The amount of water predicted to flow into Lake Powell this year is down slightly from the previous month, according to the May report from the National Oceanic and Atmospheric Administration’s Colorado Basin River Forecast Center.
“The last couple months have steadied out a little bit,” Cody Moser, a senior hydrologist with NOAA forecast center, said during a recent web briefing to review the most recent report. “But generally below-normal precipitation the last several months after a very wet December.”
The NOAA forecast center begins releasing monthly water supply forecasts for the Colorado River Basin in December. The May report, released last week, is the final runoff prediction for the season. The forecast estimated that the amount of water that will flow into Lake Powell this spring and summer will be about 59% of average, based on 30 years of data from 1991 to 2020. In January, following the wet December Moser noted, the NOAA forecast called for 98% of the 30-year average to reach Powell.
It wasn’t just the Powell number that dipped, although the amount of runoff that makes its way to Powell each year is considered a good barometer for conditions basinwide. “Water supply forecast volumes decreased across most of the region,” Moser said during the webinar.
A 59% flow into Powell translates to about 3.8 million acre-feet. That spring runoff is critical to irrigated agriculture, domestic water supplies, and the recreation industry in Colorado and the West. About 40 million people rely on the Colorado River for domestic use and farmers and ranchers use water from the river to irrigate more than 3 million acres of farmland.
“By May 1, the spring-summer runoff outcomes are pretty well locked in, which means there’s virtually no escape from a third poor runoff year in a row,” Jeff Lukas, an independent water and climate researcher based in Lafayette, said in an email. “Across most of the streams and rivers of the Upper Basin, forecasted runoff ranges from very poor (50% of average) to mediocre (80% of average).”
Both Moser and Lukas said that dry soil moisture conditions across the Colorado River Basin, which can sponge off valuable runoff before the water makes it into rivers and streams, won’t be quite as bad as last year but will still be a negative factor.
“Soil moisture conditions have improved over the last year across most of Colorado’s Western Slope, but that’s not necessarily saying much because of how bad soil moisture conditions were heading into last year’s snowmelt runoff season,” Moser said.
He said the soil moisture conditions were still well below normal across western Colorado, particularly in the southwest part of the state.
Lukas noted that the dry soil conditions are factored into the NOAA runoff predictions from the get-go so there shouldn’t necessarily be any big surprises with that particular variable.
Federal and state water managers have watched the water level in Lake Powell closely this year. Last week, the Bureau of Reclamation announced “extraordinary action” to keep the water level at Powell from dropping too low, which could threaten hydropower production at Powell’s Glen Canyon Dam.
The bureau, in consultation with tribal nations and the seven Colorado River Basin states, decided to keep nearly 500,000 acre-feet of water in Lake Powell that had originally been planned to be released to the Lower Basin states of Nevada, Arizona and California this year. The bureau also announced it would release an additional 500,000 acre-feet of water from Flaming Gorge reservoir in Wyoming to further raise the water level at Powell.