‘Red alert’: #LakeMead falls to record-low level, a milestone in #ColoradoRiver’s crisis — #AZ Central #COriver #aridification

Members of the Colorado River Commission, in Santa Fe in 1922, after signing the Colorado River Compact. From left, W. S. Norviel (Arizona), Delph E. Carpenter (Colorado), Herbert Hoover (Secretary of Commerce and Chairman of Commission), R. E. Caldwell (Utah), Clarence C. Stetson (Executive Secretary of Commission), Stephen B. Davis, Jr. (New Mexico), Frank C. Emerson (Wyoming), W. F. McClure (California), and James G. Scrugham (Nevada)
CREDIT: COLORADO STATE UNIVERSITY WATER RESOURCES ARCHIVE via Aspen Journalism

From AZ Central (Ian James):

Lake Mead has declined to its lowest level since the reservoir was filled in the 1930s following the construction of Hoover Dam, marking a new milestone for the water-starved Colorado River in a downward spiral that shows no sign of letting up…

The lake’s rapid decline has been outpacing projections from just a few months ago. Its surface reached a new low Wednesday night when it dipped past the elevation of 1,071.6 feet, a record set in 2016. But unlike that year, when inflows helped push the lake levels back up, the watershed is now so parched and depleted that Mead is projected to continue dropping next year and into 2023.

Lake Mead, the largest reservoir in the country, now stands at just 36% of full capacity.

In the past month, Mead has already fallen below the official threshold of a shortage, which the federal government is expected to declare in August. That will trigger major cuts in water allotments for Arizona, Nevada and Mexico next year. And even bigger water reductions could be forced upon the Southwest if the reservoir continues to drop, which government estimates show is likely…

The reservoir’s continuing decline, [Felicia] Marcus said, should ring “alarm bells” across the West that the days of business-as-usual approaches are over and that “we need to accelerate everything we can to use less water.”

That includes speeding up efforts that cities and water agencies are already undertaking in parts of the Southwest, such as investing in recycling wastewater, capturing stormwater or cleaning up polluted groundwater, Marcus said. And it also includes promoting conservation and more efficient water use in a variety of ways, she said, from investing in water-saving technologies on farms to offering homeowners cash rebates to removing grass and replacing it with drought-tolerant landscaping.

With shortage measures set to take effect next year, Arizona is in line for the biggest water cutbacks.

That will shrink the amount flowing through the Central Arizona Project Canal to farmlands in Pinal County that produce alfalfa, cotton, wheat and other crops. Farmers in Pinal plan to pump more groundwater from newly drilled wells, but they’ll still be short with the loss of Colorado River water and are planning to leave some farmlands dry and unplanted over the next couple of years.

In a first-level shortage, the water supplies of Arizona’s cities will be spared from cutbacks. But that could change over the next two years if Lake Mead continues to decline.

In the Las Vegas area, people are already conserving enough each year that their water supplier will be able to contribute its portion of the reductions from its unused allocation. But that hasn’t stopped Nevada’s leaders from pushing for more water-savings by getting rid of grass on medians and outside businesses and subdivisions, as required under a newly enacted law that bans “non-functional turf” in the Las Vegas area…

The watershed has been ravaged by one of the driest 22-year periods in centuries. Scientists describe the past two decades as a megadrought worsened by climate change, and say the Colorado River Basin is undergoing “aridification” that will complicate water management for generations to come.

In 2000, Lake Mead was nearly full and its surface was lapping at the spillway gates of the Hoover Dam. Since then, the reservoir has fallen nearly 143 feet. And it’s now at the lowest levels since 1937.

Signing ceremony for the Colorado River upper and lower basin Drought Contingency Plans. Back Row Left to Right: James Eklund (CO), John D’Antonio (NM), Pat Tyrell (WY), Eric Melis (UT), Tom Buschatzke (AZ), Peter Nelson (CA), John Entsminger (NV), Front Row: Brenda Burman (US), and from DOI – Assistant Secretary of Water and Science Tim Petty. Photo credit: Colorado River Water Users Association

Two years ago, representatives of the seven states that depend on the Colorado River met at Hoover Dam to sign a set of agreements called the Drought Contingency Plan, which laid out measures to take less water and share in reductions during a shortage to reduce the risks of Lake Mead falling to critically low levels.

