Big changes are coming for the Colorado River soon—and they could get messy

A climate-induced reckoning is playing out on the Colorado River.

The 1,450-mile-long river provides water to over 40 million people and more than five million acres of agriculture across the western United States. But years of punishing drought have reduced its flows to unprecedented levels. In response, the seven states of the Colorado River basin were expected to announce a plan early this week to trim between two to four million acre-feet of their water use in the coming year—about a quarter of the total that flows through the river annually these days.

So far they are failing to do that.

Since 1922, an agreement called the Colorado River Compact has governed how the “Upper Basin” states of Colorado, New Mexico, Utah, and Wyoming, and the “Lower Basin” states of Arizona, California, and Nevada, share the water in the river. The agreements work in times of plenty, but strain under drought. In 2021, the deepening drought forced Arizona and Nevada to make painful consumption cuts, but it has become crystal clear that those efforts were far from enough.

Water levels in crucial river reservoirs have fallen so drastically this year that even those measures, which many hoped would shore up water resources enough to squeak through until the drought broke, fell far short. On June 14, the U.S. Bureau of Reclamation, which operates the main dams and reservoirs on the Colorado, made a stark ask: Within 60 days, the river-dependent states needed to come up with a plan to make the major trims. That deadline has arrived.

On Tuesday, Reclamation officials announced that no deal had yet been achieved. Negotiations, they said, were ongoing.

“The circumstances we face will require swift actions and increased water conservation in every state, from every sector,” said Tanya Trujillo, assistant secretary for water and science at the Department of the Interior, which includes the Bureau of Reclamation. “We simply have no choice.”

Such deep cuts have never been made across the entire river. The magnitude, and the speed with which they need to be achieved, is completely unprecedented, says Felicia Marcus, a western water expert at Stanford University.

“It’s not a surprise, and it’s not yet the apocalypse, but we have to be clear-eyed that we’ve been gambling for at least the last 10 years. And so far, that bet’s not paying off,” she says.

Why does this matter

For more than a century, the Colorado River’s water has propped up communities and growth across the West. Massive hydroelectric dams created Lakes Mead and Powell and generate enough power for 2.5 million homes. San Diego, Las Vegas, Tucson, and many other cities get most of their drinking water from its flow. The river provides irrigation water that turns more than five million acres of arid, sun-soaked land into a place to grow food and other agricultural products for the whole nation.

The river has always had times of abundance and scarcity. The dams and reservoirs along its reaches help to smooth over the sometimes-huge swings, storing water from rain- and snow-rich years to get through the lean ones.

But climate change has upset that system. The Southwest is now in the most severe drought in at least the last 1,200 years made 40 percent worse by climate change than it otherwise would be.

“Scientists have been telling us for years that we can expect flows to diminish by 20 to 30 percent,” says Kathryn Sorenson at the Kyl Center for Water Policy at Arizona State University and a former water manager for Phoenix, and that reality has played out: The river has lost about 20 percent of its flow since 2000. And the trend is expected to continue as the West “aridifies” further.

The problem is that every single water molecule that moves through the river—and in dry years, more—has been spoken for well before it even gets into the river channel. So when flows and reservoir levels drop too low, the delicately balanced water sharing agreements struck a century ago get disrupted, forcing the Colorado compact states to figure out how to make dramatic, and contentious, cuts.

The 1922 pact was based on the assumption that about 17.5 million acre-feet of water, or maybe as much as 20 million, flowed through the river each year—enough today to cover nearly half of Utah in a foot of water. (An acre-foot is enough water to cover a football field, roughly, with water a foot deep.) The agreement obligated the Upper Basin states to provide nearly half that estimated flow—7.5 million acre-feet—to the Lower Basin and allowed the Upper Basin to use up to that same amount, assuming it was still available. Under a 1944 treaty, the U.S. is also obliged to send at least 1.5 million acre-feet to Mexico, where the river historically entered the sea.

But the estimates of the river’s flow proved overoptimistic even before human-caused climate change began to intensify droughts. During the 20th century the flow measured at Lee’s Ferry, Arizona—the boundary between Upper and Lower Basins—averaged just 15.2 million acre-feet. Between 2000 and 2020, that number dwindled to 12.5 million. Scientists warn that to expect more in the future is folly; while wet years will likely come again eventually, the long-term trend in the West is toward more drought, not less.

“This has basically been a hundred years coming, because we’ve always allocated more water on paper than there is in the river,” says Eric Kuhn, former General Manager of the Colorado River District.

Slimming supply, growing demand

Flows on the river may have shrunk, but the demands on it have not. Over the last 20 years, the Upper Basin states have used about 3.7 million acre-feet a year—half of their allotment—and want to use more. The Lower Basin states already use their whole 7.5 million acre-feet. Most years, the river doesn’t even flow all the way to its historical mouth in Mexico, at the Gulf of California.

