Under a set of agreements intended to help boost the water level of Lake Mead, which now stands at just 40% capacity, Arizona and Nevada will receive less water from the Colorado River starting next year. The Federal Bureau of Reclamation released projections on Friday showing that Lake Mead, the nation’s largest reservoir, will be at levels next year that continue to trigger moderate cutbacks in both states. Those reductions could eventually increase in the next few years if Lake Mead drops further. The estimates show the reservoir near Las Vegas will likely begin 2021 about 10 feet above a level that would trigger larger cuts.
The Colorado River, which supplies cities and farmland from Wyoming all the way to Southern California, has long been chronically overused and has dwindled during two decades of mostly dry years. The drought has been worsened by higher temperatures unleashed by climate change. The reductions to Arizona and Nevada are part of a 2019 deal called the Lower Basin Drought Contingency Plan, which also calls for California to face cuts if reservoir levels continue to fall. The federal government’s forecast also estimated the levels of Lake Powell along the Arizona-Utah border. That reservoir, the country’s second largest, now sits 50% full. Drought has reduced the amount of water on the Colorado River, draining storage in Lake Mead.
The projections show that Lake Mead, while remaining above an official shortage level, will for a second year be within a zone called “Tier Zero,” which brings the initial cuts in Arizona and Nevada. If the states that rely on the river hadn’t reached the shortage-sharing agreements, the federal government’s data shows that Lake Mead would have dropped significantly lower, said Sarah Porter, director of Arizona State University’s Kyl Center for Water Policy.
“We can see that it has made a big difference,” Porter said. “There’s very little question that without DCP, we’d be in a shortage tier that required cutbacks in water in Arizona that people would have really felt.”
Arizona gets nearly 40% of its water from the Colorado River. The state will again see its water take reduced by 192,000 acre-feet next year, or 6.9% of its total allotment of 2.8 million acre-feet. The cuts are shrinking the amount of water that flows through the Central Arizona Project Canal, reducing deliveries for agriculture and eliminating water for “banking” and groundwater replenishment at facilities along the canal.
Arizona’s state-approved plan for managing the cutbacks involves delivering “mitigation” water to help lessen the blow for some farmers and other entities, while making compensation payments to those that contribute water. Officials have said the state will spend approximately $59 million on the plan, and the Central Arizona Water Conservation District has pledged about $65 million.
Tom Buschatzke, director of the Arizona Department of Water Resources, said the federal government’s projections show that the drought contingency plan is proving successful.
“Its implementation offsets potentially deeper cuts in Arizona’s Colorado River allocation,” Buschatzke said in a statement. His department said entities in Arizona this year are conserving a total of 385,000 acre-feet in the lake.
In one recent study, scientists with the U.S. Geological Survey estimated that warmer temperatures were behind about half of the decline in the river’s flow from 2000-2017. The researchers projected the river could lose about a fourth of its flow by 2050 as global temperatures continue to climb with emissions of greenhouse gases.
“We have been coming to grips with the reality that the watershed produces less water,” said Jack Schmidt, a professor at Utah State University. “The pie keeps shrinking.”
Estimates from the Bureau of Reclamation show the inflow into Lake Powell this year has been one of the lowest years of the past half century.
“This past year was amongst the worst we’ve had, in a year that we had an average snowpack. That’s pretty damn scary,” Schmidt said. “This year is the sort of stuff that makes people very nervous.”
Schmidt is a member of the Colorado River Research Group, a team of scholars who in July published a report discussing efforts to come to terms with “New Hydrologic Realities” along the Colorado River. They said in the report that the 19‐year period from 2000 to 2018 was the driest in the basin since the government began estimating runoff in 1906, and that these years have recently been called a “megadrought.”
“We now know that increasing drying should be expected and that extreme megadroughts seem inevitable,” the researchers wrote. They said they have also seen that “tremendous conservation, cooperative management, and overall ‘belt‐tightening’ is also possible and is much less daunting than the socioeconomic fallout that could accompany empty reservoirs.”
The drought contingency plans for the river’s upper and lower basins, which representatives of seven states signed last year at Hoover Dam, are designed to temporarily reduce risks of reservoirs falling to critically low levels between now and 2026.
Federal officials plan to start a review by the end of this year to examine how the existing rules have worked and how the guidelines for potential shortages, which were last approved in 2007, could be improved after 2026. Arizona water officials held an initial meeting in June to start to outline next steps in talks on the Colorado River.
As the negotiations turn toward new guidelines, and toward how to “share the pain” of a declining water supply, Schmidt said, “we’re almost surely going to have to develop more adaptable, more flexible rules.”
“We have not been in good shape in the 21st century, and so everything needs to be rethought,” he said.
 James Ian. “’The pie keeps shrinking’: Lake Mead’s low level will trigger water cutbacks for Arizona, Nevada” Arizona Republic 15 August 2020, https://www.azcentral.com/story/news/local/arizona-environment/2020/08/15/lake-mead-low-arizona-nevada-water-cutbacks/5584993002/
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