But the declines have continued and the drought has intensified over the past year, with much of the watershed baking through the driest 12 months in 126 years of records. The river and its tributaries have dwindled, shrinking the flow into Lake Powell at the Utah-Arizona border, and in turn driving the receding water levels at Lake Mead…

Arizona’s plan for managing the shortages involves deliveries of “mitigation” water to help temporarily lessen the blow for some farmers and other entities, as well as payments for those that contribute water. The state and CAP approved more than $100 million for these payments, with much of the funds going to the Colorado River Indian Tribes and the Gila River Indian Community for water they contributed…

At full pool, Lake Mead is the largest reservoir in the United States by volume, but two decades of drought have dramatically dropped the water level behind Hoover Dam as can be seen in this photo. (Source: U.S. Bureau of Reclamation)

Over the past year, the declines in water levels have accelerated, outpacing previous estimates due to extremely parched conditions across the watershed in the Rocky Mountains, where much of the river’s flow originates as melting snow. Hotter temperatures have made the whole watershed “thirstier,” as climate researchers put it, eroding the flow of the river as vegetation draws more water and as more moisture evaporates off the landscape…

In just 12 months, the [Lake Mead’s] level has dropped nearly 20 vertical feet…

Officials from Arizona, Nevada, California and Mexico have been talking about other ways they might work together on long-term projects to shore up water supplies. One idea they’re studying would be for Arizona to work with Mexico to build a desalination plant on the shore of the Sea of Cortez and trade some of the drinking water that’s produced for a portion of Mexico’s Colorado River water.

Officials from Las Vegas’ Southern Nevada Water Authority have offered to invest in a water recycling project in Southern California, which would enable the agency to use some of the Metropolitan Water District’s Colorado River water in exchange. Arizona water officials are also considering joining the other agencies and taking part in the project.

When representatives of the seven states signed the Drought Contingency Plan on a terrace overlooking Hoover Dam in 2019, some of them described the deal as a “bridge” solution to temporarily lessen the risks of a damaging crash and buy time through 2026, by which time new rules for sharing shortages would be negotiated and adopted.

The agreement establishes a series of progressively larger water cutbacks if Lake Mead continues to drop below lower trigger points in the coming years.

If the reservoir drops about 26 more feet to below elevation 1,045 feet, California would start to take cuts.

And if the water level falls below 1,025 feet, which is a scenario the deal aims to avoid, the largest reductions would take effect for all three states and Mexico.

Increasingly, some researchers are voicing concerns that even the major cuts contemplated in the deal might not be enough. Some have suggested that with extremely dry conditions persisting in the watershed, the region’s water managers might need to take bigger steps before 2026 to prevent Mead’s levels from continuing to plummet.

Climate change is causing the Southwest to aridify. (Left) Since the 1930s, increasing temperatures have caused the percentage of precipitation going to evapotranspiration (ET) to increase at the expense of precipitation going to Colorado River flow, resulting in an unprecedented and still ongoing megadrought (shading) starting in 1999 (8). (Right) Higher temperatures have already reduced Colorado River flow by 13%, and projected additional warming, assuming continued high emissions of greenhouse gases, will increase ET while reducing river flow even more through the 21st century. Data on Left are 20-y running means from ref. 5, and data on Right are calculated from Representative Concentration Pathways (RCP) 8.5 multimodel Coupled Model Intercomparison Project–Phase 5 (CMIP5) ensemble temperature increases projected for the Upper Colorado River Basin combined with temperature sensitivity of −9.3%/°C estimated by ref. 5, assuming no change in precipitation.

“We really have seen this coming all along on some level,” said Brad Udall, a water and climate scientist at Colorado State University. “And we in some ways aren’t ready for it, despite all the things we’ve done to make us feel good that we were ready for it.”

Udall said the network of people who work on Colorado River issues have made great strides in collaborating on adaptation strategies, including through the 2019 deal. But he said he’s not convinced that adequate measures are in place to quickly scale up the more aggressive steps if the contemplated cuts turn out to be insufficient — other than the possibility that Interior Secretary Deb Haaland could convene the states’ representatives and determine what steps to take, which is also included as a sort of backstop measure in the deal.

“This thing could spiral out of control pretty quickly,” Udall said, if more years of severe drought desiccate the region as they did in the early 2000s.

He said he also worries about the fact that some of the water in Lake Mead is reserved for specific water users based on prior conservation, which has been encouraged under the deal and previous agreements.

Concerns about that banked water also have been voiced by others, including Margaret Garcia, an assistant professor at Arizona State University who focuses on water infrastructure and management. She said this system of banking water, technically called “intentionally created surplus,” poses concerns because it means some water in Mead is already spoken for beyond established allocations, and this stored water can still be withdrawn unless the reservoir hits critical lows.

As Garcia put it, “a savings account full with IOUs is not the same as a full savings account.” And Lake Mead’s account is far from full.

The heart of the issue, Udall said, may be developing new ways of quickly adapting to a river that’s yielding less water as the West grows hotter and drier.

“We may need to take this next big step, which is how do you permanently reduce demands?” Udall said.

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