How a 100-year-old miscalculation drained the Colorado River

By now, you may have heard that the Colorado River is drying up.

The river’s flow is down by about 20 percent, compared to the 1900s, and the two largest reservoirs it feeds are less than a third full. The water in Lake Mead, the nation’s biggest reservoir, has dropped more than 150 feet in the last two decades, leaving little water for the more than 40 million people who depend on the river.

Part of the reason why the Colorado River is shrinking is the dwindling amount of snow and rain. The West is in its 23rd year of drought, which research suggests could be the driest period in the last 1,200 years, made worse by climate change.

Then there is the sheer number of cities and farms that are sucking down water. About three-quarters of all water that humans consume from the Colorado River goes toward irrigating farms, which, among other things, supply nearly all of the nation’s winter veggies.

But a key reason why the Colorado River is running out of water has more to do with math than anything — bad math.

One hundred years ago, government officials divvied up water in the Colorado River among the seven states that rely on it including Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming. The agreement, known as the Colorado River Compact, was based on one critically important number: the total amount of water that the Colorado River can supply yearly.

John Locher/AP

Ignoring the best science of the time, officials claimed the river could provide about 20 million acre-feet per year (an acre-foot is the amount of water needed to fill an acre with one foot of water), according to the 2021 book Science Be Dammed: How Ignoring Inconvenient Science Drained the Colorado River. That number was way too high, the authors write, meaning that officials promised states water that simply didn’t exist.

“They had conjured up a larger Colorado River than nature could actually provide,” wrote authors Eric Kuhn, a retired water official, and John Fleck, a writer and former director of the University of New Mexico’s Water Resources Program. “The twenty-first century’s problems on the river are the inevitable result of critical decisions made by water managers and politicians who ignored the science available at the time.”

I spoke to co-author John Fleck about how officials in the past miscalculated so badly, and where we go now. Our conversation has been edited for length and clarity.

How much water is left in the Colorado River?

Benji Jones

For anyone not following what’s happening with the Colorado River, catch us up: How much water has the river lost and how close is it to drying out?

John Fleck

Twenty years ago, the big reservoirs that hold most of the river’s water were close to full. But two decades of drought, amplified by climate change — combined with the fact that we’re continuing to use a whole lot of water — have largely emptied the reservoirs.

We’ve reached the point where the reservoirs are no less than a third full in terms of the available water supply that we might use. We’re at the danger point.

Tayfun Coskun/Anadolu Agency via Getty Images

Benji Jones

You’re talking about the reservoirs Lake Powell and Lake Mead?

John Fleck

There’s also a cluster of other reservoirs that help support the operation. But yes, it’s mainly Lake Powell and Lake Mead, the two biggest reservoirs in the nation. They have the ability to store five times the river’s annual flow, which we burned through in the last 20 years.

Benji Jones

Are there parts of the river that are totally dry, where you could see, say, cracked earth?

John Fleck

Yes, and this was a stunning revelation for me. The very bottom of the river, where it leaves the United States and enters Mexico, used to be this vast delta — wild and wet and full of beavers and marshes and estuaries. But the river now stops at a place called Morelos Dam, on the US-Mexico border.

Karl Flessa

Downstream from the dam there’s a little trickle of water that’s maybe 10 to 15 feet wide, and then it peters out into the sand. Then you just have dry riverbed. That’s because we’ve taken all the water out of the river upstream to use in our cities and farms.

Benji Jones

The Bureau of Reclamation, the federal agency that manages water in the US, has announced cuts related to the level of water in the reservoirs, known as Tier 1 and 2 shortages. How does that work?

John Fleck

Over the last 15 years, river managers have faced a looming problem: We’ve been taking more water out of the river than it can provide. So they negotiated a series of agreements that say if, for example, Lake Mead drops to a certain level, there’ll be cutbacks. If it drops even more, the cutbacks will get bigger.

Those cutbacks are now kicking in. But what we’ve since realized is that the cutbacks weren’t made soon enough and they weren’t deep enough, so the bottom is dropping out.

Bad math and ignoring science helped dry the river out

Benji Jones

How did we get here? There’s climate change and drought. But you write about some historical oversights. What happened?

John Fleck

In the early 20th century, the US Geological Survey sent out this guy named Eugene Clyde LaRue to try and measure the Colorado River. LaRue started to see that, beyond the time horizon that we’d been measuring the river so far [a couple of recent decades], there were some really big droughts. He concluded in a 1916 report that the river is subject to big droughts on timescales of 10-to-20 to 50-to-100 years. It doesn’t just stay wet.

The negotiators of the Colorado River Compact — the foundational document for figuring out how to divide up the river and decide who gets what — needed this information. They needed science. But they came together to figure this out without LaRue. They sidelined him. They ignored his science that said there’s been big droughts.

Instead, the negotiators looked at a much more recent period [of time] that had been extraordinarily and unusually wet. They said the river’s got plenty of water to build all these farms and to build all these cities. They just ignored the science because it was inconvenient.

Benji Jones

Why was it so inconvenient to be realistic about the amount of water in the river?

John Fleck

The promise of a lot of water made the political deal-making easier. You could divide up the river and say to each of the seven states: “You want to irrigate a whole bunch of acres? Plenty for you. You want to pump a bunch of water across the desert of California? Plenty for you.” You didn’t have to have hard conversations about what life under limitation was going to be like.

