With climate change and prolonged drought continuing to weigh on the Colorado River, the federal government declared a water shortage for the first time on Monday at Lake Mead, one of the river’s main reservoirs.
The declaration triggers cuts in water supplies, primarily affecting farmers in Arizona for the time being. Starting next year, they will be cut off from much of the water they have relied on for decades. Much smaller reductions are required for Nevada and Mexico across the southern border.
But bigger cuts, affecting far more of the 40 million people in the west who depend on the river for at least some of their water supplies, are likely in the years to come as a warming climate continues to decrease how much water flows from rain into the country Colorado flows and snow melts.
“As this seemingly unstoppable decline in supply continues, the bottlenecks that we are beginning to see implemented will only increase,” said Jennifer Pitt, director of the Colorado River program at the National Audubon Society. “Once we’re on that train, it’s not clear where it stops.”
The Bureau of Reclamation, an agency of the Home Office, explained the shortage when it released its latest projections for the river for the next 24 months. That forecast indicated that Lake Mead, the vast reservoir near Las Vegas, would reach 1,066 feet above sea level by the end of this year. It hasn’t seen such a low level since the Hoover Dam was completed in the 1930s. The lake will be 34 percent full.
“Today’s announcement highlights the challenges we face in the Colorado River Basin and elsewhere to the west,” said Tanya Trujillo, assistant secretary of the interior for water and science.
Water levels at Lake Mead and the other major Colorado reservoir, Lake Powell, Utah, have been declining for years, leaving a tell-tale white “bathtub ring” of mineral deposits along the coast as demand has exceeded supply.
The mandatory cuts, known as Tier 1 reductions, are part of a contingency plan that came into being in 2019 after lengthy negotiations between the seven states that use the waters of the Colorado River: California, Nevada and Arizona in the lower basin and New Mexico, Utah , Colorado, and Wyoming in the upper basin. Indian tribes and Mexican officials were also involved in the planning.
The shortage announced on Monday only affects the lower pelvic states, but the Bureau of Reclamation could explain a similar shortage for the upper pelvis, possibly as early as next year.
The explanation of the shortage will reduce Arizona’s supply of water from the Colorado River, which is delivered through a system of canals and pumping stations called the Central Arizona Project, by approximately 20 percent, or 512,000 acre-feet. (An acre-foot is about 325,000 gallons, enough water for two or three households for a year.)
In anticipation of the cuts, some farmers have left fields fallow or switched to less water-intensive crops. Others will pump more groundwater to make up for the cuts, raising additional sustainability issues as groundwater supplies are not unlimited.
“The river is the iconic resource,” said Kevin Moran of the Environmental Defense Fund. “But we also have to think about the management of our groundwater.”
For Lake Mead and Colorado, the question is whether the Tier 1 cuts will be enough to halt the decline in supply as climate change continues to affect the flow of the river. Additional tiers, which could soon come into effect if lake levels continue to drop, as the projects released on Monday released the forecast, would require increasingly draconian cuts. And more cuts may need to be negotiated.
This year was one of the worst for Colorado River runoff, said Ted Cooke, general manager of the Central Arizona Project. “The big question is what will happen in 2022?” He said. After two decades of drought, “one thing we don’t have is the resilience of the reservoirs, because they’re so low to withstand the kind of year we’ve had this year in a row.”
Sharon B. Megdal, director of the Water Resources Research Center at the University of Arizona, said she believed the declaration’s focus on the poor condition of the river would lead to more efforts in the area to use less water. “I think we’ll see some adjustments,” she said. “But I don’t know if we can do that much to avoid further cuts.”
With the various negotiated step cuts, “we’re really only talking until 2025,” said Dr. Megdal. “As things get worse and worse, I think there would be some intervention to do more. We cannot allow the river system to fail. “
Lake Mead now contains approximately 12 million acre-feet of water, well below its nearly 30 million acre-feet capacity. The last time it was almost full was two decades ago.
Since then, much of the Southwest has been in a drought that climate scientists say can rival some long-lasting droughts over the past 2,000 years.
Even in the last year, with occasional good snow cover in the Rocky Mountains, the amount of water that drains into the river has decreased. Researchers say warming is mainly responsible for this because the soils have become so dry that they soak up much of the melting snow like a sponge before it can reach the river.
Planning for the likelihood of lower water supplies in the Colorado River began shortly after the onset of the drought. By 2007, the states had developed guidelines for dealing with bottlenecks, which the 2019 agreement made concrete.
“Today’s announcement is a recognition that the hydrology that was planned years ago and that we hoped we would never see is here,” said Camille Touton, an assistant commissioner for the Bureau of Reclamation.
“The river is in unknown territory,” said Mr. Moran. “Climate scientists have articulated pretty well that about 40 to 60 percent of the decline is due to a warming climate.”
Mr Moran said the new infrastructure bill, which the Senate passed but faces a more rocky road in the House of Representatives, includes at least several billion dollars that could help the region cope with this new reality. This includes funds to improve so-called natural infrastructure, including forests, water catchment areas and underground aquifers, which could help increase supply or at least slow down decline.
“Our water infrastructure doesn’t just consist of artificial reservoirs and sewage treatment plants,” he said. “It’s the natural system too.”
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