A guest post from Jack Schmidt, crossposted from Utah State University’s Center for Colorado River Studies

By Jack Schmidt | March 8, 2024

Reservoir storage didn’t change much in February 2024, demonstrating that the Basin’s water managers and users have succeeded in retaining the bounty of last year’s big runoff.

This month’s assessment of Colorado River reservoir storage will be short and to-the-point.  A month from now (April 1) the traditional snow accumulation season will end, and I’ll provide a more comprehensive assessment of the status of the basin’s water supply.

What happened in February?

Total basin water storage was 28 million af (acre feet) on 29 February 2024 (Fig. 1). Since mid-December 2023, basin storage progressively increased bit by bit — by 32,000 af in February. The small value of the increase matters little; what matters is that basin storage did not decrease and hasn’t for the last 2.5 months. To date, reservoir storage is only 20% less than the peak storage at the end of the 2023 runoff season. This is a very small loss in relation to the rate at which the bounty of previous runoff years had been consumed. Nevertheless, conditions in the basin are comparable to conditions in early May 2021, a perilous situation.

Figure 1. Graph showing total basin reservoir storage and total storage in Lake Mead and Lake Powell since January 2021. This graph demonstrates the efficient retention of reservoir storage accomplished this year, the result of reductions in consumptive use and addition of winter precipitation. The black arrows indicate the last time reservoir storage matched current conditions.

Although basin storage has not changed, the distribution of storage within the basin has somewhat changed, with storage being systematically shifted downstream. The combined storage in federal units of the Colorado River Storage Project upstream from Lake Powell (Flaming Gorge, Navajo, Fontenelle, Blue Mesa, Morrow Point, and Crystal) peaked in mid-July 2023 at 5.8 million af, and steadily declined thereafter (Fig. 2). In February, the combined storage in these reservoirs declined an additional 79,000 af to 5.0 million af.

Figure 2. Graph showing total basin reservoir storage (solid blue line) and storage in the different parts of the watershed. Notably, storage in Lake Mead has steadily increased during the past 18 months, while storage in Lake Powell has fluctuated more. Storage in CRSP reservoirs upstream from Lake Powell has steadily decreased since summer 2023, but is larger today than during the previous 2 years.

Similarly, storage in Lake Powell peaked in mid-July 2023 at 9.7 million af, but was 7.9 million af at the end of February 2024. Storage in Lake Powell declined by 203,000 af in February. Conversely, storage in Lake Mead reached its nadir in August 2022 at 7.0 million af and has steadily increased thereafter to 9.7 million af at the end of February. Storage in Lake Mead increased by 310,000 af in February with most of that water coming from Lake Powell releases. Today, Lake Mead has 1.8 million af more water than does Lake Powell. The combined storage in the two reservoirs was 17.7 million af on 29 February, 109,000 af more than at the end of January.

Let’s hope for another good month of precipitation in March.