24-Month Study Projections

Overview

The 24-Month Study projects future Colorado River system conditions using single-trace hydrologic scenarios simulated with the Colorado River Mid-term Modeling System (CRMMS) in 24-Month Study Mode. Three Studies, the Most, Minimum, and Maximum Probable 24-Month Studies, are released monthly, typically by the 15th day of the month.

  • Initial Conditions: The 24-Month Study is initialized with previous end-of-month reservoir elevations.
  • Hydrology: In the Upper Basin, the first year of the Most Probable inflow trace is based on the 50th percentile of Colorado Basin River Forecast Center (CBRFC) forecasts and the second year is based on the 50th percentile of historical flows. To represent dry and wet future conditions, the Minimum Probable and Maximum Probable traces use the 10th and 90th forecast percentiles in the first year and the 25th and 75th percentiles of historical flows in the second year, respectively. The Lower Basin inflows are based only on historical intervening flows that align with the Upper Basin percentiles.
  • Water Demand: Upper Basin demands are estimated and incorporated in the unregulated inflow forecasts provided by the CBRFC; Lower Basin demands are developed in coordination with the Lower Basin States and Mexico.
  • Policy: Reservoir operations are input manually in the 24-Month Study by reservoir operators and align with Colorado River policies.
  • Drought Response Actions: CRMMS projections contain actions undertaken with the 2022 Drought Response Operations Plan, 2022 Glen Canyon Dam operational adjustment, and the 2023 operations described in the 24-Month Study.
    • The 2022 Drought Response Operations Plan includes an additional release of 500 kaf from Flaming Gorge from May 2022 through April 2023.
    • The reduction of releases from Lake Powell from 7.48 maf to 7.00 maf in water year 2022 will result in a reduced release volume of 0.480 maf that normally would have been released from Glen Canyon Dam to Lake Mead as part of the 7.48 maf annual release volume, consistent with routine operations under the 2007 Interim Guidelines. The reduction of releases from Glen Canyon Dam in water year 2022 (resulting in increased storage in Lake Powell) will not affect future operating determinations and will be accounted for “as if” this volume of water had been delivered to Lake Mead. The August 2022 24-Month Study modeled 2023 and 2024 operations at Lakes Powell and Mead as if the 0.480 maf had been delivered to Lake Mead for operating tier/condition determination purposes for the Lower Basin States and for Mexico.
    • Because the 2022 operations were designed to protect critical elevations at Lake Powell, Reclamation will implement Lower Elevation Balancing Tier operations in a way that continues to protect these critical elevations, or preserves the benefits of the 2022 operations to protect Lake Powell, in water year 2023. Specifically, Reclamation modeled operations in WY 2023 as follows in the 24-Month Studies:
      • The Glen Canyon Dam annual release has initially been set to 7.00 maf, and in April 2023 Reclamation will evaluate hydrologic conditions to determine if balancing releases may be appropriate under the conditions established in the 2007 Interim Guidelines;
      • Balancing releases will be limited (with a minimum of 7.00 maf) to protect Lake Powell from declining below elevation 3,525 feet at the end of December 2023;
      • Balancing releases will take into account operational neutrality of the 0.480 maf that was retained in Lake Powell under the May 2022 action. Any Lake Powell balancing release volume will be calculated as if the 0.480 maf had been delivered to Lake Mead in WY 2022; and
      • The modeling approach for WY 2023 will apply to 2024.

Consistent with the provisions of the 2007 Interim Guidelines, and to preserve the benefits to Glen Canyon Dam facilities from 2022 Operations into 2023 and 2024, Reclamation will consult with the Basin States on monthly and annual operations. Reclamation will also ensure all appropriate consultation with Basin Tribes, the Republic of Mexico, other federal agencies, water users and non-governmental organizations with respect to implementation of these monthly and annual operations.

Reclamation will continue to carefully monitor hydrologic and operational conditions and assess the need for additional responsive actions and/or changes to operations. Reclamation will continue to consult with the Basin States, Basin Tribes, the Republic of Mexico and other partners on Colorado River operations to consider and determine whether additional measures should be taken to further enhance the preservation of these benefits, as well as recovery protocols, including those of future protective measures for both Lakes Powell and Mead.

For more detailed information about the approach to the 24-Month Study modeling, see the CRMMS 24-Month Study Mode page. All modeling assumptions and projections are subject to varying degrees of uncertainty. Please refer to this discussion of uncertainty for more information.

Projections

The latest 24-Month Study reports for each study can be found at the links below:

Archived 24-Month Study results are also available. Descriptions of the 24-Month Study hydrologic scenarios are also documented in Monthly Summary Reports. Lake Powell and Lake Mead end-of-month elevation charts are shown below.

Projected Lake Powell end-of-month physical elevations from the latest 24-Month Study inflow scenarios.

Projected Lake Mead end-of-month physical elevations from the latest 24-Month Study inflow scenarios.


For additional information or questions, please contact us via email at: .

Last updated: 2022-08-16