm water running off filthy streets and car parks has become a major source of pollution, fouling beaches, bays and rivers. In addition, rain captured and redirected this way couldn’t be used to quench thirst in dry times.

Today, an estimated 85% of Los Angeles is urbanized—65% of it covered in asphalt and concrete. This keeps rainfall from seeping back into the ground to top off aquifers and makes it unavailable for drinking water. The Arid Lands Institute at Woodbury University in Burbank, Calif., estimates that L.A.’s massive flood-control system shunts some 520,000 acre-feet of rainfall to the Pacific Ocean each year—enough to supply water to perhaps a half million families.

Fortunately, L.A. has made some progress in restoring the balance. The city that has long represented concrete sprawl at its most dystopian is changing its relationship with rain. From individual backyards to college campuses, many Angelenos are installing cisterns and taking sledgehammers to sealed surfaces so that floodwaters can drain more naturally and rain can return to the aquifers.

The city was already at work on the long-term dream of restoring the L.A. River, but this drought has made clear that won’t be enough. “The work on the river is incomplete without also working on the water that falls in the foothills, in the low-density residential fringes, in the high-density core, in the commercial and industrial areas, in the airport,” says Hadley Arnold, executive director of the Arid Lands Institute. “The idea is to see water not in a 54-mile line but in a field.”

That is a massive undertaking. Aiming to stem both pollution and the city’s reliance on imported water from the Sierra Nevada mountains to the north and the Colorado River—high-cost, high-energy supplies increasingly limited by drought—the Los Angeles Department of Water and Power has launched a major retrofit of its storm-water system. Engineer Mark Hanna, a member of the project’s technical team, estimates that L.A. could source a third of its water locally—up from a tenth today. The plan includes massive “spreading grounds” (gravel-lined pits that allow rain to percolate back to aquifers) on publicly owned lands that absorb the most rain; smaller neighborhood infiltration basins; and incentives for filtration on private property. “When you think of the scale, we can do 1,000 neighborhood infiltration basins, we can do 100,000 rain gardens,” Mr. Hanna says. “It’s an enormous amount of water saved.”

Another source of water: Using less of it. L.A.’s water use per capita had been in steady decline for decades, despite its population growth, but a new study from the UCLA Institute of the Environment and Sustainability shows that demand has ticked up since 2011. Angelenos use about 130 gallons of water a person every day. Mayor Eric Garcetti released a new plan last week that aims to cut that to 105 gallons a day by 2017.

Meanwhile, Ms. Arnold and her fellow green architects and engineers see L.A. as the great Western test for what they call “drylands design.” They hope to make rain a centerpiece of architecture, building codes and zoning laws. They are looking to successful strategies of the past, from the sharing model of 19th-century Mormon irrigation districts in Utah to the extensive cistern works of ancient Carthage. And they are developing digital tools to help arid communities design and build in ways that capture, filter and distribute rainfall.

The big question: What if it doesn’t rain?

Even in severe drought, Mr. Hanna says, “it does rain, and it will rain. And when it does, unless things go really strange on us, the rain will tend to fall in the mountains and gather in the canyons and accumulate in the low spots.” However much comes down, he stresses, “We need to capture every drop.”

— Ms. Barnett is the author of “Rain: A Natural and Cultural History,” to be published Tuesday by Crown.