Part of the issue The 100-year-old-mistake that’s reshaping the American West from The Highlight, Vox’s home for ambitious stories that explain our world.

The Colorado River provides water for irrigation, power generation, recreation, and habitats for endangered species. But the 40 million people who drink from this critical artery have watched it wither amid the region’s worst dry spell in more than 1,200 years.

This massive drought, sometimes called a megadrought, settled over the Western United States two decades ago, and precious precipitation has flowed and faded from year to year. But since 2020, the region has faced essentially a drought within a drought. In an already water-sparse region, this has led to some of the driest conditions the Western US has seen in memory.

“It’s kind of like the slowest-moving freight train that you know is going to hit you,” said Cynthia Campbell, water resources management adviser for the City of Phoenix. “At the same time, what we’ve seen in the last couple of years has been an enormous acceleration that frankly we didn’t expect.”

This year, the two largest reservoirs in the US, Lake Mead and Lake Powell, saw water levels dip to record lows. The falling waterline revealed relics and corpses previously lost for decades, leaving behind stark bathtub rings along the surrounding canyons. In turn, the Hoover Dam and the Glen Canyon Dam that impound these reservoirs saw their hydroelectric power production dwindle.

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As electricity production dropped off, demand picked up as another heat wave scorched the West. To survive in the extreme heat that’s increasingly a fact of life, millions of people switched on fans and air conditioners, pushing the power grid to the brink of blackouts.

Climate change is already pushing parts of the world past the limit of human survivability for parts of the year. The worry now is that all these factors shaping the future of the Colorado River — drought, population growth, energy demand — could amplify and converge again as average temperatures continue to rise, disrupting life for the denizens of the West, one of the fastest growing regions of the US.

The vanishing water, the rising temperatures, and the growing thirst threaten to undo what made the West such an appealing place to live in the first place. With triple-digit summer weather and little water to cool off, life in the Colorado River basin could become untenable for millions without drastic cuts to consumption if a more severe drought parched the landscape. Meanwhile, the powerful river that carved one of the deepest canyons on Earth would turn into a fragmented skeleton of its former self, and the farms, businesses, and industries that relied on its bounty would sputter to a halt.

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“Water supplies for agriculture, fisheries, ecosystems, industry, cities, and energy are no longer stable given anthropogenic climate change,” Camille Calimlim Touton, commissioner of the Bureau of Reclamation, told Congress in June 2022.

The Colorado River is one of the most heavily engineered waterways in the world, and past decisions and ongoing withdrawals are exacerbating the drying. From a miscalculation of the water available to begin with, to failing to account for evaporation, to prioritizing irrigation for cattle feed above people, policies are arguably the biggest driver of water shortages in the West. The rules around water sharing have created a political crisis as states debate how to allocate the dribs and drabs of what’s left.

This year, an unusually wet winter has provided much-needed respite for the Colorado River Basin. Two-thirds of the river’s annual flow starts as snow in the Rocky Mountains, and snow levels are well-above what’s typical for this time of year. That has relieved some pressure and bought time, but it’s nowhere near enough to fill the deficit.

Earlier this month, the federal government outlined its plans to impose water cuts if states along the river don’t agree to their own reductions. The proposal considers three scenarios. One of them would force equal cutbacks among the states, overturning the longstanding “first in time, first in right” water allocation system.

Looking at the past and the future, scientists warn that the drought could still carry on, especially as the climate changes. The key question now is how much worse can the situation get? The answer depends on natural weather variability, how much more humanity changes the climate, and how people respond to the crisis now. So it behooves all the thirsty souls along the drying river to prepare for a world with less to drink and reckon with what it means to survive in the West.

How bad can it actually get?

Mapping out the future of the Colorado River is critical for making decisions today. It’s tricky to game out, but experts warn that more dire outcomes are possible.

“It’s very difficult to say because there are so many variables, and we are really just learning about many of them,” said Sarah Porter, director of the Kyl Center for Water Policy at Arizona State University. “We’re just learning about how the system responds to hotter, drier conditions.”

History, however, offers some insight. In a study published last year in the Journal of the American Water Resources Association, researchers analyzed tree rings and historical records to reconstruct past water flow levels along the Colorado River, including historic droughts. They then plugged three of those drought scenarios into climate models to see how they would change as average temperatures rise.

