From Drought to Flood

A Robust Snowpack

“After a brutal series of dry years, water managers are finally breathing a big sigh of relief after the wettest winter season in most of the Colorado River basin since possibly 2011,” said Director of Science and Interstate Matters Dave “DK” Kanzer in his recent Board memo. “It can be summed up in the headline, ‘From Drought to Flood.’”

Across the Western Slope of Colorado, nearly every river basin collected snowpack measuring well above average. In the Yampa/White/Green basin, snowpack broke the historic record in March and significant flooding occurred in the town of Hayden. Down in the Gunnison, snowpack measurements indicated a snow-water equivalent of almost 200% of average, and towns throughout Delta and Montrose Counties are on flood watches after warm days.

Colorado River Basin Forecast Center (CBRFC) Modeled Dust and Water Supply Map

Significant dust events have also influenced the sharp increase in runoff. By decreasing the reflectivity of the snow (or ‘albedo’) the surface temperature of the snowpack increases, leading to faster melting. In some cases, when coupled with warm, dry winds, snow can even sublimate, turning directly from a solid into a gas and not becoming liquid water at all.

On the U.S. West Coast, 31 atmospheric river events slammed into the Sierras this winter. These narrow bands of dense moisture were largely responsible for the dramatic increase in snowfall even here in the Rockies.

Runoff Predictions & implications for Compact Compliance

Meteorologists indicate that we have now shifted into an El Niño cycle, breaking the ‘triple dip’ La Niña. While the central sections of Colorado are often on the border of areas most impacted by increased moisture from a warming Pacific Ocean, the change in these major meteorological patterns is welcome.

“Ocean conditions can have a strong impact, but not always the way we think,” said Kanzer. “We know that La Niña didn’t exactly play out as the models predicted.”

Kanzer explained we’re looking at continued above average precipitation and below average temperatures throughout late spring and early summer. This late peak can be extremely beneficial to environmental health and water quality, allowing rivers to run cold later in the summer.

Looking downstream, runoff into Lake Powell is expected to reflect this generous allotment of moisture. The Bureau of Reclamation’s recently published 24-month study estimates an inflow of approximately 11.3 million acre-feet, a vast improvement on last year’s 6.6 million acre-feet.

Anticipating this healthy runoff, the Bureau is also planning to release up to 9.5 million acre-feet downstream to Lake Mead in 2023, operating within the Lower Balancing Tier as prescribed by the 2007 Interim Guidelines.

While the increased outflow from Powell does aid in propping up the Upper Basin’s Colorado River Compact accounting balance, it will do little to protect Lake Powell’s infrastructure and power production if we return to the megadrought pattern of an extremely dry year following a wet one – as seen after the 2011 and 2019 high water winter seasons.

Local Reservoirs

Almost all the reservoirs on the Western Slope of Colorado are expected to fill in Water Year 2023. Don Meyer, Senior Water Resources Engineer, provided the following list of reservoirs along with their predicted inflow, and an estimate of how water might be ‘spilled’ this year.

A spillway is a component of a dam allowing for a controlled, rapid release of water. In wet years with high runoff conditions, spillways help prevent breaching or over-topping of dams during flood conditions by offering a second option for releasing water from the reservoir.

April 17, 2023: Runoff Forecast