For farmers in the deserts of central Arizona, success and failure is defined by who has water and who does not. At the moment, Dan Thelander is still among the haves.
Inside a municipal building in Pinal County, Thelander rolls a map out across the board room table.
On the patchwork of brown desert and green farmland in front of us, Thelander points out the parcels of land where he and his brother, son and nephew grow cotton, alfalfa and several other crops.
About half the water he uses to irrigate his land is pumped out of ancient aquifers deep beneath the desert floor. The other half, however, originates hundreds of miles away at the headwaters of the Colorado River.
The Colorado River
The water begins its journey high in the Rocky Mountains of Colorado, Utah and Wyoming, where it first falls as snow.
As winter fades and the snowpack melts, water drains into the mountain streams and tributaries that feed the Colorado River.
The river’s vast drainage area is divided into two regions: the Upper and Lower Basin. Around 90% of the river’s flow originates in the Upper Basin.
After flowing down from the Upper Basin, the river snakes its way across the Southwest, eventually reaching Lake Mead near Las Vegas. From there, a system of dams, canals and pipelines channel it into the irrigation ditches that water Thelander’s thirsty fields in Pinal County.
Today, this river system supplies 40 million people in seven western states and Mexico, and irrigates more than 5 million acres of farmland on its way into Mexico and the Gulf of California.
Las Vegas relies on the river for 90% of its water supply, Tucson for 82% and San Diego for around 66%. Large portions of the water used in Los Angeles, Phoenix and Denver also come from the river, and experts say these booming metropolises would not have been possible without its supply.
The Colorado River crisis
But a crisis is unfolding, and farmers, scientists, water managers and policy makers across the Southwest are increasingly alarmed.
Water managers have long recognized that the river is plagued by overuse. But over the last two decades, demand for the river’s water has often outstripped its supply. Since 2000, the river’s flows have shrunk by roughly 20% compared to the 20th century average. At the same time, its two main reservoirs — the savings account for the entire system in times of drought — have drained rapidly.
The Colorado River main reservoirs
Lake Mead — the largest manmade reservoir in the US, which is fed by the Colorado River — recently sunk to its lowest levels since the lake was filled in the 1930s. Its water levels have fallen more than 146 feet since their peak in January of 2000, and the lake is now just 35% full.
Lake Powell, the river’s second largest reservoir, sits at 32% of its capacity. As water levels drop, billions of kilowatt hours of hydroelectricity that power homes from Nebraska to Arizona are also at risk.
“We’re in uncharted territory for this system,” says Jeff Lukas, an independent consultant and former research scientist at the University of Colorado at Boulder, where he focused on water issues for 20 years.
First official water shortage
On Monday, the US Bureau of Reclamation declared the first-ever official shortage, which will trigger the largest mandatory water cuts to date in the Colorado River Basin. And after decades of receiving water from the Colorado River, the spigot could soon be turned off on many farms here, including Thelander’s.
While the farmers knew this day would come, a harsh reality is setting in: To stay in business, they’ll need to pull more water from below ground.
Back on the table, Thelander points to the diamonds and circles that dot the map. Those mark the locations of new groundwater wells that his irrigation district is considering — the first new ones they have drilled in decades, Thelander says.
For much of the last century, Colorado River management has focused on choosing who will be allowed to stick their straw into the river next and how much water they can take. At times, that process has sparked major disputes — with some leading all the way to the US Supreme Court.
Now, many of the basin states are having a more painful discussion: deciding who will receive less water — and how much. Experts say the next phase in the river’s history could be even more contentious.
The current Colorado River guidelines expire in 2026, and early negotiations are already getting underway for a new framework to determine how to divvy up its water. But by the time officials from the states, Mexico, Native American tribes and the federal government convene, it is likely that the river’s water supply will be even more tenuous than it is today.
History of the Colorado River crisis
Scientists and water policy experts say that the science is clear: The Colorado River’s supply will likely shrink further as the planet warms. Given what we know, many say we will have to use even less water in the future.
But will the states be able to agree to new guidelines that reflect this reality? And with the Southwest’s growing urban centers and farms both reliant on the river’s supply, who will be willing to take less water?
How elected officials and water managers answer those questions will decide the fate of the most important water resource in the American West — and the millions of people who rely on it.
