Colorado River shortage: How does it affect California?

On Aug. 16, the U.S. Bureau of Reclamation declared a water shortage on the Colorado River for 2022. While this announcement was expected, this marked the first declaration of shortage on the Colorado River. As a consequence of shortage, there will be a significant reduction in the quantity of Colorado River water that will be delivered in the Lower Basin in 2022.

In its study announcing the shortage, Reclamation estimates that the water elevation at Lake Mead on Jan. 1, 2022 will be below 1,075 feet. This projected elevation triggers a Tier 1 shortage under which certain users will not receive Colorado River water in 2022.

The good news for California is that, in contrast to the other Lower Basin states (Arizona and Nevada), California's users face no reduction in their annual Colorado River supply in 2022 under a Tier 1 shortage. In fact, California does not face a reduction until the water elevation in Lake Mead is projected to fall below 1,045 feet.

The bad news for California is that Reclamation's study suggests that a shortage impacting California's Colorado River deliveries is a strong possibility in 2024. Reclamation currently projects that Lake Mead's elevation will fall below 1,038 feet during the summer of 2023. If that projection proves to be reasonably accurate, it would seem likely that Reclamation will declare a Tier 2b shortage (below 1,045) or a Tier 2c shortage (below 1,040) for 2024. California could be curtailed in 2023, but, under current projections, that possibility is more remote.

Under a Tier 2b shortage, California would relinquish 200,000 acre-feet annually of its Colorado River allocation. Tier 2c would result in a loss of 250,000 acre-feet.

If Lake Mead continues to drop, California's annual relinquishment would increase to as much as 300,000 acre-feet (Tier 2d, below 1,035 feet) or 350,000 acre-feet (Tier 2e, below 1,030 feet, or Tier 3, below 1,025 feet) annually.

One acre-foot is the amount of water that would cover an acre of land (roughly the size of a football field) one-foot deep. This is enough water to support two typical households for a year. Accordingly, the hundreds of thousands of acre-feet that California's Colorado River users could be forced to relinquish in 2024 and beyond is, by any standard, a significant amount of water.

Arizona's situation provides some perspective on the magnitude of California's potential cuts. The impacts to Arizona are far more drastic. With Lake Mead's elevation triggering a Tier 1 shortage next year, Arizona will immediately relinquish 512,000 acre-feet of Colorado River water in 2022, while California relinquishes nothing. 512,000 acre-feet represents approximately 18% of Arizona's annual Colorado River apportionment, and the effects of Tier 1 shortage in Arizona will be borne primarily by agricultural water users. By the time California faces a Tier 2b relinquishment of 200,000 acre-feet, Arizona's annual relinquishment will have increased to 640,000 acre-feet. If elevation drops below 1,025 (Tier 3), California's relinquishment would be 350,000 acre-feet, but Arizona's relinquishment (720,000 acre-feet) would be more than double that quantity.

When and if they occur, California's relinquishments will be borne primarily by the Metropolitan Water District of Southern California. Metropolitan is a state-established cooperative comprised of 26 member cities and water agencies. Metropolitan enjoys a diverse -- and very large -- water portfolio. As such, Metropolitan would typically be (relatively) well-positioned to manage relinquishments of the magnitudes described above.

This is not to suggest that California doesn't face significant water issues; California most certainly does. However, when viewed in isolation, the Colorado River shortage is less concerning than California's other water challenges. The true threat to California's water security is that these water supply problems are all mounting in unison.

The challenge for Metropolitan will be that any relinquishments of Colorado River that occur are likely to be compounded by simultaneous reductions in other water sources. The same long-term regional drought conditions that have caused water in the Colorado River and its system of reservoirs to diminish have likewise resulted in a significant decline in California's internal water resources. This, in turn, prompted California to enact the Sustainable Groundwater Management Act, which serves to dramatically restrict groundwater withdrawals -- at a time when reliance on groundwater would typically be increasing in response to the dwindling availability of surface water.

One significant component of Metropolitan's portfolio is water imported from Northern California through the State Water Project. In March, the California Department of Water Resources announced that State Water Project deliveries would be limited to 5% of requested volumes. According to Metropolitan, this results in its loss of the equivalent of 11 out of 12 months of its Northern California water supply.

With all of these drought-induced impacts coalescing at once, Metropolitan issued a "Water Supply Alert" on Aug. 17, the day following Reclamation issued its Tier 1 declaration for 2022. Under Metropolitan's framework for classifying the urgency of conserving Southern California's water supply, a Water Supply Alert is the second-most serious condition. It calls for local agencies to implement drought ordinances and other conservation measures. If conditions worsen, the next step would be the implementation of a "Water Supply Allocation Plan" that would direct how water supplies are allocated to Metropolitan's member cities and agencies if available water supplies are insufficient to meet demands.

If trends continue and Lake Mead's water levels continue to drop, California will lose significant quantities of its Colorado River supply in the coming years. It is probably the case that, in isolation, California is equipped to manage the loss of these magnitudes? The more important questions are "How bad will the drought get?" and "For how long?" The ultimate story about how dire the water supply becomes will be told not just about drought on the Colorado River, but by the regional drought causing a significant diminishment of each component of California's annual water budget. 