The consequence? Despite some states having made some hard-negotiated and painful cuts over the past few years, and despite careful reservoir management, the levels at Lakes Mead and Powell have plummeted to never-before-seen lows.

In 2007, the basin states agreed to make a series of cuts when Lake Mead hit certain thresholds. When Lake Mead is full, its surface sits 1,229 feet above sea level (below 895 feet above sea level, the lake is considered at “dead pool”). Under the agreement, the cuts were to start when the lake fell below 1,075 feet above sea level—and they were to start with Arizona, the state with the most recent, or “junior” rights to the river’s water. As the level dropped further, other states and Mexico would have to take less water too.

In 2019, as it became apparent that even more aggressive action might be needed, the states negotiated a “Drought Contingency Plan” that asked for bigger cuts at each risk moment. But even under the very worst-case scenarios, that plan asked all the water users together to trim about 1.375 million acre-feet.

Even that, it is now clear, wouldn't be nearly enough.

In early August of 2021, Lake Mead was at 1,068 feet above sea level, or 35 percent full. That’s when the Bureau of Reclamation, forecasting further declines by January 2022, declared the first-ever water shortage for the river. Arizona is already receiving less water from the Colorado than it used to: Last year, the Central Arizona Project, a major agricultural center, took a 192,000-acre-foot cut.

Yet the water level in Lake Mead has continued to fall. As of this month it had dropped to 1,041 feet and 27 percent full.

In mid-June, with dead bodies and shipwrecks emerging from Mead and other shrinking reservoirs, U.S. Bureau of Reclamation Commissioner Camille Touton announced that the river states needed to figure out a way to cut two to four million acre-feet of use as soon as possible—a much bigger request than even the 2019 plan had envisioned.

“We tried to put Band-Aids on the way we managed the river and they just weren’t getting us what we needed,” says Jennifer Gimbel, the interim director of the Colorado River Center at Colorado State University. “We thought we had more time. And that much water in that short a time is very difficult to get ahold of.”

The drastic cuts are necessary to keep the reservoirs full enough so the hydropower plants at their mouths continue to operate, the Bureau of Reclamation says. If that water level drops below the intakes, it puts the whole infrastructure at risk. At the Hoover Dam on Lake Mead, the power production can’t happen if the level drops below 950 feet above sea level.

How will they do it?

The Bureau of Reclamation’s Touton gave the states 60 days to come up with a plan for the cuts. The details of how to achieve them were left up to the states. The only certainty is that they will be painful, controversial, and dramatic—and they’ll have to happen fast.

Now, absent a deal, the pressure to negotiate quickly is even higher.

Arizona, with junior water rights, has been planning for years how to manage this situation and is expecting to have to make more cuts, Sorenson says.

The most unprecedented changes could come in California, which has historically used an average 4.4 million acre-feet a year. It has some of the most “senior” rights, meaning it’s the last to feel the pinch during shortages. But even the vast irrigated zone in the Imperial Valley—the source of about two-thirds of the U.S.’s winter produce, and an area that has almost never had water curtailed—could see fields fallowed this year.

The biggest, and quickest, trims are likely to come from agriculture, says Marcus, a western water expert at Stanford University. By fallowing fields, water that would otherwise be diverted into crops can stay in the reservoirs. The new Inflation Reduction Act allocates $4 billion to drought aid along the river, some of which could be directed toward farmers fallowing their fields or transitioning to lower-water technologies.

Cities in the seven states will also likely have to adjust—even though they account for a small fraction of total water demand, and even though many have already taken serious steps to conserve water. Phoenix, Sorenson points out, has added six million people over the past 50 years but its water demands have stayed more or less the same. Nonetheless, she says, “everyone needs to step up and do their fair share.” Los Angeles, which gets a chunk of its water from the Colorado, has already imposed outdoor watering restrictions this summer.

Also crucial to the ongoing negotiations are the 30 Native American tribes in the basin, which hold water rights to about a quarter, and potentially more, of the river’s current flow. Those rights have not historically been fully recognized or apportioned, but tribal leaders are looking to bolster their position during negotiations. They want access to the water to which they are entitled and to participate in solutions for making it through the ongoing drought.

Many experts hope the states use this moment to rethink their use of the Colorado River more deeply—and that the cuts, however painful, become more permanent and bring demand in line with the real supply.

“We have been kicking the can down the road for a long time now, and now we’re just kicking it into the wall,” says Kevin Wheeler, a hydrologist and river expert now at the University of Oxford. In a recent analysis, he and his colleagues proposed re-jiggering the basins’ allocations to account for climate change; they suggested cuts roughly the same magnitude as those Reclamation asked for.

“Ultimately, these are going to have to become permanent,” says Kuhn.

No matter what happens, life for everyone within the river’s vast sphere of influence will soon feel these changes. “It’s definitely history in the making,” says Gimbel.

This story, originally published on August 15, 2022, has been updated.