The roots of this current water crisis can be traced back nearly 100 years to the signing of the Colorado River Compact.
In November of 1922, with then-Secretary of Commerce Herbert Hoover overseeing the deliberations, delegates from all seven Colorado River Basin states convened in Santa Fe, New Mexico, to hammer out the guidelines.
From the start, the compact negotiations were contentious. Squabbles erupted over details big and small, from how to measure the river’s flow to how to portion out its supply.
Efforts to reach a deal began in January of 1922 and resumed in November, when delegates from the states gathered in Santa Fe, New Mexico. After two weeks of deliberations, they finally reached an agreement on November 24, 1922.
Then-Secretary of Commerce Herbert Hoover presiding over the 1922 signing of the Colorado River Compact. US Bureau of Reclamation
From the Southwest’s cities to its farms that feed the world, water managers say much of what we see today would not exist without the dams, canals and pipelines that the compact paved the way for.
“[The Colorado River] is the lifeblood of the American Southwest,” says Jeff Kightlinger, who led Southern California’s Metropolitan Water District for 15 years before his recent retirement. “None of these cities would be possible but for the Colorado River and the development of it for all of these regions.”
Over the course of the 20th century, new agreements and court decisions further divided up the river’s supply among the seven basin states, Mexico and the region’s Native American tribes. But there was a serious flaw in the original compact — one that, in part, explains why the river is facing its first-ever shortage today.
When the delegates met, they agreed to give the Upper Basin (made up of Colorado, Wyoming, Utah and New Mexico) and the Lower Basin (California, Arizona, and Nevada) each 7.5 million acre-feet of water to use on an annual basis.
How the Colorado River’s water is divided up
The Upper and Lower Colorado River Basins are each allocated 7.5 million acre-feet of water per year. Mexico also receives 1.5 million acre-feet of water annually.
Upper Basin states are entitled to a percentage of the Upper Basin’s overall water allocation. Meanwhile, Lower Basin states and Mexico are apportioned a set amount of water each year.
Arizona is also allocated an additional 50,000 acre-feet/year from the Upper Basin, because a small part of the state lies in the Upper Basin.
Those portions were based on estimates that the river’s flow totaled roughly 16.4 million acre-feet each year. That was more than enough to meet the demands of the states. However, data shows those estimates exceed the amount of water the river actually provides in most years.
Analysis of US Bureau of Reclamation (USBR) data shows that between 1906 and 2019, annual flows on the river actually averaged just under 14.8 million acre-feet. Over the last two decades, flows have been even lower — just an estimated 12.3 million acre-feet on average each year.
The Colorado River Compact was signed after several wet years, leading states and the federal government to overestimate the river’s flows. But data shows that over most of the last 100 years, the river’s flows have been well below their pre-compact levels.
Up until the 1990s, the Lower Basin states were not using all the water they were entitled to on paper. This allowed officials to let the river’s water accounting problem persist for decades, experts say.
Water use in the basin has increased steadily over the course of the 20th century. Higher demand has outpaced the level of new water supply coming into the system, and this imbalance explains, in part, the depletion of the system’s main reservoirs.
“Through the 20th century, it was easy for political actors to ignore that reality …,” says John Fleck, a professor at the University of New Mexico who has written several books on the Colorado River and water issues in the West. “There was slack in the system because it took us a century to build all the dams and diversions that people dreamed about in the 1920s.”
A river stretched beyond its limits
As water rights were granted and new canals were built, that slack has gradually disappeared.
Data shows that the over-allocation problem became more apparent in the years after one of the last big straws was inserted into the river.
The Central Arizona Project (CAP) — a massive, 336-mile canal and pipeline system that carries Colorado River water across the desert to Phoenix, Tucson and farms and towns in between — was authorized by Congress in 1968.
Before the CAP was completed in the 1990s, heavy groundwater pumping in central Arizona was sucking aquifers dry at an alarming rate. The CAP promised a renewable, reliable source of water.
With no infrastructure to deliver Colorado River water to cities in the middle of the state, Arizona was also only using about half of its Colorado River allocation before the CAP was completed, according to Ted Cooke, the general manager of the CAP.
The Central Arizona Project (CAP) began diverting water in the 1980s and is one of the reasons why water use in the Lower Basin rose through the early 2000s.
