A Hot Drought
The Southwest has always been subject to dry spells. But something’s changed.
Less rain and snow coupled with higher temperatures have created a "hot drought" in the Colorado River basin.
Falling water levels at the major reservoirs of Lake Mead and Lake Powell are alarming visual symptoms of an ailing Colorado River’s diminished flows. One of the major causes of the river’s reduced flow is changing climate conditions that have prevailed since the year 2000 in the Colorado basin.
Brad Udall, Senior Climate and Water Research Scientist and Scholar at Colorado State University’s Colorado Water Institute, has been studying the Colorado River for decades, and boasts an extensive knowledge of the river’s changing conditions. “In an odd way I’ve been studying the river since I was 15 years old,” he says. At this young age, Udall went on a river trip with his mother, and became fascinated by the river and its history. Udall worked on the river as an engineer in the 1980s, and later ran a climate program at the University of Colorado before coming to CSU.
Udall explains that climate is driving the Colorado River drought through two different mechanisms: reduced precipitation and increased temperature. “Historically, drought has been caused by lack of precipitation,” he says. “In a climate change world, high temperatures can cause drought too, and can exacerbate what would otherwise be minor drought and make it major drought.”
A reduction in rain and snow has occurred throughout the Southwest in recent decades, and accounts for roughly two-thirds of the documented 19 percent decrease in Colorado River flows from 2000-2014. Winter snowpacks have been smaller in the Rocky Mountains, the headwaters of the Colorado. That results in less immediate spring and summer meltwater to replenish the river, and in diminished groundwater storage that feeds the river over longer timescales. Below-average rainfall in the spring and summer further reduces the water entering the system.
But the Colorado’s contemporary precipitation drought has been relatively minor. Unlike other recent droughts in the Southwest, the Colorado River basin drought is unique because about a third of the overall water loss is associated solely with hotter temperatures caused by global warming, turning an otherwise “modest drought into a major big deal,” according to Udall. The average annual temperature in the Upper Colorado River Basin was nearly 1 degree Celsius, or 1.8 degrees Fahrenheit, warmer from 2000 through 2014 than the average for the previous century. These warmer temperatures result in higher rates of water loss through evaporation from the Colorado River, especially its reservoirs.
The imperiled Colorado River flows have raised questions about the future: how bad will our water shortage become due to continued global warming? This question is a challenging one to tackle because climate models often have a lot of uncertainty when it comes to projected changes in precipitation; snow and rainfall are strongly influenced by large-scale patterns of variability across entire oceans that are difficult to forecast.
But climate models are much more reliable when it comes to projecting changes in temperature. Because we know that water reductions in the Colorado River Basin are caused partially by temperature increases alone, we can say with certainty that these losses will become more severe. Models suggest that Colorado River flows will decrease anywhere from 11 to 55 percent by the end of the century. Where the basin lands on that scale depends on how much river flows continue to be affected by temperature increases, and how much we reduce our greenhouse gas emissions—both of which are unknown.
But Udall remains optimistic that tangible solutions remain. Because 80 percent of Colorado River water use is associated with agriculture, changes in this industry are an essential part of the picture. “Water conservation in the general sense means cutting down the water that a crop transpires, which by nature means you’ll reduce yield,” he says. “How you get agriculture to reduce is a big part of the story. And cities are going to have to continue to conserve, and conserve, and conserve.”
Dividing a Lifeline
Splitting up the Colorado River’s water has never been easy. It’s only going to become more of a challenge as the climate warms.
Inhabitants of the southwestern United States and northern Mexico have always relied on the lifeline of the Colorado River. The river’s watershed encompasses portions of seven U.S. states (Wyoming, Colorado, Utah, New Mexico, Arizona, Nevada, and California) and two states in Mexico (Sonora and Baja California). As populations in these states boomed in the late 19th and early 20th centuries, how to divide the river’s water fairly became a contentious question. Stakeholders feared the possibility of water shortages due to overuse, particularly because California early on began diverting large amounts of the river’s water to support its growing cities and agricultural industries.
