Climate Change Is Threatening The U.S. West's Water Supply : Short Wave The past year has been the driest or second driest in most Southwestern U.S. states since record-keeping began in 1895. Climate Correspondent Lauren Sommer reports that farms and cities have begun imposing water restrictions, but the water supply will shrink no matter what the weather brings. The supply spans tens of millions of people and the farmland that produces most of the country's fruits and vegetables. As a result, the people who manage the West's complex water systems are realizing that with climate change, they can no longer rely on the past to predict the future.

Read more of Lauren's reporting.

Email us at shortwave@npr.org.

Climate Change Is Threatening The U.S. West's Water Supply

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MADDE SOFIA, HOST:

You're listening to SHORT WAVE from NPR.

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EMILY KWONG, HOST:

Hey, everyone, Emily Kwong here with NPR climate correspondent Lauren Sommer. Hey, Lauren.

LAUREN SOMMER, BYLINE: Hey there.

KWONG: Hey. Hey. So summer technically just started, but it seems like the drought in the western U.S. is already really extreme.

SOMMER: Oh, yeah. Yeah. There are some scary numbers, I'm sorry to say. Here I go. Almost half the population of the country is facing dry conditions. Seventy percent of the West is in severe drought already. Several states like California and Arizona had their driest year since record keeping began in 1895. Wildfire risk is really high. I could keep going here.

KWONG: This is very, very worrying, everything you're saying, especially when you put it in a big list like that.

SOMMER: Yeah, it really is. And as you might imagine, it's already leading to some difficult conversations.

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TED COOKE: Today, we will provide an update on the current status of the Colorado River.

SOMMER: So the Colorado River is a key water source for seven states, you know, around 40 million people. Ted Cooke is a water manager in Arizona, and he and his colleagues held a meeting in late April that everyone had hoped to avoid.

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COOKE: The reason we're meeting today is that Lake Mead is 38% full.

SOMMER: Lake Mead is the largest reservoir on the Colorado River and, you know, in the country, for that matter. It's just outside of Las Vegas, and it's formed by the Hoover Dam.

KWONG: Yeah, Lauren, I have been to the Hoover Dam.

SOMMER: Oh.

KWONG: My family and I drove over the Hoover Dam when you could still do that when I was 14. And what I remember is it's this, like, precipitously tall, massive concrete dam in a steep rock canyon. And when you look down at it, it's kind of dizzying, it's so high.

SOMMER: Yeah. Yeah. And so back then, you probably saw, like, a decent amount of water in the reservoir.

KWONG: Definitely.

SOMMER: Yeah. So since you've been there, the reservoir has dropped by a lot. Since 2000, it's fallen by a 140 feet.

KWONG: Wow.

SOMMER: So now what you see when you look out is this white bathtub ring on the rocks around the reservoir, which kind of shows where the water used to be. And just this month, it fell to its lowest point since it was first filled in the 1930s.

KWONG: That is shocking. And does that mean people have to start cutting back on their water use?

SOMMER: Yeah. And this summer, you know, we're expecting the first ever official shortage to be declared on the river, which basically means mandatory cutbacks for states like Arizona, which is why they called that meeting. Ted Cooke is expecting a 30% cut. He called it...

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COOKE: So this is a painful reduction.

SOMMER: ...Painful.

KWONG: So, Lauren, who is this water cut most going to affect? Like, who gets less water in these seven states?

SOMMER: It will mostly be farmers, although they're getting some water from other sources to kind of make up for the shortfall. But here's the thing...

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COOKE: It is important to note that this is a day we knew would come at some point, meaning tier-one shortage.

SOMMER: The writing has been on the wall for a long time in the West. I mean, it's been dry. There's been a 20-year drought, but hotter temperatures are shrinking the water supply, too. So even if it rains again next year, supplies are still expected to decline for decades to come, and that will affect millions of people.

KWONG: So today on the show, a big moment in the West, how climate change is threatening the water supply and how, even if it rains, the threat will continue long into the future. This is SHORT WAVE, the daily science podcast from NPR.

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KWONG: OK, Lauren Sommer, the drought is a big story this summer, but I don't have a great sense of whose water is most at risk here. And you live on the West Coast. So who is most affected by this?

SOMMER: OK, yeah. So a good way to answer this is with a question. Have you eaten a salad during the wintertime?

KWONG: I have. I know the importance of leafy greens.

SOMMER: OK, well, then you have tasted Colorado River water. Yeah. During the winter, the vast majority of lettuce that you find almost anywhere in the country is grown in California or Arizona. And it's kind of the same if you eat an almond or a walnut or a pistachio or lots of kinds of fruit that was grown in California with water from another important source, which is the mountain snowpack in the Sierra Nevada. So both are being hit by this drought.

KWONG: So this drought has ripple effects that go far beyond the West itself.

SOMMER: Yeah, and it's directly affecting cities from Denver all the way to Los Angeles because the southwest is a pretty arid region. So almost everything you see there, whether it's cities or houses or farms, it only exists because of this huge system that moves water around.

KWONG: But droughts in the U.S. aren't unusual, right? I mean, they're something that people know is coming that could happen at some point.

SOMMER: This is a good moment for some time traveling. Cue the filmstrip, please.

KWONG: Oh, OK. Here we go.

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UNIDENTIFIED PERSON: Stained with the soil of five states, the river cuts deep into the desert.

SOMMER: So in the early 1900s, Western cities knew that they needed a water source to grow.

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UNIDENTIFIED PERSON: Farmers and ranchers in Colorado, Wyoming, Utah and New Mexico wait for irrigation projects.

