Colorado
Climate change will reduce streamflow in the upper Colorado river basin as groundwater levels fall, study finds
The Colorado River makes life possible in many Western cities and supports agriculture that sustains people throughout the country. Most of the river’s water begins as snowmelt from the mountainous watersheds of Colorado, Utah, and Wyoming, and a warming climate will drastically reduce these streamflows, new research finds.
Researchers from Desert Research Institute (DRI), USGS, and Lawrence Berkeley National Laboratory teamed up for the new study, published May 23 in Nature Water.
By applying warming to historical conditions for the East River in Colorado and using computer simulations to observe the impact on streamflow and groundwater levels, the scientists found that groundwater storage would fall to the lowest known levels after the first extremely dry year and fail to recover even after multiple wet periods. When groundwater levels fall, streamflows are drawn into the water table instead of contributing to Colorado River flows.
“We found that groundwater matters a lot,” says Rosemary Carroll, Ph.D., DRI research professor of hydrology and lead author of the study. “Even with historically observed wet periods in the model, the groundwater can’t come back from a single dry water year under end-of-century warming.”
The Colorado River has been in a drought state for decades, creating tensions around water rights throughout the Southwest. Scientists have been perplexed by falling river levels even in relatively wet years—in 2021, the Upper Colorado River Basin reached 80% normal snowpack but delivered only 30% of average streamflow to the river.
The study authors wanted to examine how warming in mountain basins may be contributing to this phenomenon. Increased temperatures alter the balance between snowfall and water availability in a number of ways, including more snow evaporation (known as sublimation), more precipitation falling as rain instead of snow, and more frequent melting throughout the winter.
Past research has largely overlooked the role of groundwater and how it may buffer, or intensify, streamflow loss from climate change.
“I’m very interested in the relationship of groundwater contributions to streamflow—that has been a running theme in my research for a long time,” Carroll says. “A lot of studies indicate that in the short term, groundwater release to streamflow will help buffer drought impacts, but before this study, we didn’t have any knowledge on what that would mean over the long haul.”
The study authors used the East River as the focus for the research because it is representative of the headwaters of the Colorado River, as well as the significant weather and water monitoring infrastructure available. Ground observations and airborne mapping measure snowpack depth and density, streamflow, plant cover, and groundwater levels, among many other measurements throughout the watershed.
Historical data from 1987 to 2022 was used to create the computer model. The research team then applied 4 degrees Celsius of warming to this time period in two ways: for one simulation, warming was applied constantly across time, while in subsequent simulations, warming was applied to each season independently.
The approach allowed the scientists to examine the differing impacts of warming between seasons. Four degrees Celsius is representative of the projected climate at the end of the century based on observed warming of approximately 0.4 degrees Celsius per decade in the watershed. The simulation doesn’t account for likely changes in vegetation over the same timeframe.
The study showed that consistently warmer temperatures resulted in sharp declines in groundwater levels that were unable to recover to historical average levels during wet periods. Isolating the warming seasonally demonstrated the strong impact of warmer summers on water table declines, as the atmosphere increases evaporation rates, plants increase their water uptake, and soils dry out. The largest declines in water table elevations occur in the subalpine forests where conifer forests are most dense.
“As the groundwater level drops, you lose more streamflow to the water table,” Carroll says. “When precipitation is low, the East River stops flowing for a portion of the summer. Of course, this would have dramatic effects on ecological health and agricultural irrigation.”
By including declining water table levels in the analysis, the study found that streamflow reductions nearly double when compared to simulations that examined the impacts of climate change in the region without accounting for groundwater declines. This is because of the multiple impacts occurring simultaneously: less water flows to streams from the aquifers, while more stream water drains into the soil.
The research demonstrates the need to jointly manage forest and groundwater in the Upper Colorado River Basin, as well as account for the exchange of surface and groundwater in mountain basins, to minimize streamflow declines under climate change, Carroll says.
“I think of groundwater as your savings account,” she adds. “Snowpack is like your checking account; it changes from year to year. Groundwater is a longer-term investment—it can smooth out the really wet and dry years. But if you start consistently reducing that groundwater year after year, then you can no longer modulate those extremes.”
More information:
Declining Groundwater Storage Expected to Amplify Mountain Streamflow Reductions in a Warmer World, Nature Water (2024). www.nature.com/articles/s44221-024-00239-0
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Climate change will reduce streamflow in the upper Colorado river basin as groundwater levels fall, study finds (2024, May 23)
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Colorado
Colorado residents face earliest water restrictions ever — a harbinger of worse to come
As a result of a snow drought and a heat wave that have both set records, some Colorado residents face the earliest restrictions on their water use ever imposed.
Denver Water announced Wednesday that it is seeking a 20% cut in water use, asking people to turn off automatic watering systems until mid-May and restricting the watering of trees and shrubs to twice a week.
“The situation is quite serious,” said Todd Hartman, a spokesperson for the utility. “We’re in such a dire situation that we could be coming back to the public in two or three months and saying you’re limited to one day a week.”
It is the earliest in the year that Denver Water has ever issued a restriction, Hartman said.
Colorado’s snowpack peaked at extremely low levels on March 12 — nearly a month earlier than usual — then cratered during the recent heat wave that cooked nearly every state in the West.