These concerns gave rise to the Colorado River Compact of 1922, negotiated by the seven U.S. states and Congress. It gave the federal government control over future conflicts regarding state-level water use. The compact also established an important dividing line in the river’s watershed, separating the “Upper Basin” (Colorado, Utah, Wyoming, New Mexico, and parts of Arizona) from the “Lower Basin” (most of Arizona, Nevada, and California). Each basin was permitted to withdraw 7.5 million acre-feet from the river each year, but no allocations were made at the level of individual states. (An acre-foot is a common unit for describing volumes of water, enough to cover an acre of land in one foot of water—or enough for one or two typical American households for a year.)
Not everyone was happy. The compact didn’t mention an allocation for Mexico, which didn’t receive a formally agreed-upon allocation until 1944, when the U.S.-Mexico Water Treaty required the U.S. to its neighbor with 1.5 maf of water a year. Arizona refused to agree to the compact until 1944, when it proposed to divert water to its major population centers, Phoenix and Tucson, over California’s objections. The Supreme Court eventually ruled in Arizona’s favor, resulting in the construction of the Central Arizona Project, the system of canals that distributes Colorado River water throughout the state.
In a region of unpredictable precipitation, delivering the precise allocations agreed upon by law requires huge reservoirs that store the river’s fluctuating flows. The construction and regulation of Glen Canyon Dam at Lake Powell (Upper Basin) and Hoover Dam at Lake Mead (Lower Basin) have been key in maintaining water deliveries to states, allowing multiple years worth of Colorado River water to be stored and distributed regardless of above- or below-average flows.
Unfortunately, there’s a key problem, namely that the Colorado River Compact was based on an annual flow of 15 million acre-feet. That was believed to be the river’s average flow in the early 20th century, but that happened to be an unusually wet period. Even before the modern era of climate change, the river was over-allocated. As the river likely diminishes in hotter and drier years ahead, the challenges of allocating its water fairly are the one thing that’s likely to grow.
Water and Mud
Any lake in the desert is a magnet, but dropping water levels on Lake Mead have changed the recreational experience for boaters, and caused headaches for the Park Service.
For decades, tourists and adventure-seekers have flocked to the Grand Canyon, Lake Powell, and Lake Mead to experience the stunning natural beauty of the canyon country and the pleasure of liquid recreation in an arid region. One favorite activity is the surreal reality of floating on water in the desert, either by boating on Lake Mead or rafting down the Colorado River through the Grand Canyon. However, the Colorado’s declining flows have had significant impacts for those plying its waters.
As of June 2019, Lake Mead was only 41 percent full, with its water level more than 125 feet lower than maximum—the lowest level since the reservoir was first filled in the 1930s. That’s caused the closure of three marinas that now stand high and dry. The National Park Service, which manages Lake Mead National Recreation Area, has spent more than $40 million over about the last 20 years extending launch ramps, building new roads, and making other changes to adapt to the lowered water level.
But Lake Mead boaters aren’t alone in having their activities hampered by the Colorado’s vanishing waters. Further upstream, river runners and rafting companies have also had to negotiate changing conditions for Colorado River trips through the Grand Canyon, another cornerstone of tourism in the Southwest. Lake Mead is the location where many Colorado River trips conclude. Guides must safely get their guests off the river and onto dry land, and must pay close attention to the status of “take-out” points where guests disembark their boats and leave the river. Some of these previously reliable take-outs are now inaccessible because Lake Mead’s level has dropped so far.
“We always used to take out at the boat ramp at Pearce Ferry in Lake Mead, but the water level dropped too low starting around year 2000,” says Andre Potochnik, a geologist and river guide who has worked in Grand Canyon since 1973. “Starting then, we either needed to take out before Pearce Ferry or go another 12 to 14 miles to South Cove. Now, a new boat ramp and road have been extended across the silt beds to Pearce Ferry.”