Based on current trends and commitments to curb greenhouse gas emissions, the Intergovernmental Panel on Climate Change estimates that the planet will warm by 4.9°F (2.7°C) by 2100. Warming has complicated effects on drought though; some parts of the world will get wetter and others drier. Several studies, however, show that warming will further dry out the Colorado River Basin, and while droughts do occur in natural cycles, climate change is increasing the likelihood of megadroughts in the region. Factoring this in, the researchers reported in their paper that “even more severe droughts are possible.”

The team constructed their study around Lees Ferry, a point downstream from the Glen Canyon Dam in Arizona. Between 1906 and 2018, the average flow rate of the river at Lees Ferry was 14.76 million acre-feet per year. One acre-foot is the amount of water needed to flood an acre of land one foot deep, or about 326,000 gallons. Looking at the current megadrought, between 2000 and 2021, the average flow rate fell to 12.3 million acre-feet per year.

These deficits are why the gargantuan reservoirs on the Colorado River have fallen to record lows. Looking ahead, the researchers said that a plausible drought scenario to plan for is a shortfall of roughly 20 to 30 million acre-feet of water over five years. These are some of the most extreme scenarios in the historical record, but as average temperatures continue to rise, they won’t be such outliers.

“The climate comparison part of the paper sought to show that while extreme based on historic data, they were not too extreme based on climate projections,” author David Tarboton, director of the Utah Water Research Laboratory, said in an email.

Those historical droughts, however, occurred in a much more free-flowing Colorado River with a lot fewer people depending on it. Should they recur, the more extreme droughts will be much more impactful.

Dams on the Colorado River will bear the brunt of these impacts. If water levels fall too low, hydroelectric generators like the Hoover Dam and Glen Canyon dam, which peak at 3.3 gigawatts of power output between them, could fall silent. There’s an even more ominous outcome known as dead pool. This occurs when water levels in a reservoir fall below the intakes of the dams that created them. The river effectively comes to a halt.

US Bureau of Reclamation/US Department of the Interior

That doesn’t just threaten electricity production; it puts the environment at risk. Threatened and endangered fish like the humpback chub and Colorado pikeminnow will likely see their numbers drop further. The mighty river that carved the mile-deep Grand Canyon would see only a trickle of its former self. Tourism on the Colorado River is a $9 billion-a-year industry, but that will drop off a cliff with fewer options for rafting, fishing, and boating.

Many of the canals and branches from the Colorado River that channel drinking water would also run dry. Arizona gets more than one-third of its water from the river. The 4.9 million residents of the Phoenix metro area receive some of this water through canals that are part of the Central Arizona Project, but they are fortunate enough to have the Salt and Verde River systems and groundwater to cushion their supplies as well.

“We could meet our demands even with zero [water] in the canal, but it would be very difficult, it will be very tight,” said Phoenix’s Campbell. “We would have to immediately ask our customers to curtail.” Residents would have to curb their watering of lawns and golf courses, and limit filling swimming pools.

But the kind of drought that would create a dead pool would stress these other water sources as well, and some are already being overused. Earlier this year, Arizona Gov. Katie Hobbs released a previously unpublished report that part of Phoenix is overdrawing groundwater and failing to maintain levels required by law, halting thousands of planned new property developments in the area.

Throughout the region, agriculture is the largest water user. Crops and livestock in the Colorado River basin generate $60 billion per year. The largest share of water goes toward growing cattle feed crops like alfalfa. Under a more severe drought, farmers will have to make tough decisions about whether they can grow anything at all. Winds over fallow fields and dry streams could then whip up dust that hampers air quality and increase respiratory illnesses. One study found that increasing aridity due to climate change in the southwestern US would increase premature deaths due to dust by at least 24 percent among adults over 30.

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As for residents, glimpses of the future are already emerging. The Rio Verde Foothills, a suburb of Scottsdale, Arizona, saw its water supplies cut off in January as Scottsdale decided it could no longer sell water to the community due to the drought. Homeowners had to scrounge for their own water supplies. According to the New York Times, some of the 1,000 residents in the community of half-million-dollar houses had to forgo bathing and washing dishes.

The biggest uncertainty in any drought scenario, however, is how people will respond. The seven southwestern states that drink from the river — Arizona, California, Colorado, Nevada, New Mexico, Utah, and Wyoming — negotiated their allocations based on an assumption of more water than the basin can consistently provide, governed by a complicated seniority system that ends up giving more water to farmers downstream than residents further up the river. They are already struggling to come up with a plan to reduce their water use under the existing drought, and if the dams reach dead pool status, they will have to sip even less.

