24-Month Study Projections


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. The Most Probable and Probable Minimum 24-Month Studies are released monthly, typically by the 15th day of the month. The Probable Maximum 24-Month Study is released alongside other 24-Month Studies in January, April, August, and October.

  • 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: The 2022 Drought Response Operations Agreement (DROA) Plan for May 2022 through April 2023 was amended to suspend 2022 DROA Plan releases as of March 7, 2023. A total DROA release of approximately 463 kaf occurred under the 2022 DROA Plan. Reclamation will attempt to maximize DROA recovery in the Upper Initial Units in water year 2023 and through April 2024. CRMMS modeling does not include any assumptions regarding future DROA releases.

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.


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: 2023-08-30