SOMMER: People started planning huge projects, you know, dams to catch the water, canals to carry it hundreds of miles. And with seven states wanting that water, they had to find a way to share it. So in 1922, the states met, and in some very tense negotiations, they divided up the water.

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UNIDENTIFIED PERSON: A Colorado River felt the reins of man's control.

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KWONG: That is some serious, like, people dominating nature energy right there.

SOMMER: Yeah, yeah. And as you might imagine, it didn't necessarily work out. When the states met, they needed to know how much water there was to divide up. So they looked at the previous 20 years of flows down the Colorado River. And it turns out that period of time was unusually rainy and wet.

KWONG: So they were thinking that the future would be like the past, right? Because if it was really rainy then, did that give them the wrong impression, that it told them that there was more water than there actually is?

SOMMER: Yeah, exactly. I mean, it was just basically the wrong baseline to pick.

KWONG: Oh, no.

SOMMER: And there were people that warned them at the time. Since then, the Colorado River has just had less water on average. I talked to Park Williams, an associate professor of hydroclimatology at the University of California, Los Angeles, about what that means.

PARK WILLIAMS: The Colorado River is overallocated. Add up the amount of water that all the states in the West are promised, that's more water than we actually see flowing down the river on average.

SOMMER: And this gets to the fundamental problem. You know, most of us accept that the future will be different from the past. But water systems were designed for a stationary climate, as scientists call it. They were built for certainty, the idea that whatever happened in the past will just keep happening the same way.

KWONG: Which is not the reality at all.

SOMMER: No.

KWONG: So you're saying these water systems were designed a century ago and now human-caused climate change is really shifting things.

SOMMER: Yeah, that's it, you know. And hotter temperatures just basically make it less likely that any raindrop or snowflake will make it to a reservoir. And that's because, first, when it's hotter, there's just more evaporation. Plants and soils lose more water into the air, so less is running off into rivers and streams. And then second, dry soils are kind of like a sponge. They soak up rainfall, and it takes more water to fill them up before that water runs off. So that also reduces how much makes it into reservoirs.

KWONG: So, Lauren, are you saying that the water supply is being reduced all the time because of climate change anyway, whether there's a drought that year or not?

SOMMER: Yeah, exactly. So even if it rains a lot, the runoff is still lower. And then when there's a drought, which is, you know, a normal occurrence in the West, it makes it even worse, according to Park.

WILLIAMS: Over the last 22 years or so, there's been quite a bit of bad luck because precipitation totals have on average been low, but the effects of those have been really amplified. The effect of that bad luck has been really amplified because of warmer temperatures.

SOMMER: According to one study, you know, hotter temperatures are responsible for about half of the reduction of the Colorado River since 2000. And you know how I mentioned that California also gets its water from its mountains, you know, the Sierra Nevada...

KWONG: Yeah.

SOMMER: ...The same thing is happening there. Hotter temperatures are melting the snow. And, you know, snow is kind of blindingly white.

KWONG: Yeah. You need those shades when you go skiing.

SOMMER: Yeah, reflects a lot of light. And so when the snow melts earlier, it exposes more soil. Soil is darker than snow. And so it heats up more, and then that melts the rest of the surrounding snow faster.

KWONG: So it's like a self-reinforcing process. Melting snow melts more snow.

SOMMER: Yeah, exactly. Or it just makes the snow evaporate. So you've got water managers at state agencies who are just - they look at the snowpack and they're thinking they're going to get a certain amount of water based on how things worked in the past, and it just doesn't happen. You know, in California, there could be a 15% reduction in the supply from the mountains if there's even just two degrees Celsius of warming.

KWONG: So with these long-term declines, which could happen, drought or no drought, how are states starting to grapple with what to do about this?

SOMMER: It's a very thorny issue because the way that rivers and water sources are divided up is through this system of water rights. And that system is pretty complicated. It's generally that whoever got there first, you know, whether you're a landowner or a city or a state, the older your water right is, the more seniority you have, and you have priority in line. And those rights are considered somewhat, you know, untouchable. Anytime someone proposes big changes, it spawns a lot of lawsuits. The states on the Colorado did negotiate an agreement to use less water if the drought gets worse. And that's why Arizona is going to be taking these cuts later this year. But that's a temporary agreement. You know, they have to negotiate something else that goes beyond 2026 in the future.

KWONG: Yeah. The water rights aspect of this really complicates it. And is the answer to the less water problem more conservation? Like, will everyone in the West have to just accept a future where there's less water to go around?

SOMMER: Yeah, that's the direction it's going. I talked to Alvar Escriva-Bou, a research fellow at the Public Policy Institute of California, about that.

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ALVAR ESCRIVA-BOU: What we are seeing, especially in some parts of California, is that we have been using more water than we have. So the reality here is that we have to make a reduction of water use over the long term.

SOMMER: Most of the water used in the West is used by agriculture. So efficient irrigation is really important going forward. Some cities and farmers are already reducing their water use, and they're finding ways to recycle water.

KWONG: Oh, wow.

SOMMER: But some areas, you know, particularly the ones with those old water rights, there just isn't as much incentive. And at home, if people are wondering what they can do, most people's water use is in their yards, so replacing lawns and switching to drought-tolerant plants is really important. The good news is that, you know, all of those investments, once you make them, they can save water for decades to come.

KWONG: Lauren, this has been a fascinating exploration of the Colorado River stretching back to the 1900s all the way into the future. Thank you so much for bringing us this reporting.

SOMMER: You are welcome.

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KWONG: This episode was produced by Brit Hanson, fact-checked by Indi Khera and edited by Gisele Grayson. I'm Emily Kwong. Thanks for listening to SHORT WAVE, the daily science podcast from NPR.

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