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California is missing out on billions of gallons of stormwater each year, report finds

Hayley Smith, Los Angeles Times on

Published in News & Features

LOS ANGELES — For too long, California and other states have viewed stormwater as either a threat or an inconvenience — something to be whisked away from cities and communities as quickly as possible.

But as traditional sources of water face worsening strain from climate change, population growth, agriculture and other factors, those unused gallons of rainwater pouring across asphalt or down rain gutters are starting to be viewed as an untapped resource that can help close the widening gap between supply and demand.

In a report released Thursday, researchers with the Pacific Institute determined that every year, 59.5 million acre-feet of stormwater go uncaptured across the United States — or roughly 53 billion gallons per day. The amount is equivalent to 93% of the water withdrawals for municipal and industrial uses in 2015, the most recent year for which national data were available.

“The numbers are clear. It’s time to elevate the role of stormwater capture in the national water conversation,” said Bruk Berhanu, the report’s lead author and a senior researcher with the Pacific Institute, a California-based water-focused think-tank.

Of the 10 states with the most “untapped potential,” California ranks ninth with approximately 2.27 million acre-feet of urban area runoff each year. (An acre-foot is about 326,000 gallons — enough water to supply up to three homes for a year).

What’s more, Los Angeles represents the urban area with the greatest stormwater runoff potential in the West, ranking 19th in the country. The census-defined urban area includes L.A., Long Beach and Anaheim, and experiences approximately 490,000 acre-feet of runoff each year, or roughly 437 million gallons per day.


It would not be feasible or desirable to capture every drop of that missed water, as some stormwater is needed for environmental use, ecological health, recreation and other purposes, Berhanu said. Yet the sheer volume indicates that far more could be done, and that stormwater could become a significant supply alternative in communities across the country.

Texas was the state with the most untapped potential, 7.8 million acre-feet of urban area runoff each year. The analysis accounted for the size of each urban area as well as its historic annual rainfall, the researchers said.

The findings come at a critical moment. In California and many other parts of the world, traditional water sources — including underground aquifers and fresh water from rivers, streams and snowmelt — are becoming less reliable.

The Fifth National Climate Change Assessment found that the American Southwest can expect extended periods of reduced precipitation in the years ahead, which will be interrupted by bursts of extreme rainfall and flooding. The Colorado River — a water lifeline for 40 million people across the region — is projected to see flows reduced by as much as 30% by 2050.


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