The dropping water level has also caused the formation of new, dangerous rapids. The reservoir’s disappearing water exposes soft sediments, or “silt beds,” that were previously undisturbed under still, deep water. The river flows farther downstream as the reservoir level drops, and its moving water can cut through the silt, eroding it to bedrock and creating hazardous new rapids. “The river has started establishing itself in the deltaic portion of the reservoir,” he says. “Now there’s Pearce Rapid to navigate, which is pretty much a death trap. Fortunately, the new boat ramp allows us to avoid it.”
Boating through the Grand Canyon and on Lake Mead is big business, and that’s not going to change anytime soon. But boaters are going to have to continue to adapt. In late 2018 the Park Service announced a new $25 million plan for further changing Lake Mead’s recreation infrastructure to deal with even lower water levels in the future.
Moving water from the Colorado River into central Arizona was a remarkable — and expensive — engineering feat. But the Central Arizona Project may be less permanent than its planners hoped.
Despite holding water rights on paper after it agreed to the Colorado River Compact, Arizona had no way of using most of its Colorado River allotment in the mid-20th century. The river was largely tucked away in deep canyons as it flowed through northern Arizona, and few people lived or farmed along the lower Colorado. The state’s booming cities, suburbs, and agricultural areas were hundreds of miles away, around Phoenix and Tucson. Delivering river water there was the fundamental reason for the construction of the Central Arizona Project.
In 1968, President Lyndon B. Johnson authorized the Colorado River Basin Project, a giant federal initiative that included the construction of the CAP. It took twenty years to complete construction of the project’s canals and pump stations, at a cost of more than $4 billion, which would equal almost $25 billion in today’s dollars. The end result was 336 miles of canals, tunnels, and reservoirs that move water from Lake Havasu into dry central and southern Arizona. The water is moved through mountains with the help of 13 pumping stations, which together life the water higher than the Empire State Building. The electricity needed to operate those pumps could power about a quarter-million of the state’s houses.
Since its completion in the late 1980s the CAP has seemed a permanent fixture of Arizona, its 80-foot-wide canals crossing highways and linking open desert, fields, and suburban neighborhoods. And Colorado River water has indeed come to be a mainstay of the state’s economy, as 1.5 million acre-feet are annually distributed to farmers, municipalities, and Native American tribes through an elaborate network of canals, laterals, and ditches that are governed by an even more complex system of legal and regulatory agreements.
Many farmers have come to rely on CAP water to irrigate their crops and reduce dependence on expensive and declining groundwater. But as Lake Mead declines it’s that use of irrigation water that is most threatened. In response, farmers are likely to have to go back to groundwater again, if they can afford it, or cultivate less land.
How to split up a diminishing pie? Only three decades after the CAP’s completion, water planners have to contemplate how to manage shrinking deliveries.
Approved in early 2019, Arizona’s new Drought Contingency Plan (DCP) is a response to a reality that no one wants to see, namely the likelihood of impending water shortages on the lower Colorado River. As Lake Mead’s water levels have dropped in recent years, the federal government has told states in the region that they need to prepare for potential cuts in water deliveries. Those cuts may come as early as 2020, though a wet winter in 2018-2019 provided some respite.
Arizona’s response is the DCP, which spells out a series of cutbacks that water users need to plan for over the next seven years. The cutbacks would be triggered by a reservoir water level of 1,075 feet—more than 150 feet below the reservoir’s maximum level, and about a dozen feet below the water level in June 2019.
If the reservoir drops to that level, CAP deliveries would be cut by about a third. Most of the immediate burden would be borne by farmers, especially in Pinal County. They’d have to give up most of their CAP water — about 150,000 acre-feet right away, and approximately another 100,000 acre-feet three years later.
