MADELEINE BRAND, host:
This is DAY TO DAY. I'm Madeleine Brand.
ALEX CHADWICK, host:
I'm Alex Chadwick.
Coming up, a conversation with a politician for whom politics truly is a matter of life and death - a member of the Afghan parliament.
BRAND: First, the storms that battered California over the weekend dropped several feet of much-needed snow in the Sierra Nevada mountains. When that snow melts this coming spring, it will help bolster the strapped water supply in the northern part of the state, the Sacramento-San Joaquin Delta. That's the hub of a complicated water system that supplies much of the state.
CHADWICK: But if climate change predictions come true, the delta's role may change.
From member station KQED, here's reporter Tamara Keith.
TAMARA KEITH: The Sacramento-San Joaquin Delta is where two major rivers and the San Francisco Bay come together. It used to be a wide-open marsh, where the balance of salt water and fresh water fluctuated with the tides.
Then a century ago, 1,000 miles of levees were built, creating dozens of delta islands and draining the marsh. Now there's a system of channels and pumps designed to carefully manage all the precious water that moves in and out of the delta.
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KEITH: We're on Sherman Island, which is one of the largest islands in the delta, and it's sort of about the edge - is at the confluence of the Sacramento River and the bay, where the salt water meets fresh water. This is California's water supply.
Professor JEFF MOUNT (University of California Davis): You bet. This is it. This comes down - it comes down to Sacramento here, turns left as it gets out towards San Francisco Bay, and is sucked back up to the pumps and exported off to four million people in the Bay Area, three million acres of agriculture in the San Joaquin Valley, and 21 million people in Southern California.
KEITH: That's U.C. Davis Professor Jeff Mount.
Prof. MOUNT: Notorious big mouth and Dr. Doom.
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KEITH: Why doom? Because Mount says climate change is conspiring against the fragile balance at work here in the Delta. In order to serve millions of Californians, the salty water of the San Francisco Bay must be kept away from the pumps that bring fresh water to cities and farms. It requires constant management and enough fresh water at all times to push the salt water back.
Prof. MOUNT: Climate change is driving the salt inward. Under climate change in the future, where we're sitting now, which is now fresh because of heroic efforts that were doing in managing water supply, it will inevitably be salty in the future.
KEITH: Mount heads an independent board of California scientists advising the state. They're projecting that sea level could rise by a foot by the year 2050 and three feet or more by the end of the century. That means trouble for the levees, rock and dirt mounts that keep the water in its place. Here's how Mount describes them.
Prof. MOUNT: Fragile, grubby levees which are in terrible shape.
KEITH: Mount says there are two types of levees, those that have failed and those that will fail.
Here on Sherman Island, wind-driven waves lap up against a rocky levee. During a typical storm with extreme high tides, there's about a foot between those waves and the top of the levee.
Prof. MOUNT: It's a game of inches out here. I mean, you're just sort of clinging to the edge here and with very little margin for error. Regrettably, the sea level is rising. So that's going to go over the tops of the levees much more often in the future.
KEITH: And to make matters worse, delta islands lose about an inch of elevation a year, as soil is oxidized and blown away. That's a problem because, as Mount puts it, nature abhors a vacuum.
Prof. MOUNT: We may be as much as 15 feet below sea level right here. And just on the other side of this levee is water that's at or above sea level. The tide's rising right now, and it's trying real hard to get in here. And it's just that crummy little levee which is keeping it from getting in here.
KEITH: Mount and most delta experts agree, the current situation in the delta isn't sustainable. Eventually, that fragile balance of salt and fresh water will shift in favor of salt.
Prof. MOUNT: It's going to do it one of two ways. It's going to do it gradually - a sea level rise and changes in inflows - or it's going to do it suddenly through a collapse of the levees.
KEITH: And if there's a major levee collapse, he says water will rush in so quickly it will suck salty water out of the bay and into the delta. Mount calls it the big gulp.
Prof. MOUNT: Just the noise of the water rushing into this island, and it sounded like a waterfall as this rushes in and scours this hole in the ground as the water rushes in, and hurling pieces of soil way out onto the island. I mean, the power of these levee breaks is immense. It's unimaginable, and there's nothing you can do about it.
KEITH: And that must be why they call him Dr. Doom. California's political leaders are now debating alternative plumbing scenarios for the state's water supply.
For NPR News, I'm Tamara Keith in Sacramento.
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