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If the models hold true, L.A. is in store for a double whammy of floods and drinking water shortages.

Around the country, cities are doing their best to plan ahead for the impacts of climate change. In New York, more intense storms could put parts of the Financial District underwater and wreck havoc on roadways and subway lines. In New Orleans, rising sea levels may submerge wetlands altogether, increasing the city’s vulnerability to hurricanes. And in the Southwest, metro areas are expected to have a harder time supplying their populations with water.

But few cities are facing the serious environmental double whammy that’s most likely in store for Los Angeles. Not only do scientists predict that rising sea levels will increase the likelihood of coastal flooding there, but also that rising temperatures will threaten the snow pack in the Sierra Nevada mountains, which provides about a third of the drinking water used by the L.A. Department of Water and Power, the nation’s largest municipal utility.

L.A. still gets nearly 90 percent of its drinking water from out-of-town resources, just as it has for more than a century. But the Sierra Nevada snowpack could shrink by as much as 90 percent by 2100, experts say. Runoff already peaks 10 to 15 days earlier today than it did 50 years ago, according to a 2008 Purdue University study

Meanwhile, aquifers along the coast of Los Angeles County are already experiencing "seawater intrusion," according to the National Resources Defense Council, which last year called out L.A. officials for lagging behind other big cities in planning for such climate change-related effects. The group warns that a 55-inch sea level rise would double the number of toxic waste sites, power plants and other critical infrastructure situated inside L.A. County’s 100-year flood zones.

“New York, Chicago, and Seattle are more of a gold standard in terms of looking at how climate change will impact them. But at least L.A. is looking at it,” says Michelle Mehta, an attorney with NRDC.

L.A. Mayor Antonio Villaraigosa issued the city’s “Green L.A.” climate change mitigation plan in 2007. The city’s water department, meanwhile, commissioned consulting firm Tetra Tech, Inc. to examine its water supply concerns. Among the more novel ideas Tetra Tech came up with in its 2011 report: Building underground reservoirs along the 340-mile Los Angeles Aqueduct.

In the meantime, the water department is looking closer to home.

“We want to cut our water imports in half by 2035 and make a major shift to more reliable local supplies,” by cleaning up groundwater pollution in the San Fernando Basin, recharging other groundwater supplies, and treating and recycling more stormwater and raw sewage, says Jim McDaniel, LADWP's senior assistant general manager for water.

The department has test wells to study the contamination plume in the San Fernando Basin, a legacy of World War II-era manufacturing. It’ll be two or three years before construction could begin at a cost of upwards of $700 million, McDaniel says. But the new plants would allow it to reopen San Fernando wells sidelined by pollution and expand stormwater and ramp up grey water recycling, as well.

“There’s always going to be a need for imported water,” McDaniel says. “But the more we can depend on our local resources, the better off we’ll be.”

Photo credit: Micimakin/Shutterstock

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