“We already had the lowest snowpack we’ve seen since at least 1981, and now, with the heat wave conditions, we’ve already lost about 40% of the statewide snowpack” since the March 12 peak, said Peter Goble, Colorado’s assistant state climatologist. “Conditions are looking more like late April or early May.”
The water restrictions are a harbinger of what’s to come in many Western states as officials try to manage widespread drought concerns. Nearly every snow basin in the Mountain West had one of its warmest winters on record and is well behind normal when it comes to water supply, according to the U.S. drought monitor. The dwindling snowpack is likely to raise the risk of severe wildfires, hamper electricity generation at hydropower dams and force water restrictions for farmers.
Hartman said nearly every community east of the Rockies, along Colorado’s front range, is in much the same boat as Denver.
City Council members in Aurora are considering similar water restrictions; reservoirs there stand at about 58%, according to the city’s website. In the town of Erie, officials declared a water shortage emergency on March 20 after they observed a massive spike in consumption.
Gabi Rae, a spokesperson for the town, said Erie was perilously close to having taps run dry because so many residents had started watering their lawns early amid the unseasonable heat.
“We were a day away from running out of water. That’s why it was such an emergency,” she said.
Erie officials demanded that residents stop using irrigation systems altogether.
Goble said this month’s heat wave has set records in every corner of Colorado, sometimes by double digits.
“I can’t remember seeing a single heat wave that broke this many records, and seeing it across such a large portion of the country is certainly eye-popping,” he said, adding: “I’m located in Fort Collins, and we got up to 91 last Saturday. The previous record for March was 81, so we smashed that record. And it wasn’t just one day, either.”
Denver Water, which serves about 1.5 million residents in the city and its surrounding suburbs, gets about half of its water from the Upper Colorado River Basin and the South Platte River Basin. The latter’s snowpack was at about 42% of normal Tuesday, the utility reported. The Upper Colorado River Watershed was at 55%.
Systemwide, Denver Water’s reservoirs are about 80% full, which is only about 5 percentage points lower than in a typical year.
“That sounds pretty good,” Hartman said. “Except that what we’re not going to be able to rely on is that rush of water that will bring those reservoirs back up, because the snowpack is so low.”
In other words, the snowpack — a natural water reservoir — is mostly tapped already and won’t replenish reservoirs later this spring and into summer, when runoff usually peaks.
In Erie, city workers plan to aggressively police water use until sometime next week using smart meters that monitor residential usage. Rae said the city is also sending utility workers to patrol neighborhoods and look for sprinklers that are turned on.
“People have been kind of annoyed with how aggressive we were, and I don’t necessarily think they understand the ramifications if we weren’t,” Rae said. “It is an actual serious emergency situation. We were so close to reaching empty, there would literally be no water coming out of the taps — hospitals, schools, fire hydrants, your home would have no water.”
Although the limits on outdoor watering will be lifted soon, Rae expects more restrictions later this spring and summer.
Colorado
Suddenly hazy skies in Denver prompt some residents concerned about wildfire smoke to call 911
Some people who live in the Denver metro area on Thursday afternoon were making calls to 911 after skies became noticeably hazy and winds kicked up. It was due to smoke from wildfires in Nebraska moving into Colorado. A cold front also was moving through the Front Range, and there is dust in the air.
The poor air conditions led to reduced visibility downtown after 3 p.m. Several of CBS Colorado’s City Cams showed dust or smoke in the air.
Temperatures were expected to drop by as much as 20 to 30 degrees with the cold front.
The suddenly dusty skies prompted at least one fire agency to put out a plea to residents to please only call 911 “if you see flames.” That warning was put out by South Metro Fire Rescue, which shared a photo on X of an office building with haze visible outside.
South Metro Fire Rescue said in their post that the smoke is from Colorado’s neighbor to the east. They called it a “significant haze” in the air.
Earlier this month, the Morrill Fire and the Cottonwood Fire burned a significant amount of Nebraska grassland and ranchland. They have mostly been contained by firefighters. Nebraska Gov. Jim Pillen said those two fires combined with several others have burned approximately 800,000 acres of land. On Thursday, Pillen announced that he is signing several executive actions intended to ease the burden caused by the fires.
There were no wildfires burning in the Denver metro area on Thursday afternoon.
Colorado
Colorado homicide suspect wanted in fentanyl-related death arrested in Colombia
ARAPAHOE COUNTY, Colo. (KKTV) – A homicide suspect based out of Colorado, wanted in a fentanyl-related death, is back in the state after being captured in Colombia.
The Arapahoe County Sheriff’s Office (ACSO) said 33-year-old Max Arsenault had been on the run since January 17.
Deputies said this stemmed from an incident in May 2023, where deputies responded to a call for a man named Nicholas Dorotik, who was found unresponsive.
ACSO said the cause of death was a mixed drug overdose involving meth and fentanyl, having about three times the lethal amount of fentanyl in his system.
One year later, Arsenault was arrested. He was scheduled for trial in January 2026 when deputies said he fled the country while on bond three days before the trial was set to start.
He was caught in Medellin, Colombia, on March 4, following a two-month international investigation. He has since been extradited back to Denver, where he is facing charges and awaiting trial.
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