The hydrology in 2020 began with optimism and promise, but ended with a disappointing runoff and inflow to Lake Powell. We will continue to operate in Tier Zero in 2021, as we did in 2020. Tier Zero operations include a reduction of 192,000 acre-feet to CAWCD, impacting supplies available for water banking, aquifer replenishment and a modest reduction to CAP’s agriculture supplies. Although Tier Zero is good news for 2021, it’s important to note that the disappointing inflows in 2020 have pushed the outlook for 2022 (which will be announced by the U.S. Bureau of Reclamation in August 2021) toward the possibility of larger reductions under potential Tier 1 conditions.
Here’s a brief recap of the 2020 conditions in the Colorado River Basin:
- 2020 was the first year operating under the Drought Contingency Plan(DCP) Tier Zero, which begins at Lake Mead elevation 1090’and extends to 1075’.
- Thanks to DCP reductions and continued conservation and storage contributions, Lake Mead continued to remain stable, ending 2020 at 1084’.
- The end of the snow accumulation season showed a near-normal snowpack across the Upper Colorado River Basin.
- The April 2020 runoff projections showed inflows to Lake Powell on the order of about 80% of the long-term median. These projections reflected the influence of dry fall 2019 conditions, which were projected to reduce the conversion of snowpack to runoff in spring-summer 2020.
- The hot, dry spring and summer 2020 further depleted the runoff into Lake Powell. By the end of the runoff season, the inflows to Lake Powell were about 55% of the long-term median.
- The hot and dry conditions persisted into the fall 2020.
The reduced inflows to Lake Powell in 2020, absent normal inflows in the spring and summer of 2021, will trigger reduced releases from Lake Powell in water year 2021 and 2022, causing a drop in Lake Mead elevations. This could result in Tier 1 (1075 – 1050’) for 2022 operations.
Under Tier 1, Arizona would be required to reduce uses by 512,000 acre-feet, to Arizona’s 2.8 MAF entitlement, borne almost entirely by CAWCD. This reduction, almost 30% of the CAP supply, is significant and will impact CAP’s many water users. However, there would be no immediate impact to municipal and tribal water supplies under a Tier 1 shortage. Due to the Arizona Implementation Plan that was developed in 2019 for DCP, plans and agreements are in place to manage these reductions within the state. The Tier 1 reductions would be partially mitigated through the implementation of several innovative shortage-sharing and mitigation agreements, which would eliminate water banking and replenishment and severely curtail the agriculture supply. The cooperation and collaboration developed in the Arizona DCP process continues to benefit Arizona water users, even in the face of potentially deeper reductions in 2022.
The potential Tier 1 conditions in 2022 are far from certain. As we have seen and experienced over previous years, you never know what a year can bring!