Colorado River Structural Deficit

Colorado River Structural Deficit

Credit: Jeff Lee

Levels at Lake Mead are rapidly dropping, in part, because the water stored in this reservoir is over allocated to the states that share it. This puts the stability of the Colorado River system and reliability of Arizona’s Colorado River supplies at serious risk.

The Issue

Colorado River Structural Deficit

Structural Deficit Infographic

Less water flows into Lake Mead than is taken from it— about 1.2 million acre-feet less annually. The result is a “structural deficit” that causes Lake Mead’s elevation to drop about 12 feet every year, drought or no drought.

Credit: CAP

Lake Mead is the largest reservoir in the United States and a key component of the Colorado River system. It is the reservoir level of Mead that determines shortage conditions on the Colorado River. The lake supplies water to three states and Mexico, serving 20 million people and supporting extensive agriculture.  Water from the lake accounts for 34 percent of the supply portfolio of the AMWUA members. 

The Colorado River is over-allocated. More water is committed to the states and Mexico that rely on the river than is actually available in an average year. In years with normal inflows, Lake Mead declines twelve feet in elevation.  This imbalance between inflows and diversions is known as the “structural deficit.” Eighteen years of drought have exacerbated the problem, hastening the decline of Lake Mead. 

Water managers are well aware of the deficit and have planned for shortages. In 2007, the seven states that share the river, the federal government, and Mexico agreed to interim guidelines that determine how Lake Powell and Lake Mead are managed and how shortages of supplies will be shared. Since that time, it has become clear that there is increasing probability of deeper shortages, sooner, and there is an unacceptable risk of catastrophic declines in Lake Mead. 

System Conservation

Innovative system conservation programs have helped avoid shortages to date and have bought precious time to develop more comprehensive solutions.

The Pilot System Conservation Program, a cooperative effort between Upper and Lower Basin water users, has demonstrated the viability of jointly funding cooperative, voluntary projects to conserve water to increase storage levels in Lake Mead and Lake Powell. The fact that the water saved through the program remains in the Colorado River system and is not allocated to any state, agency, or water user is unprecedented. 

A Memorandum of Understanding (MOU) signed in 2014 enabled a new approach to reduce the risk of shortage. The agreement between the Bureau of Reclamation, Arizona Department of Water Resources (ADWR), Central Arizona Water Conservation District (CAWCD), Metropolitan Water District of Southern California, Southern Nevada Water Authority, Colorado River Board of California and Colorado River Commission of Nevada, identifies voluntary actions to develop from 1.5 to 3 million acre-feet of new water for Lake Mead by the end of 2019.  CAWCD's goal is to store 345,000 acre-feet of water – or approximately four feet of elevation – in Lake Mead between 2014 and 2017. The combined benefit of this agreement may result in a 10-foot elevation boost to the lake.

Drought Contingency Planning

Over the course of the past several years, the seven Colorado River Basin states, the federal government, and Mexico have developed a proposal that would significantly reduce the likelihood of Lake Mead dropping to critical levels and improve the reliability of the river system.  The Drought Contingency Plan (DCP) proposes sharing reductions among Arizona, California, Nevada and the United States, while still honoring previous agreements.   The reductions to Arizona’s and Nevada’s Colorado River supplies will be earlier and deeper than those agreed to in 2007.  Under this plan, California, for the first time ever, would agree to take reductions in Colorado River deliveries if Lake Mead drops to specified elevations.

There is consensus among the parties as well as the broader water community that additional action is necessary. DCP is the next step in protecting the Colorado River system and will serve as a bridge to a future where Western States adapt to reduced supplies.

Colorado River Structural Deficit

Testifying before the U.S. Senate Subcommittee on Energy and Natural Resources, ADWR Director Buschatzke stated, “Collaboration and an all-hands-on-deck approach is the future of the Colorado River.” Credit: Ben Moffat/Cronkite News

Current Efforts

Arizona took an important step on January 31 to protect its Colorado River water and maintain control of its future when the Governor signed legislation approving the State’s participation in the Lower Basin Drought Contingency Plan (DCP). In doing so, Arizona proved to itself and fellow Colorado River basin states, that it still has what it takes to hammer out a hard-fought compromise that ultimately protects the State’s collective interests.

DCP is a plan negotiated by the seven Colorado River basin states to take less water from Lake Mead over the next seven years to prevent the lake from falling to catastrophic levels.  Before agreeing to sign the interstate DCP, the State had to also agree to a plan for how DCP would be implemented in Arizona.  After months of difficult negotiations, a carefully crafted implementation plan, that addresses the major requirements of Arizona’s various water using stakeholders, was put together.

The goal is to protect the Colorado River system by having Arizona, California, Nevada, and Mexico agree to voluntarily use less water to ensure Lake Mead levels do not plummet to dangerously low levels.  Under DCP, Arizona will continue to take the largest share of cuts to its Colorado River water supplies because of the junior priority of the Central Arizona Project that moves a portion of the State's Colorado River water to central Arizona.  California, for the first time ever, has agreed to take reductions when Lake Mead reaches lower levels, something it is not required to do given its water use seniority.   

DCP will not prevent shortages, but it will significantly reduce the risk of far deeper shortages and greater uncertainty on the Colorado River system.  For these reasons, the AMWUA cities support DCP and will contribute significantly to the implementation plan to reduce uncertainty with the delivery of our renewable Colorado River supplies.  

Colorado River Structural Deficit

Colorado River Shortage Preparedness Workshop

Top water resource managers from ADWR, Bureau of Reclamation, and CAP provide the latest information on drought status, shortage probabilities, and anticipated shortage impacts at public meetings. Credit: CAP

What You Can Do

All Arizonans must play a role in improving how we use water.  The AMWUA cities will continue to plan and prepare for a drier future.  For four decades, we have met and exceeded the State’s conservation requirements. We will continue to seek opportunities to use water more efficiently because we know every drop counts.



Colorado River Shortage Preparedness (ADWR)