How dynamically managing California's reservoirs could save more water Decades-old rules mean most reservoirs aren't allowed to fill up in the winter. A new approach using weather forecasts is helping some save more water to help with California's drought.

Heavy rain is still hitting California. A few reservoirs figured out how to capture more for drought

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MARY LOUISE KELLY, HOST:

Heavy rainfall is continuing to pummel California. While most residents were sheltering from the storms, a research team from the National Oceanic and Atmospheric Administration was flying right into one.

(SOUNDBITE OF ARCHIVED RECORDING)

UNIDENTIFIED PILOT #1: Power set. Air speed's alive.

KELLY: The NOAA Hurricane Hunters were on a mission to go into an atmospheric river. That's like a literal river of moisture in the sky, a storm that stretches hundreds of miles. From 45,000 feet up, the team released special instruments called dropsondes. They look like burritos with parachutes, and they collect data about the storm.

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UNIDENTIFIED PILOT #2: Three, two, one - mark - release sonde now.

KELLY: The flight can be a bumpy ride for the crew, but the info that they're gathering is helping improve storm forecasts, especially flood alerts. And it's not just about wet weather. These missions are helping California deal with dry conditions, too. NPR's Lauren Sommer is here to explain how. Hey there.

LAUREN SOMMER, BYLINE: Hi, Mary Louise.

KELLY: So this is the paradox, I guess, for California right now, that there's all this rain and yet the state's drought is ongoing. How are these winter storm forecasts helping with the drought side of things?

SOMMER: Yeah, that's exactly what California officials have been saying. The state is in a flood emergency and a drought emergency at the same time. And that has a lot of people asking, how can the state catch more of this flood water? How can more be stored to last through the dry season, you know, given how low reservoirs have been? And today, there's a rule that's working against that in some cases, which is that reservoirs aren't allowed to be full in the winter. They actually have to empty themselves out.

KELLY: Why? Would filling up the reservoirs would seem to be advantageous in a state that is so chronically dry?

SOMMER: Yeah, it would be. But reservoirs actually have another job in the winter, too, which is to catch the runoff from storms so that it doesn't flood cities and towns downstream. They can't do that if they're full because the dams could be easily overwhelmed. So most reservoirs have automatic rules that say, in late fall, they have to release a certain amount of water if they're too full.

KELLY: A certain amount - how much water are we talking?

SOMMER: Yeah, one example, there's a major reservoir outside of Sacramento, Calif., called Folsom Reservoir. The rule there said it could only be 60% full in the winter, at the most. And that means sometimes the reservoir would empty itself out when it didn't really need to because no major storms arrived. So now they're trying something else, which is to dynamically manage the reservoir using weather forecasts so the reservoir doesn't empty out preemptively. It only does if a big storm is on the way.

KELLY: OK. So it is the forecast that will determine what this reservoir does, which means the forecasts would need to be very accurate because public safety is on the line.

SOMMER: Yeah, exactly. And, you know, that's where those NOAA's storm reconnaissance flights are coming in. They're helping fine tune those forecasts even more. And this winter, really, is the first time Folsom Reservoir is kind of being managed this way, when there's this big stream of storms hitting. And when I spoke to the Bureau of Reclamation, which manages that reservoir, they said it's working well so far.

KELLY: I'm thinking through the possibilities here. With all the storms happening right now, all the rain coming, might managing reservoirs in this way, this more dynamic way, might that help California with its drought that we're expecting to continue in the coming year?

SOMMER: It could, yeah. You know, especially if there's a repeat of last year, where the storms just kind of dried up in January. And as the climate gets hotter, you know, this could be a pattern that California sees more of. That's what Marty Ralph, who studies reservoirs at UC San Diego's Scripps Institution of Oceanography, told me.

MARTY RALPH: Longer droughts, deeper droughts and bigger storms between them. So we need to prepare. There's a lot at stake. And these are methods that could really help us with climate adaptation.

KELLY: Lauren, is this something that other states, other reservoirs across the West are looking at?

SOMMER: Yeah. Right now, it's just two reservoirs working this way in California. A handful of others are studying it. And I spoke to David Raff, chief engineer for the federal Bureau of Reclamation, about the possibilities beyond that.

DAVID RAFF: The climate is changing, hydrology is changing, weather patterns are changing. In addition to that, the demand for water is increasing in the western United States. When you put those things together, there is a significant interest to optimize reservoir operations in all of our reservoirs.

SOMMER: You know, most of our water infrastructure is designed to fit the climate of the past, and that's, obviously, not a good fit going forward. But there's a lot more real-time data out there today, you know, to help dynamically manage these systems as things are changing, you know, if water managers choose to use it.

KELLY: NPR's Lauren Sommer from our climate desk. Thank you so much, Lauren.

SOMMER: Thanks.

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