A cool map for a warming watershed arrives at the right moment.

By Lisa Owens Viani

As the western United States continues to wither in an extended drought, the Colorado River’s two largest reservoirs, Lake Mead and Lake Powell, have fallen to their lowest levels since they were first filled—Lake Mead in 1935 and Lake Powell in 1963—according to John Fleck, a professor of practice in water policy and governance in the Department of Economics and director of the Water Resources Program at the University of New Mexico, Albuquerque. Against this parched backdrop, the Babbitt Center for Land and Water Policy has published a timely new map of the Colorado River watershed that illuminates the complicated issues facing basin managers now and in the future as water becomes an ever more scarce and precious commodity in the West.

Produced in partnership with the Lincoln Institute of Land Policy’s newly launched Center for Geospatial Solutions, the peer-reviewed map, which includes photographs and extensive narrative, tells the story of the river’s complicated legal and political history and challenges.

Often called the hardest-working river in the West, the Colorado supplies seven states and more than 40 million people with water, flowing 1,450 miles from its headwaters in the Rockies to (at least historically) the Gulf of California. Although the watershed is legally divided into upper (Colorado, Wyoming, New Mexico, and Utah) and lower (California, Arizona, Nevada) basins, the map outlines the entire watershed as one basin, including areas that rarely, if ever, receive flow from the river, such as the Salton Sea in Southern California and the Laguna Salada in Mexico. Inset maps focus on wildfire risk, the river’s delta in Mexico, the Salton Sea, and the connections between water management in cities and agriculture. Photos highlight the river’s headwaters and delta, reservoirs, and California’s Imperial Valley, which receives about three inches of rain per year and depends on the river to irrigate a half million acres of lettuce and other winter vegetables.

Over the two years it took to complete the map, a team of five—a cartographer, a GIS analyst, two water policy experts, and a writer—consulted with an array of experts and stakeholders, including scientists, water managers, agricultural users, Native American tribes, and others. “We really tried to strike a balance with peer review [and] making sure we had our facts straight,” says Zachary Sugg, a senior program manager with the Babbitt Center. “But we also wanted to preserve our voice as an organization. We had a lot of past work to draw from and could pick and choose what we liked about previous maps, both positive and negative examples.”

The river has a long and complicated legal history. The map’s narrative grounds readers in that background, explaining how the 1922 Colorado River Compact and later legal agreements, including a 1944 treaty with Mexico, divided the river’s water between the United States and Mexico—with the upper basin in the United States receiving 7.5 million acre-feet, the lower U.S. basin 7.5, and the remaining 1.5 million acre-feet to Mexico. The compact, upon which the Law of the River that governs all river users is based, was flawed in its hydrologic assumptions, with the river’s long-term average annual flow as later determined by tree-ring analysis—14.3 million acre-feet—far less than the 16.5 million acre-feet allotted to water users in 1922.

“We’ve finally grown into the full allocations; we’re finally trying to use all of the water, which is more than the river could ever supply,” says Fleck, who was involved in early discussions about the map. “It’s important across the basin to think about this as a shared system because the challenges are shared,” he says. “When you’re using Colorado River water, it’s easy to get wrapped up in your little piece of it.”

While the map may ultimately be used by decision makers as a new round of negotiations over how to manage the drought-stricken river begins, Sugg says the center’s goal was to design it for a broad audience to help the public see the big picture and understand the issues that drive negotiations over water use in the basin. “We wanted the map to convey the magnitude and importance of those decisions—how many people, places, and things their decisions impact,” Sugg says. The map adds to an online Story Map the center completed in 2020, which includes a timeline of the river’s cultural and legal history over the past three centuries. “We’re hoping the maps correct some of the misperceptions that people may have—basic facts about where the basin is, where the water goes both naturally and where it leaves the basin through canals and pipelines.”