California had long opposed the project, so to gain support from the state’s congressional delegation, Arizona made a key concession: That in the event of a shortage, fulfilling California’s water deliveries would take priority over meeting the needs of CAP water users.
Now, with water cuts looming next year, the CAP’s status in the Colorado River’s pecking order is proving significant.
As water levels in Lake Mead fall, Lower Basin states and Mexico will face cuts to their supply. Arizona will see the largest reductions.
Water cuts in the Lower Basin and Mexico are tied to the water levels in Lake Mead
As Lake Mead’s levels have fallen, Arizona, Nevada and Mexico are already receiving less than their full allocations of water.
And with the lake projected to be even lower next year, deeper cuts will take effect in 2022. Arizona faces the most severe reductions.
In Arizona, the water cuts will have the greatest impact on lower-priority water users served by the CAP, like farmers in Pinal County.
But if water levels in Lake Mead continue to sink in the years to come, California could also face cuts to its water supply.
Some cities and tribes in central Arizona could also face reductions if the lake drops to critical levels.
If the lake drops below 1,025 feet above sea level, Arizona would receive less than 75% of its full Colorado River water supply.
Arizona farmers like Dan Thelander have known for years that their supply of Colorado River water would eventually be phased out. They just didn’t expect it to happen so soon.
A drought that began more than two decades ago, along with the effects of higher temperatures due to global warming, have rapidly sapped the river’s flow. And in the long-term, scientists and water policy experts say those problems pose a threat to users far beyond the farms of Pinal County.
Droughts are temporary. The drying up of the river may not be
The Colorado River’s drainage basin spans some 246,000 square miles but most of its flow originates in a handful of snow-capped mountain ranges in southern Wyoming, western Colorado and northeastern Utah, according to Jeff Lukas, the research scientist and water consultant.
The river flows through some of the country’s most arid land, so the snow that accumulates in those areas is critical. In most years, snowmelt is responsible for about 80% of the river’s water supply, Lukas says.
Many scientific studies have examined why there is less water flowing into the river. Nearly all have found the fingerprints of human-caused climate change.
The first, and perhaps most cited, explanation is the ongoing “megadrought,” which began in the year 2000.
A study published in the journal Science in 2020 found that the period from 2000 to 2018 was the driest stretch the Southwest has experienced since the 1500s, and that nearly half of the drought’s severity could be attributed to global warming.
“When you have more evaporation, you have less water left over to come down the river.”
As dry as it has been, the study found that this may only be the beginning. Past megadroughts have lasted longer than the current one.
But a lack of snow and rain doesn’t fully explain what is happening to the Colorado River. And droughts, after all, are temporary. Some scientists say the evidence shows the river’s shrinking supply is likely not so fleeting.
Brad Udall, a climate scientist at Colorado State University, argues the river’s plight is best summed up by another term: aridification.
Broadly speaking, aridification is a shift to a new climate state dominated by water scarcity and driven by the effects of hotter temperatures. Temperatures across the basin have risen by an average of 1.4 degrees Celsius (2.5 degrees Fahrenheit) over the last century.
“[Warmer temperatures] are just this constant, year in and year out, force on the system,” Udall says.
As temperatures warm, the amount of precipitation that falls as snow decreases, and the snow that does fall melts earlier, according to Chris Milly, a hydrologist with the US Geological Survey who co-authored a study last year examining the river’s decline.
Snowpack reflects much of the sun’s energy back into space. But as the snow melts earlier and leaves behind exposed soil, more heat from the sun is absorbed by the ground. This leads to more evaporation, which means less runoff ends up in the river, Milly said.
“Evaporation is how the river basin cools itself,” Milly says. “When you have more evaporation, you have less water left over to come down the river.”
Dry soils and thirsty plants also contribute to the problem. When soils are parched by high temperatures in the summer and fall months, it can lead to runoff reductions that persist even a year later, Udall says.
Higher temperatures also mean that the atmosphere is “thirstier” and capable of holding more water. This increases evaporative losses from soils and water bodies.
Over the last year, Udall says we’ve seen how some of these processes can lead to alarmingly low runoff and stream flows.
Baked by high temperatures last fall, soil moisture conditions in November 2020 were far below average across much of the basin.