What the Coming Colorado River Shortage Means for Arizona

Sarah Porter, Director
Kyl Center for Water Policy
ASU Morrison Institute for Public Policy


In 2022, for the first time ever, Arizona’s Colorado River supplies will be cut. Lake Mead, the large reservoir that holds Colorado River water for Arizona, California, New Mexico and Mexico, has been shrinking for over two decades, and next year’s cuts are part of a multi-state plan aimed at preventing the reservoir from falling to critically low levels. 

Arizona’s Colorado River allocation is divided between on-river users along the state’s western border and users who get their water via the Central Arizona Project (CAP), the 330-mile canal that conveys water from Lake Havasu to Maricopa, Pinal and Pima Counties. About 60% of Arizona’s Colorado River supplies are allocated to CAP users. 

Pinal County farmers will absorb almost all of next year’s cut, which amounts to about 30% of the water the CAP delivers. In years to come, the cuts could be larger and impact higher priority users, including Central Arizona cities. 

Why is Lake Mead declining? 

Several factors have contributed to Lake Mead’s ongoing decline. To start with, the Colorado River is over-allocated, and in recent years more and more users have been taking their full allocations. Two decades of drought have compounded the problem, and many experts point to evidence that as a result of climate change the Colorado Basin is aridifying, resulting in permanently reduced flows. 

Over the years, the Colorado Basin states have implemented measures to address the problem of declining water supplies. In 2019, they agreed to the Drought Contingency Plan (DCP), which includes provisions that enable water users to conserve water in Lake Mead as well as provisions for users to take increasingly large cuts as lake levels fall. 

While the DCP bought the region a little time, it has not solved the problem. Projections in August indicated that without further action, Lake Mead could hit a dangerously low elevation within the next two years. In response, Arizona, California and Nevada have announced a plan to pay more water users to leave their allocations in the reservoir, almost doubling the conservation contemplated by the DCP. The State of Arizona will contribute $40 million to make that happen. 

These measures will buy more time, but in the long run Colorado River water users will likely have to find their way to use less of it in order to keep the system functional. 

Are cities prepared? 

Central Arizona cities have had years to prepare for reduced Colorado River supplies. They have banked water in aquifers. They have figured out innovative ways to maximize use of treated waste-water (also known as “reclaimed water”). Some cities have limited the influx of new high-volume water users. And cities are looking to demand management – permanent reductions in per capita water use – as an important tool for future water resilience. 

There is no one-size-fits-all solution for cities, because each municipality’s supply portfolio is unique. For example, some of the older cities in the Phoenix area have rights to substantial amounts of water from the SRP system as well as Colorado River water. Some cities rely more heavily on groundwater. Some cities have already secured the water they need for their projected growth while others are still working to secure long-term water supplies. 

There are concepts for developing new water supplies for Arizona communities, many of which are explored in the Kyl Center’s Augmentation Concepts story map. But it is unclear whether and how much additional water will be needed, in part because economic and population growth have been largely “decoupled” from water demand. In the last twenty years, the population of Maricopa, Pinal and Pima Counties has grown by 45% but municipal water demand has increased by only 14%. 

One thing is clear: Arizona faces important challenges and choices as it transitions to lower reliance on Colorado River supplies. You can read more about these here

Sarah Porter, Director
Kyl Center for Water Policy
ASU Morrison Institute for Public Policy