The new map was also designed to respond to complaints about earlier maps of the watershed, says Sugg, whose team pored over them. “The river basin is binational, and a lot of American-made maps showed the basin stopping at the border or had a huge array of representations of where the boundaries of the basin were in Mexico,” he explains. Parts of Southern California were also left out in previous maps, particularly the Salton Sea. “That’s an area that for management purposes is outside the basin because it is no longer hydrologically connected to the main stem of the Colorado River,” Sugg says. “But people pointed out that that’s an area that had been part of the delta of the river for thousands and thousands of years and only stopped becoming part of the delta because of the dams built on the main stem in the 20th century. Ditto the Laguna Salada Basin just to the south in Mexico.” Over the past thousand years, the river would change its course and sometimes empty into the Salton Sea, which was then part of a dynamic wetlands complex that extended into Mexico. The Great Divide Basin, at the northern end of the watershed in Wyoming, was also included in the new map although it has been hydrologically disconnected from the river for millennia.

Transbasin diversions and canals that export water to other areas are shown on the map and described in the narrative. Says John Berggren, a water policy analyst with Western Resource Advocates, “A lot of people don’t understand water and watersheds, especially in the Colorado River Basin where water is moved out of the actual hydrological basin to farms and cities throughout the West. People just generally don’t understand that or how the West is fundamentally connected through water. This map shows in one place how we’re all connected by this river.”

Berggren says one of his hopes for the map is that it will inspire people, particularly landscape architects, to think about how designing and advocating for more water-efficient landscapes in urban areas could have a positive ripple effect throughout the basin. “Landscaping decisions we make here in the front range of Colorado can impact the river downstream,” Berggren says. “How we design our landscapes has huge implications for the river. There’s starting to be a shift away from nonessential turf. Turf is really dumb when water is so precious.” In response to the threat the drought is posing to the river, which is one of Nevada’s main sources of water, in June the state took the unprecedented step of banning nonfunctional turf (grass that is not being used for a purpose and is merely decorative). Berggren wants to see more xeric, native, low-water landscapes in lieu of turf throughout the watershed. “Those are what our landscapes should look like,” he says. “We need to engage people from the get-go—if they are done in a thoughtful, water-efficient way, we can build a culture where bluegrass is no longer the default but instead [we can] have climate-appropriate native landscapes that still look beautiful.”

Nancy Wilkinson, a professor of geography and environment at San Francisco State University, who specializes in water resources in the West, appreciates the way the map shows the enormous scale of the Colorado River Basin. “It helps us see it in its international entirety as a profoundly complicated, challenging, and important management tool with many moving parts,” Wilkinson says. She suggests two improvements for any future iterations. “I wish the map used bolder lines for out-of-basin water exports to Southern California. These transfers account for a tremendous draw on the river’s dwindling waters and have prevented the river from reaching the Gulf of California for many decades.” She would also like to see even more information about climate on the map. “I might also wish to see [more about] the spectacularly high evaporation rates from the reservoirs and the equally stunning evapotranspiration rates from the agricultural fields the river irrigates. A few well-placed water budget climographs could speak volumes.”

The map team deliberated over how much information about the ongoing drought and water shortages to include. “We considered whether writing about very current events would limit the life span or viability of the map but felt like the drought and the allocation problems were too important to not point to,” Sugg says.

Another important feature on the new map is that it shows the territories of the 30 federally recognized Native American tribes that hold water rights to the river but have historically been unable to participate in negotiations or to access the full amount of their water. Matt McKinney, a cochair of the Natural Resources Conflict Resolution Program at the University of Montana, and cofacilitator of the Water and Tribes Initiative, and Daryl Vigil, a cofacilitator of the Water and Tribes Initiative, advocated for including the territories. “It is the most inclusive of all of the maps, including federal maps, showing all federally recognized tribes. It’s a huge step forward,” McKinney says. They plan to use the map as they work to get a stronger voice at the negotiating table.

Perhaps most critically, the map highlights the need for greater cooperation among all river users, with the drought predicted to continue this year and possibly longer, and with climate change causing significant streamflow losses in the river. Although snowpack in the basin was 80 percent of average this year, the river’s flow was less than 30 percent of average because hot dry summers bake the soils, reducing flows the following year, Fleck says.

Printed maps are available upon request from the Babbitt Center’s website, as are free pdf downloads. “We hope the Colorado Basin map and Story Map together will help to educate the public and interested individuals about the shortage sharing and the Colorado River management negotiations so they can get engaged in supporting sustainable water and land management,” Sugg says.

Lisa Owens Viani is a contributing editor to the magazine who lives in Northern California and is intimately acquainted with drought in the West.