Cuts to municipalities would be much more muted, and probably not noticed by consumers. But if the reservoir keeps dropping to 1,025 feet, further cutbacks would be instituted.
Sarah Porter, the Director of the Kyl Center for Water Policy at Arizona State University, sees the DCP as a necessary first step toward lessening the state’s reliance on a water supply that might not be here forever. “The worry is that the levels of Lake Mead would fall very precipitously,” she explains. The biggest goal of the DCP “is to avoid getting into that very frightening and potentially dramatic situation.” From there, Porter explains that the DCP is designed to “keep the high-priority users — and most specifically cities — out of a serious shortage situation.”
Porter says that fairness that this was an important consideration during the crafting of the DCP. “Mitigation needed to be fair for all water users,” she says. “We weren’t going to treat one class of water users as special over another, so that became an important guiding principle.”
But despite these efforts to serve the interests of diverse stakeholders, the Drought Contingency Plan has been met with resistance. “There are people who have been grumbling about it,” Porter says. Some members of the environmental community, for instance, felt that the plan does not adequately support conservation, while farmers objected that they are being asked to sacrifice too much. But Porter says she’s impressed by what she sees as a change of perspective from earlier, water-wasting ways. “We’re getting away from ‘it’s my right’ to ‘how do we make sure we get what we need?’ And that’s a big shift,” she says. “It’s really an interesting big shift that has taken years to come to pass, but it’s definitely in place. I like to say that nobody likes the plan, but everybody can live with the plan.”
Faced with the likelihood of diminishing CAP deliveries, desert farmers have an unsavory choice — farm less land, or go back to using expensive groundwater at a high ecological cost.
The state’s Drought Contingency Plan attempts to spread the pain of future water shortages, but those who will pay the biggest price upfront are farmers in Pinal County. They hold the lowest-priority Colorado River water rights among Arizona users, so their usage will be cut back as soon as CAP deliveries are trimmed.
Tiffany Shedd of Eloy is one of those farmers. “I farm with my husband,” she says, “farmed for 30 years, and he’s actually a fourth-generation farmer. His family came out around 1913 to this area as land developers, and ended up farming.”
The Shedds use CAP water to irrigate their fields, which primarily raise cotton and wheat. They’ve already had to cut back some, and are anticipating more if Lake Mead continues to fall.
“We’re going to have to fallow about 60 acres in order to have enough water to farm the rest,” Shedd says. “There’s going to be just flat out less water.”
Farmers do have an alternative — groundwater. The DCP provides funding with which farmers can make the switch from river water to pumped groundwater. But pumping is expensive, and there’s not enough funding to replace all of farmers’ CAP water. Nor is groundwater pumping a harmless activity. Before the CAP was completed Pinal County farmers used a lot of groundwater, causing the subsidence of large tracts of land and the abandonment of some farmland as water levels dropped. The resulting bare ground has been slow to revegetate, and every summer serves as a source for large dust storms that roll into the Phoenix area.
Despite these challenges, Shedd bristles at any implication that the deserts of central and southern Arizona are odd places for farming. “It’s an amazing place to grow things, and we don’t have the natural disasters that the rest of the country has,” she says. She questions what she sees as a decision to withdraw CAP water from agriculture while maintaining cities’ and developers’ ability to expand municipal and residential areas. “You can’t just take from your neighbor. We’ve got to be looking at how we can have robust industrial, municipal, mining, agriculture — all of those things are good to have in a state; we shouldn’t be excluding any of them for one. I’m not against growth at all, believe me, but I just think we need to keep our eye on our natural resources while growing.”
Overall, though, Shedd is supportive of what she sees as a strong degree of collaboration that went into the DCP. “One thing we do not want to lose is having all of the stakeholders at the table — you can call it collaboration, you can call it a barroom brawl, I don’t really care — but I think that when you have all of those parties, and they’re kind of fighting for their turf, we end up with the best policy and the best vehicle to get that policy.”