The snowy winter in the Rockies may not mean enough runoff to refill the Colorado River
The beleaguered river continues to struggle with climate change and an imbalance between supply and demand.
Recent data shows a snowy start to 2023 for the Colorado River basin, with heavy winter precipitation in the Rocky Mountains projected to increase spring and spring runoff into Lake Powell to 117% of average annual runoff.
However, scientists say that while this winter’s snow may temporarily boost major reservoirs, it will not provide enough water to address the Southwest’s long-term supply-demand imbalance as the beleaguered river continues to cope with climate change and steady demand has fight.
Snow in Colorado is an important factor in determining the amount of water that will flow into the Colorado River system each year. About two-thirds of annual flow begins as snow high in the Colorado mountains. Snow levels across the state are almost all above average, with most zones averaging 120-140% of normal for this time of year.
Northwest Wyoming and central Utah, which also contribute to the basin’s water supply, saw January snowfalls that nearly broke rainfall records. Many parts of Utah experience snow levels in excess of 170% of average, increasing the likelihood of above-average spring discharge and making for unforgettable seasons at the region’s ski resorts.
The new data comes from the Colorado Basin River Forecast Center, a branch of the National Weather Service that tracks water along a river that serves 40 million people in the Southwest.
The upper Colorado River basin — which includes parts of Wyoming, Colorado, Utah and New Mexico — saw the heaviest rainfall in southwestern Colorado, according to last month’s data. The Gunnison, Dolores, and San Juan rivers saw rainfall in January ranging from 160% to twice the average. Meanwhile, the lowest rainfall totals in January were along the Eagle River in central Colorado and the Green River above Wyoming’s Fontenelle Reservoir.
The Lower Colorado River Basin — which includes parts of Nevada, Arizona and California — also saw heavy rainfall. The Virgin, Little Colorado and Verde rivers recorded rainfall in excess of 200% of normal in January. Rain and snow in the Lower Basin are typically less important to Colorado River flow, but are helpful for crops, farms and ranches, and wildfire containment.
The precipitation totals “are exceeding expectations because La Nina conditions typically result in dry-than-average winter weather in the US Southwest,” said Cody Moser, hydrologist for the Colorado Basin River Forecast Center.
La Niña is a weather phenomenon in which cold Pacific Ocean waters alter temperature and precipitation patterns over the western United States. Its impact is not guaranteed, but typically means a colder, wetter winter for the north-western part of the country and a warmer, drier winter for the south-west. The dividing line is often in the middle of Colorado.
When it comes to predicting the amount of water in the Colorado River each year, snow totals don’t tell the whole story. Scientists look at soil moisture to get a clearer picture of how much water is actually reaching the places where people are diverting and collecting it.
This year, the soil moisture in the mountains is well below average. That could prevent melting snow from ever reaching the Colorado River. This soil acts like a sponge, soaking up water before it can flow downhill into streams and lakes. Scientists have recorded years with 90% of the average snow cover only to see 50% of the average runoff in reservoirs.
Even the concept of “average” has changed due to warming. In spring 2021, the National Oceanic and Atmospheric Administration changed the way it calculates averages for all of its data.
Every 10 years, NOAA moves the three-decade window it uses for averages. But the rapidly accelerating effects of climate change mean the current 1991-2020 window stands out from previous 30-year periods because it encompasses the hottest period in recorded history.
The runoff season typically peaks in late May or early June. These rivers replenish Lake Mead and Lake Powell — the largest and second-largest reservoirs in the United States, respectively — both of which have fallen to historic lows in recent years. Two decades of low snow and dry soil have impacted water supplies, and the seven states that use the Colorado River are struggling to agree on a plan to reduce their needs.
Climate scientists emphasize the need to adjust demand to match current conditions and prepare the region for a future that is likely to bring even drier conditions. Brad Udall, a water and climate researcher at Colorado State University, said it would take the region five or six years with 150% snow cover to refill Lake Powell and Lake Mead
“We must continue to assume the worst here,” Udall told KUNC in January. “We’ve seen that in the last 23 years. That’s what these warming temperatures continue to tell us.”
– This story is part of ongoing Colorado River coverage produced by KUNC in Colorado and supported by the Walton Family Foundation. KUNC is solely responsible for editorial reporting.
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https://www.sltrib.com/news/nation-world/2023/03/08/rockies-snowy-winter-may-not-mean/ The snowy winter in the Rockies may not mean enough runoff to refill the Colorado River