Colorado River Basin hydrology forecasts paint grim picture

Dave Kanzer, deputy chief engineer, and Don Meyer, senior water resources engineer, provided a disheartening update to the Colorado River District Board of Directors on the continuing drought and dire water supply outlook in 2021Unfortunately, conditions have only worsened since January.  

For most of the last two years, monthly precipitation amounts have been below average within the Colorado River District. As of April 30the snow water equivalent is well below average across the Western Slope with the Colorado basin at 72% of averagethe Gunnison at 62% and the Yampa & White at 72%. 

In addition to the below-average seasonal snowpack, the temperature and precipitation model forecasts from the National Weather Service’s Climate Prediction Center are predicting a hot and dry summer with above-average temperatures across most of the southwest. Forecasters also predict below-average precipitation, particularly in the Upper Colorado River Basin. Most of the Colorado River Basin is currently in extreme or exceptional drought conditions. 

Adding insult to injury, low soil moisture will adversely impact runoff.  Models from the Colorado Basin River Forecast Center suggest the majority of the Upper Colorado River Basin has such low soil moisture that it will require up to 12 inches of water to reach saturation. This means that most of the snowpack is absorbing into the soils and not turning into runoff. With the sizable reservoir drawdowns from last year, very few reservoirs are likely to fill in the upcoming water year. This soil moisture deficit presents a significant challenge to refilling the Colorado River storage system, especially the lower, larger facilities, like Lakes Powell and Mead.  

The U.S. Bureau of Reclamation’s mid-term modeling forecasts project this water year to be below average, with inflow into Lake Powell at about 5.13 million acre-feet, less than 47% of the long-term average. Furthermore, Reclamation projects that Lake Powell will end the water year near 3,557.03 feet elevation, holding about 8.10 million acre-feet in storage, which is 33% of its capacity.  

With these projections for Lake Powell, combined with similarly low projections for Lake Mead, Drought Contingency Plan operations will continue to be in effect for the Lower Basin in 2021 with lowered deliveries to the Central Arizona Project, Southern Nevada and Mexico. Should these projections continue to play out, the Lower Basin will enter a higher tier of shortage in 2022, prompting mandatory cutbacks under the 2007 Interim Guidelines.  

If the level of Lake Powell is projected to fall below 3,535 feet in elevation by October 2022   which is currently within the worst-case scenario forecast  it would activate the Upper Basin Drought Contingency Plan. This would trigger coordinated releases into Lake Powell from Flaming Gorge Reservoir and other upstream reservoirs to protect reservoir levels and maintain power generation at Glen Canyon Dam.  

There is still time for conditions to improve, but the outlook is not good.  

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