Reclamation Lower #ColoradoRiver region 5-Year Probabilistic Projections #COriver #aridification

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In light of the prolonged drought, low runoff conditions, and depleted storage at Lake Powell, the Department of the Interior implemented an action under Sections 6 and 7.D of the 2007 Interim Guidelines specifically reducing the Glen Canyon Dam annual releases to 7.00 maf in water year 2022. This action was undertaken in conjunction with 2022 Drought Response Operations Plan actions, which includes an additional 500 kaf release from Flaming Gorge. Together these actions are anticipated to add approximately one million additional acre-feet of storage to Lake Powell by 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 0.48 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.

Overview

Five-Year Probabilistic Projections of future conditions in the Colorado River system currently extend through 2026. They are typically updated every January, April, and August, while probabilistic results for the 2-year period are updated every month. The 5-Year Probabilistic Projections are generated using the Colorado River Mid-term Modeling System (CRMMS) in Ensemble Mode. CRMMS Ensemble Mode is driven by an ensemble of monthly unregulated streamflow forecasts developed by the National Weather Service Colorado Basin River Forecasting Center (CBRFC) using the Ensemble Streamflow Prediction (ESP) method. Results from CRMMS run with ESP are referred to as CRMMS-ESP.

The most recent 5-year projections of future Colorado River system conditions were produced using the following assumptions:

  • Initial Conditions: CRMMS is initialized with previous end-of-month reservoir elevations.
  • Hydrology: Upper Basin inflows are 30 unregulated inflow forecasts traces produced by the CBRFC using the ESP method, which relies on observed temperature and precipitation from 1991-2020. Lower Basin inflows are the historical intervening flows from 1991-2020 that align with the ESP traces.
  • 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: 2007 Interim Guidelines, Lower Basin Drought Contingency Plan, and Minute 323 are modeled reflecting Colorado River policies.
  • Drought Response Actions: CRMMS projections contain actions undertaken with the 2022 Drought Response Operations Plan and 2022 Glen Canyon Dam operational adjustment.
    • The 2022 Drought Response Operations Plan includes an additional release of 500 kaf from Flaming Gorge from May 2022 through April 2023.
    • The 2022 Glen Canyon Dam operational adjustment reduces the releases from Lake Powell from 7.48 maf to 7.00 maf in water year 2022. This will result in a reduced release volume of 0.48 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. Recognizing that operational decisions for 2023 and beyond have not been made, for all hydrologic scenarios that project Glen Canyon Dam to operate in a balancing condition in a future water year, releases are simulated in a manner that attempts to preserve the benefits to Glen Canyon Dam facilities and operations.

 Additional details are available in CRMMS Ensemble 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

5-Year Probabilistic Projections presented in the tables below are reported as the percentage of projected Lake Powell and Lake Mead operations that fall below critically low elevations or are within each operational tier in the next five years.

Click the graphic to enlarge.
Click the graphic to enlarge.

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