5-Year Probabilistic Projections

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In February 2022, Reclamation switched from using the Colorado River Simulation System (CRSS) to using the Colorado River Mid-term Modeling System (CRMMS) to provide the 5-Year Probabilistic Projections. This presentation provides an explanation of the changes to the 5-year projections due to switching models.

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 in February of 2022 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.

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.

Chance of Reaching Critically Low Reservoir Elevations
CRMMS-ESP/CRSS January 2022 vs. CRMMS-ESP February 2022
Run WY 2022 WY 2023 WY 2024 WY 2025 WY 2026
Lake Powell less
than 3,525 feet
January 2022 87% 42% 39% 36% 37%
February 2022 90% 77% 50% 50% 37%
Difference 3% 35% 11% 14% 0%
Lake Powell less
than 3,490 feet
(minimum power pool)
January 2022 N 8% 20% 23% 26%
February 2022 N 23% 27% 27% 23%
Difference - 15% 7% 4% -3%
Lake Powell less
than 3,375 feet
(dead pool = 3,370 feet)
January 2022 0% 0% 0% 0% 0%
February 2022 0% 0% 0% 0% 0%
Difference 0% 0% 0% 0% 0%
Run 2022 2023 2024 2025 2026
Lake Mead less
than 1,020 feet
January 2022 0% <1% 36% 40% 47%
February 2022 0% 0% 20% 33% 37%
Difference 0% 0% -16% -7% -10%
Lake Mead less
than 1,000 feet
January 2022 0% 0% 3% 17% 20%
February 2022 0% 0% 7% 13% 17%
Difference 0% 0% 4% -4% -3%
Lake Mead less
than 950 feet
(minimum power pool)
January 2022 0% 0% 0% <1% 3%
February 2022 0% 0% 0% 0% 0%
Difference 0% 0% 0% 0% -3%
Lake Mead less
than 900 feet
(dead pool = 895 feet)
January 2022 0% 0% 0% 0% <1%
February 2022 0% 0% 0% 0% 0%
Difference 0% 0% 0% 0% 0%
*All results computed as the chance of falling below the threshold in any month in the calendar (water) year for Lake Mead (Lake Powell).
Chance of Reservoir Operating Conditions
February 2022 CRMMS-ESP Projections
Upper Basin - Lake Powell - Operating Condition 2022 2023 2024 2025 2026
Equalization Tier (Powell >= Equalization [EQ] Elevation) 0 0 3 7 13
Equalization - annual release > 8.23 maf 0 0 3 7 13
Equalization - annual release = 8.23 maf 0 0 0 0 0
Upper Elevation Balancing Tier (Powell < EQ Elevation and >= 3,575 ft) 0 7 13 20 13
Upper Elevation Balancing - annual release > 8.23 maf 0 7 13 20 13
Upper Elevation Balancing - annual release = 8.23 maf 0 0 0 0 0
Upper Elevation Balancing - annual release < 8.23 maf 0 0 0 0 0
Mid-Elevation Release Tier (Powell < 3,575 and >= 3,525 ft) 100 43 50 33 43
Mid-Elevation Release - annual release = 8.23 maf 0 0 0 0 17
Mid-Elevation Release - annual release = 7.48 maf 100 43 50 33 27
Lower Elevation Balancing Tier (Powell < 3,525 ft) 0 50 33 40 30
Lower Elevation Balancing - annual release > 8.23 maf 0 20 17 17 10
Lower Elevation Balancing - annual release < 8.23 maf 0 30 17 23 20
Lower Basin - Lake Mead - Operating Condition 2022 2023 2024 2025 2026
Surplus Condition - any amount (Mead >= 1,145 ft) 0 0 0 0 0
Surplus - Flood Control 0 0 0 0 0
Normal Year or ICS Surplus Condition (Mead < 1,145 and > 1,075 ft) 0 0 7 7 7
Recovery of DCP ICS / Mexico’s Water Savings (Mead >/>= 1,110 ft) 0 0 0 0 0
DCP Contribution / Mexico’s Water Savings (Mead <= 1,090 and > 1,075 ft) 0 0 7 3 0
Shortage Condition - any amount (Mead <= 1,075 ft) 100 100 93 93 93
Shortage / Reduction - 1st Level (Mead <= 1,075 and >= 1,050 ft) 100 87 23 17 27
DCP Contribution / Mexico’s Water Savings (Mead <= 1,075 and >= 1,050 ft) 100 87 23 17 27
Shortage / Reduction - 2nd Level (Mead < 1,050 and >= 1,025 ft) 0 13 67 47 27
DCP Contribution / Mexico’s Water Savings (Mead < 1,050 and > 1,045 ft) 0 13 10 13 7
DCP Contribution / Mexico’s Water Savings (Mead <= 1,045 and > 1,040 ft) 0 0 10 3 3
DCP Contribution / Mexico’s Water Savings (Mead <= 1,040 and > 1,035 ft) 0 0 27 10 7
DCP Contribution / Mexico’s Water Savings (Mead <= 1,035 and > 1,030 ft) 0 0 10 10 3
DCP Contribution / Mexico’s Water Savings (Mead <= 1,030 and >=/> 1,025 ft) 0 0 10 10 7
Shortage / Reduction - 3rd Level (Mead < 1,025 ft) 0 0 3 30 40
DCP Contribution / Mexico’s Water Savings (Mead </<= 1,025 ft) 0 0 3 30 40
*All results computed as the percent of traces with a system condition. Percentages shown in this table may not be representative of the full range of future possibilities that could occur with different modeling assumptions.

Download Tables

Archived Tables

Previous tables (starting in January 2012) are also available. Select the date (a new window will open):

The following two figures show a combination of historical and projected reservoir elevations for Lake Powell and Lake Mead.

Projections of Lake Powell (top) and Lake Mead (bottom) end-of-month reservoir elevations. The colored region, or cloud, for the scenario represents the minimum and maximum of the projected reservoir elevations. The gray colored region represents the range of uncertainty from a recent CRSS projection, illustrating that there are possible scenarios outside of the CRMMS-ESP projected range. Solid lines represent historical elevations (black), and median projected elevations for the scenario (yellow). Dashed and dot dashed lines represent the 10th and 90th percentiles, respectively. Horizontal gray lines represent important elevations for operations.


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Last updated: 2022-02-25