Crisis on the Colorado: New Analysis Charts Hard Choices for a Drying River

It’s time for a serious reckoning with the way we use water from the Colorado River, and the way forward will be tough, according to a new publication by Jack Schmidt, chair of the Center for Colorado River Studies in the Quinney College of Natural Resources, Charles Yackulic of the USGS Grand Canyon Monitoring and Research Center, and Eric Kuhn, retired general manager of the Colorado River Water Conservation District.

The article, published recently in WIREs Water, takes a new look at the development and future of the Colorado River crisis. Schmidt and colleagues make a critical distinction between the ultimate and proximate causes of the crisis — although the roots lie in trends for declining watershed runoff in a warming world, the immediate cause is closely tied to society’s inability to adaptively respond to the declining runoff for the past 20 years and more.

The authors show that Lake Powell and Lake Mead, the two largest reservoirs in the United States, lost nearly half their total water storage between 2000 and 2004, and that policy changes implemented thereafter did not result in any significant recovery of reservoir storage. So when the next period of unusually low runoff occurred (2020-2022), the reservoirs were almost drained to the point where hydroelectricity could no longer be produced.

Despite an extraordinarily wet year in 2023, the reservoirs of the Colorado River basin remain critically low. Basin-wide water use must be significantly reduced to match the available supply and to allow some recovery in reservoir storage, they said.

Although it is easy to articulate the general principle that use must match supply, it is harder to precisely define the magnitude of what reduction is needed, the authors write.

“Assuming persistence of conditions like those of the past 20 years, water use would have to be reduced by 1.5 million acre feet per year to match supply, but an additional 1 million acre feet per year of reduction would be needed to recover lost reservoir storage,” they said.

For context, over the last 20 years the entire river system has averaged a runoff of 13.6 million acre feet per year (about 13% less than conditions of the mid- and late 20th century), but water consumption has averaged around 15 million acre feet per year.

Such deep cuts are a seemingly impossible ask to many, but the Colorado River can’t provide a sustainable water supply unless consumptive use is reduced to match the declining supply, Schmidt said. To stabilize the reservoirs, basin-wide use would have to be reduced to 13-20% less than the average use this century. Refilling the reservoirs would require even deeper cuts.

Water from the Colorado River is important in the region. In the Upper Basin (Utah, Colorado and Wyoming), it is used in the agricultural valleys of western Colorado and southwestern Wyoming, the Uinta Basin and Castle Valley of Utah, and the San Juan River valley of New Mexico. Municipal users are primarily supplied by trans-basin diversions outside of the Basin between Cheyenne and Pueblo, and in the Salt Lake and Utah Lake valleys, and in the Rio Grande valley of New Mexico.

Water users in the Lower Basin (California, Arizona, New Mexico) and Mexico include districts along the Lower River and a large part of the former Colorado River delta near Yuma and in the Coachella, Imperial, and Mexicali Valleys. Some of Mexico's allocation of Colorado River water is transferred out of the Basin to Tijuana and Ensenada. Some of California's allocation is transferred out of the Basin to municipal users in Los Angeles, San Diego, and surrounding areas. U.S. metropolitan areas within the Basin that are served by the river include Phoenix, Tucson, and Las Vegas.

The largest water use occurs in California, and this amount was almost as much as the total consumed in the Upper Basin. The primary user of water in the Upper Basin is agriculture (58% of the Upper Basin total). Reservoir evaporation (20%), trans-basin diversions out of the Basin (17%), and by municipalities and industry (6%) also draw down significant portions of the Upper Basin’s allotment.

Since the storage buffer at the reservoirs is now largely gone, and the exceptional runoff from 2023 will not refill them (it would take four to five additional unusually wet years in succession to refill Lake Powell and Lake Mead if basin-wide water use remains unchanged), water-supply allocation will need to be adapted to future conditions, which will likely be increasingly dry. And rehabilitation of dewatered ecosystems in the Colorado River Delta and in some Upper Basin tributaries will require continued commitment among users to protect existing environmental flows and to acquire additional water for the environment of an overallocated system, the authors said.

Schmidt will present this analysis, other considerations for the river and potential for change at an upcoming Research Landscapes event on Aug. 10 in Salt Lake City.