Three years ago, state hydrologists in the Colorado River Basin began to do some modeling to see what the future of Lake Mead—the West’s largest reservoir—might look like. If the dry conditions continued, hydrologists believed, elevations in Lake Mead—which is fed by the Colorado River—could drop much faster than previous models predicted.
For decades, the West’s big reservoirs were like a security blanket, says Anne Castle, the former assistant secretary for water and science at the Interior Department. But the blanket is wearing thin. Under normal conditions, Lake Mead loses 1.2 million acre-feet of water every year to evaporation and deliveries to the Lower Basin states plus Mexico; that all amounts to a 12-foot drop. Previously, extra deliveries of water from Lake Powell offset that deficit, but after 16 years of drought and increased water use in the Upper Basin, those extra deliveries are no longer a safe bet.
“There’s a growing recognition that even these huge reservoirs aren’t sufficient to keep the water supply sustainable anymore,” says Castle.
For the three Lower Basin states—California, Arizona and Nevada—that rely heavily on Lake Mead, the situation is particularly urgent. For the last several years, Mead has hovered around 1,075 feet above sea level, the point at which harsh water-rationing measures kicks in. And if conditions in the reservoir continue to worsen, the Interior Department could even take control of water allocation from Lake Mead.
So with the threat of a federal takeover looming, water policy leaders in the Lower Basin states, along with the Bureau of Reclamation, the reservoir’s operator, began meeting last summer to discuss ways they can jointly boost water levels in Lake Mead. Some of the details are now available and indicate that all three states are now willing to accept additional water cuts from the reservoir on top of the cuts that they previously agreed to make in 2007.
Those measures follow a set of federal guidelines adopted nine years ago to manage water deliveries from Lake Mead, given the likelihood of future shortages. The guidelines established a series of thresholds for the reservoir’s water levels that would trigger increasingly severe cutbacks for the Lower Basin states. At the time they were negotiated, few people anticipated that the drought would last as long as it has, but as Lake Mead inched closer to the critical 1,075 mark, water managers in the Lower Basin realized the existing guidelines were not enough to prevent an eventual shortage.
While the terms of the new agreement between California, Arizona and Nevada are still being negotiated, a few details have emerged. For starters, the Bureau of Reclamation has pledged to cut 100,000 acre-feet annually through efficiency measures such as lining irrigation canals to prevent seepage, or possibly by re-opening the long-shuttered Yuma Desalting Plant.
The three states’ willingness to collectively ration their water use would have been unthinkable just a few decades ago, when states fought each other in court to win as much water from the Colorado River. The cooperation is a nod to how new climate realities are re-shaping old water politics in the West. Take California, for instance. Legally, the state could hold on to every drop until Lake Mead is nearly down to mud, since the 1968 law that authorized the Central Arizona Project’s construction gave California the highest priority water rights to the Colorado River. But at that point, says Castle, they’re just as impacted as everyone else.
Other collaborative agreements to reduce the strain on the Colorado River include a 2014 Memorandum of Understanding between the big water providers in the Lower Basin states, the Bureau of Reclamation and the Central Arizona Project, pledging “best efforts” to conserve 40,000 acre feet in Lake Mead. In 2014, major municipal water providers in Arizona, California, Nevada and Colorado also agreed to fund new water conservation projects through a pilot initiative called the Colorado River System Conservation program.
For the Lower Basin especially, the negotiations are necessary to avoid the potential federal takeover, says Tom Buschatzke, the director of the Arizona Department of Water Resources. Although the secretary of the interior, Sally Jewell, has not voiced any immediate plans to that effect, in the past, she has made public statements on the matter.
For Buschatzke, the threat is clear: “She’ll take action if we don’t collaborate,” he says.
Here are the cuts states could face:
Arizona would lose 512,000 acre-feet of its total 2.8 million acre-feet per year allotment if Lake Mead dips below the 1,075 feet threshold. That’s 192,000 acre-feetmore than the 320,000 acre-feet it had previously agreed to cut under the 2007 guidelines. Further cuts occur if the reservoir continues to drop. In another unprecedented move, Arizona water officials are talking about trying to spread cuts across all sectors of the state’s economy that rely on CAP water for drinking and irrigation—cities, farms, industries, Indian tribes and others—instead of letting only farmers take the brunt of the cuts, as dictated by their junior water rights.
California: Thanks to the 1968 law that authorized CAP’s construction, California’s 4.4 million acre feet allotment is shielded from most of the cuts should a shortage on Lake Mead be declared. But as part of the new negotiations, the state has volunteered to cut its water use from Lake Mead by 200,000 acre feet if the reservoir’s levels fall below 1,045 feet, and up to 350,000 acre-feet if levels sink to 1,030 feet.
Nevada: The state with the smallest allotment of Colorado River water, Nevada would take a much smaller share of the cuts—8,000 acre-feet if Mead drops below 1,045 feet, and 10,000 acre-feet after that—because it has the rights to only 300,000 acre-feet.
According to Buschatzke, the three states anticipate finalizing the agreement by early this fall, at which point negotiators will begin working the new measures into law. Those changes in law will likely not happen before 2017.
For Castle, the discussions are part of a new era in water politics—one that looks increasingly collaborative.
“We haven’t seen states versus state or state versus feds for a long time,” she says. “There’s a recognition that litigation is failure—that we need to come together and make things work.”
Sarah Tory is a correspondent for High Country News, where this story originally appeared.