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DRI Science On the Colorado River
A selection of DRI research supporting Colorado River water management
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The Colorado River Basin, with hatched areas outside of the boundary receiving Colorado River water via inter-basin transfers (also known as ‘exports’). Credit: Richter et. al, 2024
The Colorado River is a central part of life in the American West. This national artery supplies water to seven states and parts of northern Mexico, with 40 million people relying on it to keep their taps flowing and nearly the entire country (and beyond) depending on food grown with the river's water. Managing this water responsibly has become a growing challenge, with the region experiencing a historic drought and climate change reducing the predictability of precipitation in the river's headwaters. With less snow falling in the mountains and drier weather pulling more of the river's water back into the atmosphere, scientists and water managers strive to better understand every aspect of the river's water cycle. Researchers at Nevada's Desert Research Institute (DRI) are leading the way in several fields, from the river's Rocky Mountain source down to the Mexican border.
Legally binding agreements about how to divide up the river's water were made more than a century ago, and demand now outpaces supply. In the Lower Basin alone (see map to the right), the river faces a deficit large enough to fill half a million Olympic-size swimming pools, imperiling the river's reach to the Gulf of California. The stretch of the river that carves through the Grand Canyon—one of the most iconic American scenes—has also been declared the nation's most endangered river .
This graphic shows how Colorado River water is allocated between seven U.S. states and Mexico, with Nevada receiving the smallest share.
The river's challenges are well known, but the scientific and technological advancements that will help chart a sustainable path forward are another critical element of the river's legacy. As climate change and human population growth require scientific ingenuity to maintain our standard of living in the West, the advancements produced will offer solutions to regions worldwide that are likely to face similar challenges.
"It often feels like we're at the sharp end of the stick when it comes to climate change," says Sean McKenna , Director of DRI's Division of Hydrologic Sciences . "A lot of the things we're experienced in dealing with now in the southwestern U.S. will become more common in other parts of the country—and the world—moving forward."
This Storymap offers an overview of some of DRI's research related to the Colorado River, much of which is focused on finding solutions for a changing world. With advancements in fields like estimating evaporation off of reservoirs, creative ways to supplement and protect mountain snowpacks, and using satellites to measure vegetation water use, the research presented here is an example of science's value for guiding humanity to a brighter future.
Colorado's East River in the winter, covered in the snow that will become the Colorado River's water.
Finding Missing Water
Examining how climate change is altering the water balance at the headwaters of the Colorado River
When clouds meet the soaring peaks of the Rocky Mountains, their moisture condenses into snow and falls to Earth. When snowmelt fills the streams and rivers that feed the Colorado River's tributaries such as the East River, pictured here, the river's 1,400 mile journey begins. But much less visibly, it also seeps into soils and replenishes groundwater aquifers, sustaining plants through the dry season and feeding groundwater springs.
Understanding the nature of this water balance—and how it is changing with the warming climate—is key to forecasting water availability in the West. With the country's reliance on it for sustaining communities of millions and growing food for dinner plates nationwide, the focus is perhaps greatest on the Colorado River.
DRI's Rosemary Carroll is a Research Professor of Hydrology who studies connections between climate change, snowpack, and groundwater from her home in Crested Butte, Colorado. She's focused much of her work on this part of the river's headwaters since 2006.
Carroll's work seeks answers to some of hydrology's biggest questions, such as how vegetation impacts stream flow and where stream water is sourced from. She uses stable isotope analysis to trace the ratio of stream flows that originated as rain or snow, and can even trace the elevation of the snowfall that produced the snowmelt. Stream chemistry, water isotopes, and radon measurements are also used to trace stream flows back to groundwater , showing that late summer streams in the area are flowing largely due to available groundwater. This underscores the findings of a recent study , led by Carroll, that found rising temperatures will impact water in the region in a number of ways.
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, Carroll and her team 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.
The graphic above illustrates how declining water tables under climate change would decrease streamflows. Click to expand
“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.”
The study could help explain perplexing drought conditions in the Upper Colorado River Basin; in 2021, the Upper Basin reached 80% normal snowpack but delivered only 30% of average streamflow to the river.
