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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DENVER — Authorities issued a Medina Alert Sunday following a hit-and-run crash that seriously injured a motorist.
Police said the driver of a gold 2008 BMW X3 SUV struck another vehicle at the intersection of Sheridan Boulevard and W. 17th Avenue in Denver around 4:37 p.m. Saturday.
The crash left the driver of the victim vehicle with serious bodily injuries, according to the Colorado Bureau of Investigation.
CBI
The BMW driver fled following the crash, traveling northbound on Sheridan Boulevard, CBI said in a bulletin.
The gold BMW X3, with Colorado license plate ECB F17, sustained heavy damage on the driver’s side from the collision.
If seen, call 911 or the Denver Police Department at 720-913-2000.
This was the second hit-and-run crash and Medina Alert in Denver on Saturday.
Earlier Saturday, a pedestrian in a crosswalk was seriously injured after being struck by a 2010 white Toyota Corolla, Colorado license plate EDM U42, at the intersection of Federal Boulevard and W. Kentucky Avenue.
The driver of the Corolla left the scene—heading northbound on Federal Boulevard.
No arrests have been announced.
A Medina Alert honors the memory of Jose Medina, a 21-year-old valet driver who was killed by a hit-and-run driver in 2011.
A taxi driver witnessed the event, followed the driver, and gave the police the license plate number, leading to the capture and arrest of the suspect.
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Next week is the annual gathering of “water buffaloes” in Las Vegas. It’s the Colorado River Water Users Association convention. About 1700 people will attend, but probably around 100 of them are the key people—the government regulators, tribal leaders, and the directors and managers of the contracting agencies that receive Colorado River water.
Anyone who is paying attention knows that we are in critical times on the river. Temporary agreements on how to distribute water during times of shortage are expiring. Negotiators have been talking for several years but haven’t been able to agree on anything concrete.
I’m just an observer, but I’ve been observing fairly closely. Within the limits on how much information I can get as an outsider, I’d like to propose some principles or guidelines that I think are important for the negotiation process.
See also
- When Hoover Dam was proposed, the main debate was over whether the federal government or private concerns would operate it. Because the federal option prevailed, water is delivered free to contractors. Colorado River water contractors do not pay the actual cost of water being delivered to them. It is subsidized by the U.S. government. As a public resource, Colorado River water should not be seen as a commodity.
- The Lower Basin states of Arizona, California, and Nevada should accept that the Upper Basin states of Colorado, New Mexico, Utah, and Wyoming are at the mercy of Mother Nature for much of their annual water supply. While the 1922 Colorado River Compact allocates them 7.5 million acre-feet annually, in wet years, they have been able to use a maximum of 4.7 maf. During the long, ongoing drought, their annual use has been 3.5 maf. They shouldn’t have to make more cuts.
- However, neither should the Upper Basin states be able to develop their full allocation. It should be capped at a feasible number, perhaps 4.2 maf. As compensation, Upper Basin agencies and farmers can invest available federal funds in projects to use water more efficiently and to reuse it so that they can develop more water.
- Despite the drought, we know there will be some wet years. To compensate the Lower Basin states for taking all the cuts in dry years, the Upper Basin should release more water beyond the Compact commitments during wet years. This means that Lake Mead and Lower Basin reservoirs would benefit from wet years and Lake Powell would not. In short, the Lower Basin takes cuts in dry years; the Upper Basin takes cuts in wet years.
- Evaporation losses (water for the angels) can be better managed by keeping more of the Lower Basin’s water in Upper Basin reservoirs instead of in Lake Mead, where the warmer weather means higher evaporation losses. New agreements should include provisions to move that water in the Lower Basin account down to Lake Mead quickly. Timing is of the essence.
- In the Lower Basin states, shortages should be shared along the same lines as specified in the 2007 Interim Guidelines, with California being last to take cuts as Lake Mead water level drops.
- On the home front, IID policy makers should make a long-term plan to re-set water rates in accord with original water district policy. Because IID is a public, non-profit utility, water rates were set so that farmers paid only the cost to deliver water. Farmers currently pay $20 per acre foot, but the actual cost of delivering water is $60 per acre foot. That subsidy of $60 million comes from the water transfer revenues.
- The SDCWA transfer revenues now pay farmers $430 per acre-foot of conserved water, mostly for drip or sprinkler systems. Akin to a grant program, this very successful program generated almost 200,000 acre-feet of conserved water last year. Like any grant program, it should be regularly audited for effectiveness.
- Some of those transfer revenues should be invested in innovative cropping patterns, advanced technologies, and marketing to help the farming community adapt to a changing world. The IID should use its resources to help all farmers be more successful, not just a select group.
- Currently, federal subsidies pay farmers not to use water via the Deficit Irrigation Program. We can lobby for those subsidies to continue, but we should plan for when they dry up. Any arrangement that rewards farmers but penalizes farm services such as seed, fertilizer, pesticide, land leveling, equipment, and other work should be avoided.
- Though the IID has considerable funding from the QSA water transfers, it may need to consider issuing general obligation bonds as it did in its foundational days for larger water efficiency projects such as more local storage or a water treatment plant to re-use ag drain water.
Much progress has been made in using water more efficiently, especially in the Lower Basin states, but there’s a lot more water to be saved, and I believe collectively that we can do it.
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