That, in turn, is fueling tension between states, and the federal government may have to step in if states won’t cut their water intake on their own. The Interior Department’s proposal examined a do-nothing scenario, a scenario with cuts based on existing water rights, and a scenario that would distribute the cuts evenly. That last plan could reduce water deliveries to Arizona, Nevada, and California by up to 25 percent.

Now the threat of an even drier river is helping push states to the negotiating table.

“Everybody sees the dead pool as a possibility and is working to avoid dead pool,” said Porter, “because a dead pool would be really catastrophic.”

At stake is the very vision and ideal of the West, one predicated on constant growth and engineering a way out of every problem. Hitting a hard limit of a vital resource means residents will have to rethink and forgo some of the things they’ve grown accustomed to, like golf courses, lush green lawns, and large, power-hungry homes. But the effects of the drought will reach all Americans on their plates, particularly the country’s ravenous appetite for beef and dairy.

An unchecked and unmitigated prolonged drought under a warmer climate threatens to collapse the economy of the region. Drought has driven migrations throughout the world and through history, and could do so again in the West. For people counting on the Colorado River to slake their thirst, that could force them to pull up stakes.

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There’s precedent: The drought-fueled Dust Bowl of the 1930s ignited a wave of migration from the Southern US toward the West. Now the threat of climate-worsened disasters – not just drought, but wildfire and sea level rise – is driving more people to head to somewhat safer ground. Drought is already one of the biggest drivers of migration around the world, and future warming could force far more people to move.

Nonetheless, it may still be possible to survive a more extensive drought along the Colorado River, but it will demand sacrifices, investment, new technologies, and giving up old assumptions.

What can we do about it?

Though the situation is dire and could get worse, there are solutions that would allow people to endure, even thrive, in a warmer, drier Southwest. “Being that it is a largely human-caused problem, there are human-caused solutions as well,” said Alicyn Gitlin, Grand Canyon program manager at the Sierra Club.

One of the most impactful strategies is reducing water use for agriculture. That could involve growing less water-intensive crops and paying farmers not to grow during periods of extreme water stress. Cutting consumption of beef and dairy would help reduce demand for some of the thirstiest crops.

Outside of agriculture, though, people living in the Southwest are already learning to do more with less water. Population growth and water consumption have substantially decoupled. One study looking at 28 water utilities serving 23 million people over two decades found that water deliveries fell by 18 percent while the population grew by 24 percent. The techniques that drove this trend include variable water pricing; recycling rainwater; plumbing retrofits and more water-efficient appliances; as well as drought-tolerant landscaping. Doubling down and using other tactics like harnessing gray water from appliances, showers, and sinks could continue to drive down water use further.

“There is still way too much water being used for outdoor landscaping, which can account for half or more of some cities’ water use,” said the study’s author Brian Richter, president of Sustainable Waters, a drought-focused think tank, in an email. “And whatever is used outdoors should come from capturing rainwater from roofs, or from larger stormwater capture ponds, not from public water supplies!”

Electricity production is also a major water guzzler, and not just hydroelectric dams. Most power plants rely on steam to turn their generators and water for cooling. These plants have also become more water-efficient. In 2015, electricity required 14,928 gallons of water per megawatt-hour. In 2020, it was 11,857 per MWh. Some utilities are studying dry cooling technology, which can use up to 95 percent less water.

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The growth of wind and solar power, which require little water to operate, has also chipped away at water demand from the energy sector and could cut it further.

One of the most drastic proposals is to get rid of the Glen Canyon Dam entirely. That would free up the water impounded in its reservoir, restoring more natural flow to the river. That in turn would replenish ecosystems and provide more water downstream. It would also restore access to lands that are important to Native American tribes in the region, including Navajo, Hopi, Zuni, Paiute, and Pueblo.

Over the long term, cutting greenhouse gas emissions would limit future warming and thus reduce the chances of major droughts across the Colorado River basin. The immediate task, though, is for states along the river to come up with a set of cuts they can all agree to.

The Interior Department is also putting together revised guidelines for operating the Hoover Dam and the Glen Canyon Dam. “This process will help to provide the Department the alternatives and tools needed to address the likelihood of continued low-runoff conditions, and therefore reduced water availability, across the Basin over the next two years,” a spokesperson for the Interior Department said in an email. The agency expects to finalize these new guidelines in August.

The snow and rain this past winter have bought some breathing room for the discussion, but the worry is that this will be another excuse to ship the unavoidable difficult decisions further downstream.

“I think we were just at the point where we were getting people to really pay closer attention to this, and we could turn around and lose all of that momentum,” Campbell said.