The U.S. Bureau of Reclamation’s April 24-Month Study, published this week, as expected, signals a significant likelihood of reduced water deliveries in the Lower Basin of the Colorado River to Arizona, California, and Nevada. Not only does it suggest a high likelihood of Tier 1 reductions for 2022 and 2023, but it also suggests that the Lower Basin is at higher risk of confronting Tier 2 conditions.
As I have discussed previously, The operational tiers are a product of the Bureau of Reclamation’s December 2007 Record of Decision on Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations of Lake Powell and Lake Mead (“Interim Guidelines”), which prescribes cuts of water deliveries to some of the states in the Colorado River Basin when the water at Glen Canyon Dam (Lake Powell) and Hoover Dam (Lake Mead) reach certain levels, or tiers. When the Lower Basin States (Arizona, California, Nevada) voluntarily adopted the Lower Basin Drought Contingency Plan (“DCP”), an additional tier, Tier Zero, was added to the Interim Guideline tiers to provide even greater protection in shortage conditions. The DCP also made deeper cuts to water deliveries if the other tiers are reached, and even California agreed to take cuts to their deliveries in some tiers (California was not required to take cuts under the Interim Guidelines).
When certain elevations are reached at Hoover Dam on Lake Mead, cuts to water deliveries are made in accordance with the predetermined guidance of the Interim Guidelines and the DCP (See Figure 1, below).
The recent April 24-Month Study predicts that the water elevation on Hoover Dam will dip below 1,075 feet by June 2021 and continue to decrease well into 2022. The study shows that the elevation may even dip below 1,050 feet (the level to trigger Tier 2) in November 2022 before bouncing back up above 1,050 feet in December of that year.
While this could all change with significant spring snowfall and a strong monsoon season, this is what the Lower Basin has been preparing for. We will know for sure in five months when BOR’s August 24-Month Study is published. If the August study makes a Tier 1 shortage official, it will be the moment of truth where we start to test the plans that have been developed in the Lower Basin states to handle shortages of Colorado River water. The Arizona Department of Water Resources and the Central Arizona Project will have a joint public briefing on April 29, 2021 to discuss those plans.