Benji Jones

How big was the difference between what LaRue measured and what the negotiators ultimately used to divvy up the river’s water in the 1922 Colorado River Compact?

John Fleck

Negotiators believed — and negotiated a deal that said — there was as much as 20 million acre-feet flowing from the river each year. LaRue’s estimate was closer to 15 million. Today, we know it’s 12 million. But that’s the climate change world. It was a big gap.

Benji Jones

Is that gap ultimately why we’re in this position today? Basically, 100 years ago, regulators over-allocated water of the Colorado River, based on faulty numbers?

John Fleck

Yes. You have communities across the West who made good-faith decisions to build cities, farms, canals, and dams based on what they thought was a promise of water. They were told that there was enough water. That turns out to have been bogus.

Then, during the drought of the 1930s, and during the drought of the 1950s, it became clear that LaRue had been right [about how much less water there is]. People who are still trying to insist on their “paper” water allocations [based on the compact] are making the same mistake that the compact negotiators made 100 years ago.

Cities have learned to use less water — but there’s still not enough

Benji Jones

Are regulators now taking into account what science says about the river?

John Fleck

I would like to just say yes. There’s a whole bunch of people in the system who understand the importance of using the best available science. My favorite example of this is Las Vegas, Nevada, and the Southern Nevada Water Authority, which really has been taking climate change seriously.

The difficulty is at the political interface. It is difficult for a hypothetical governor to go before their voters and provide them with bad news about water. What a governor really needs to say is: “We have a lot less water, we have to change.”

[The 100-year-old Colorado River Compact, wrong numbers and all, is still the primary agreement upon which management of the Colorado River is based.]

Brian van der Brug/Los Angeles Times via Getty Images

Benji Jones

How about communities and cities along the river? Are users getting realistic about how much water they can consume?

John Fleck

Different communities approach risk differently.

Big cities tend to be the most realistic. It’s hard to find a major city in the West that has not gone to enormous lengths to invest in the necessary conservation programs. Almost every major metropolitan area that depends on the river’s water is seeing their total water use go down, even as their populations rise.

Agricultural communities face a harder time because, really, the only thing you can do to use less water is to farm less. So you’re asking them to give up both a portion of their economic livelihood and also their cultural identity as farmers.

Even though most communities can adapt to use less, they’re afraid they can’t. That fear leads to this winner-take-all, fight-over-water approach rather than collaboration. That’s why we have not been able to reduce our use fast enough to halt the decline of reservoirs.

Benji Jones

Is demand for water increasing? I’ve always thought that was a problem, too.

John Fleck

It’s actually not. Water use is going down. The upper part of the Colorado River Basin is, on paper, entitled to 7.5 million acre-feet a year. That was always an unrealistically large number. After building out all our projects by the late 1980s, the water use there has been relatively stable at around 4 million [acre-feet per year], though it fluctuates wildly year to year.

If you look at the lower Colorado River Basin, water use peaked in 2002, and has been steadily declining. There’s been substantial reductions in a couple of the major agricultural areas. The Imperial Irrigation District of California is the largest farm district and their use has dropped dramatically. Urban use has also been going down. We’ve seen water use decoupled from population growth.

Who loses when the water runs out

Benji Jones

Earlier this summer, the Bureau of Reclamation asked the seven states that depend on the river to cut an additional 2-4 million acre-feet per year. How much water is that and how disruptive will it be?

John Fleck

That’s between one-sixth and one-third of the average annual flow of the Colorado River right now. It’s a lot of water.

What we mean when we say “the flow of the river” depends on which period of time you’re looking at, because it’s constantly varying. When I say, “one-sixth to one-third,” that’s of the river’s flow in the 21st century, when we’ve been experiencing drought and climate change.

There’s going to be a really big disruption, and it’s going to happen one of two ways. Districts and states could figure out now how to come up with those 2-4 million acre-feet, voluntarily, working from the bottom up. Or the disruption is going to come within a year — or two or three — when the reservoirs are just freaking empty. Those are the two options.

The lovely third option is we have a few years of monstrous snowpack [melting snow in the spring feeds the river]. I’m not beyond hoping for that third option.

Benji Jones

Who will suffer the most as cuts continue?

John Fleck

The most important set of users is tribal communities who were promised water by the nation when we were busy stealing their land. We haven’t given it to them yet. Even the language I use is problematic. It’s not about giving them water that’s ours but acknowledging that this water was theirs to begin with.

There are tribes who don’t have their water allocations — or who have water allocations but not the federal largess to use it in the same way as all the Anglo communities, like my own. It’s a significant issue across large parts of the basin.

Then there’s the environment. Long ago, we decided that we didn’t care about the environment, but now, as a society, our values are shifting. So figuring out how to claw back some of that water for the environment is one of the really big challenges.

Benji Jones

What is your most brilliant solution for solving this water shortage?

John Fleck

I always punt on this question. It doesn’t matter what I think and it doesn’t matter what I say. For a solution to be effective, it has to emerge from the people who are using water themselves. What I can do is make clear the scope and the scale of the problem. You can’t impose solutions on people. It just doesn’t work.

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