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 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 45 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.” Twenty 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. 

The Drought Contingency Plan

DCP Graphic 1To better protect Colorado River supplies, the seven Basin States and Mexico have agreed to take even less water than previously decided. This new agreement is called the Drought Contingency Plan (DCP), and lasts through 2026. DCP requires the Basin States to take progressively less water as the amount stored in reservoirs declines. By using less water sooner, we reduce the risk of more painful cutbacks later. As the lowest priority water user on the Colorado River, Arizona must reduce the amount of water it takes before the other states.

How Does This Affect Arizona?

Lake Mead Elevation GraphicArizona has its own, internal priority system for distributing Colorado River water within the State. The lowest priority water is used primarily by agriculture and developers. Some tribes and cities also have lower priority supplies that will be reduced. Because the DCP cutbacks would have severe impacts on agricultural water users, a plan was formulated to help them cope with less Colorado River water.

The Arizona Implementation Plan
The Implementation Plan is an arrangement within Arizona to help water users who face supply reductions under DCP. To mitigate the impact of these reductions, water users are provided alternative water supplies or funding. The alternative water supplies come from water previously stored underground and in Lake Mead. Because of Arizona’s internal priority system, cutbacks to tribes and cities must be mitigated first, before agricultural users can receive resources.

In addition to mitigation, other water users are being paid to conserve water that they would normally use. This helps boost the water levels in Lake Mead.

AMWUA Cities' Commitment to Implementation Plan
AMWUA cities have committed substantial resources to support the Implementation Plan. This includes sending nearly 100,000 acre-feet of water to Pinal farms to help mitigation DCP impacts. Water rates for AMWUA cities will increase under DCP. Those same rates will fund $60 million worth of mitigation supports. Under DCP, cities are taking reductions in their water supplies that have already been paid for.

How Is the Implementation Plan Funded?
BOD   Updated DCP Fact Sheet Page 2Funding is needed to purchase mitigation resources, and to pay water users to voluntarily use less. The funds come from a variety of sources, including state tax dollars, water rates, private donors, and potentially the federal government. The Implementation Plan is expected to cost at least $130 million.

What Happens Next?
On May 20th 2019, the Basin States signed the DCP agreements into effect. Thanks to a wetter than normal winter, Arizona will not have to bear the larger reductions of a Tier 1 shortage under DCP in 2020. However, because DCP includes earlier cutbacks, in August, a Tier 0 shortage will likely be declared for 2020 resulting in the first mandatory cutbacks. Fortunately, since 2015, Arizona has been voluntarily reducing its use by similar amounts, which leaves water uses well-prepared for a Tier 0 shortage.

Even with the wet winter, major reservoirs are still less than half-full. The signing of DCP is very important to reducing the likelihood of more drastic cutbacks should the next winters be drier. DCP also provides time for the Basin States and Mexico to determine what happens after 2026 when existing shortage agreements expire. When the first stage of shortage is inevitably declared for the Colorado River, Arizona’s internal Implementation Plan will provide enough mitigation to ensure that cities and tribes are not impacted. Agricultural users will also receive water and funding in order to continue reduced operations as they transition to utilizing more groundwater.

Colorado River Structural Deficit

Atop Hoover Dam, Arizona participates in historic agreement to protect the Colorado River system and Lake Mead.

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)