STEVE INSKEEP, HOST:
And let's go next to California where heavy rains have been testing the Oroville Dam, and, as it turns out, many other levees and dams. From member station KQED, Lauren Sommer reports.
LAUREN SOMMER, BYLINE: About 60 feet of levee has been eaten away, just gone here in the Sacramento-San Joaquin Delta. A huge crane is dumping rocks in that gash to try to stop the river from breaking through. Steve Mello is watching every rock load, anxiously gnawing on his cigar.
STEVE MELLO: Every hour, we work we're safer. We're not out of the woods yet by a long shot.
SOMMER: Mello is a farmer here on Tyler Island in the delta, about two hours from San Francisco. The farms and homes nearby would be under water without this levee. And Mello watched it crumble in only 15 minutes.
MELLO: We went from, oh, criminy (ph) sakes, we got another minor slip to, oh, my God, call for a mandatory evacuation.
SOMMER: All eyes in California have been on Oroville Dam where a broken spillway forced major evacuations. But flooding has been happening all over. Winter storms have stressed thousands of miles of rivers and levees. Even as we're talking, the crew suddenly stops working and runs to check out another problem.
Does it look bad?
MELLO: Well, I heard somebody say something about slip.
SOMMER: This time, Mello got lucky. Days later, the levee repairs are still holding. And like Mello, most Californians are still in shock that after five years of too little water, now the problem is too much.
NOAH DIFFENBAUGH: This shouldn't be a surprise.
SOMMER: Noah Diffenbaugh is a climate scientist at Stanford University.
DIFFENBAUGH: It's actually exactly what has been predicted by scientists for, you know, at least 30 years.
SOMMER: Diffenbaugh says California is likely to see more extreme flooding with climate change. And the reason is pretty simple. If it's warmer, storms produce more rain instead of snow. But that's not what California's water system was designed for a century ago.
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UNIDENTIFIED MAN: The key that unlocks Earth's living bounty is water.
SOMMER: It was built in large part around the snowpack in the Sierra Nevada.
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UNIDENTIFIED MAN: In early spring, the warming sun begins its work of melting the great snow fields and ice-choked valleys.
SOMMER: California's flood system can handle that slow melt, but not a huge amount of rain all at once Diffenbaugh says.
DIFFENBAUGH: Our water system was really built in an old climate. It's a climate that is no longer the climate of California.
SOMMER: What can California do about this? Some are calling for more dams to be built, but even if dams are big enough to handle flood events, the channels downstream may not be able to, says Jay Lund. He directs the Center for Watershed Sciences at the University of California, Davis.
JAY LUND: This flood here has really tested us. We found that we have quite a bit of levees to work on still.
SOMMER: And dams aren't the only place to store all that runoff, he says.
LUND: The biggest source of water storage in California is groundwater, and it always will be.
SOMMER: California is experimenting with spreading floodwater onto fields where it can seep into the groundwater. That groundwater needs recharging. After being heavily used during the drought, but there's still a long way to go if the state is going to catch up to the climate it has now. For NPR News, I'm Lauren Sommer in San Francisco.
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