The mountains surrounding Crested Butte are an ideal location for studying changes to the region's snowpack, Carroll says, because of the concentration of science conducted here. As home to the Rocky Mountain Biological Laboratory (RMBL), instrumentation and scientific creativity abound. The mountains here are also changing faster than lower elevations, offering insight for the future—"like the canary in the coal mine," she says.
As an expert hydrologist on location, Carroll collaborates with researchers from RMBL, SLAC National Accelerator Laboratory, Lawrence Berkeley National Lab, and numerous other universities and institutions. When the Airborne Snow Observatory is collecting aerial LiDAR data to measure the basin's snowpack, Carroll is digging snowpits to ground-truth their results. She helps manage a series of sensors throughout the basin that measure air and soil temperature, humidity, snowpack, and stream flow that feed her modeling work and add to the area's scientific ecosystem.
A mountain weather monitoring station.
For all of her time conducting research, Carroll says that some of her most meaningful and insightful work comes from her position on the board of the Upper Gunnison River Water Conservancy District. In this voluntary role, she acts as a scientific translator and intermediary who can help make sure that the concerns of local ranchers and other stakeholders are being heard.
Although the language used by scientists often differs from that of the locals, "Water can be a unifier," she says. "We're all working toward the same goal."
"In fact, my science is improved by listening to them, because when I hear what they're concerned about, I can then think about the questions I want to ask based on my conversations with them."
One example is ranchers' drought concerns surrounding soil moisture, as it directly impacts crops and the availability of feed for livestock. Soil moisture is a critical component of the water balance, Carroll says, because it's the link between the surface and the subsurface. Sometimes discussing specific concerns like soil moisture can help scientists make climate change research more tangible.
"The more I talk to ranchers, the more I realize that there’s always another point of view and scientists can do better and more impactful science if we listen,” she says.
Watch this short video to learn more about Rosemary Carroll's work studying connections between climate change, snowpacks, and groundwater at the headwaters of the Colorado River.
A DRI cloud-seeding generator in Winter Park, Colorado.
Supplementing the Snowpack
DRI's long-standing cloud-seeding program works to enhance precipitation throughout the Rocky Mountains of Colorado, feeding the source of the Colorado River. For decades, our team has operated ground-based cloud-seeding generators that enhance natural snowstorms by introducing additional ice nuclei to passing storm clouds. The method can increase a targeted region's snowpack by around 10% over the course of the winter.
“I feel really passionate that we can improve water resources across the Western U.S. with these cloud-seeding programs,” said Frank McDonough , DRI’s cloud-seeding program director. “And we can run them relatively inexpensively. It’s really the only way to add precipitation to a watershed.”
To enhance snowfall, a meteorologist carefully monitors incoming storms for ideal conditions. When a storm with sufficient super-cooled liquid water arrives, and the winds are primed to carry snowfall to the targeted area, the generators are activated. A propane tank supplies the fuel to a flame that vaporizes silver iodide directly into the passing storm. The silver iodide provides the cloud's moisture with the central particle it needs to converge on to form an ice crystal, supplementing the dust particles provided by nature that form the center of every snowflake you've ever seen.
A DRI cloud-seeding generator vaporizing silver iodide into a passing cloud. Credit: Jesse Juchtzer
The map to the left shows the locations of cloud-seeding generators operated by DRI (red dots) and those that DRI produced for the State of Colorado (orange dots). All of DRI's generators are designed and fabricated by our team, and many are distributed to collaborators throughout the Western U.S.
In the winter of 2023-2024, these generators are estimated to have produced over 8 billion gallons of water—enough to supply more than 65,000 homes for a year.
Beyond supplementing the snowpack, cloud-seeding can also help preserve it. By adding fresh, white snow over dirtied snow, cloud-seeding can maintain the snow's natural ability to reflect sunlight and prevent premature melting. With a slower spring and summer snowmelt, the snowpack can continue to fill springs and nourish plant life through the dry summer months.
Click the link below to learn more about the science and history of cloud-seeding:
DRI's cloud-seeding team fabricates the generators by hand in our workshop.
DRI's cloud-seeding program stands out from others operating in the Western U.S. by a rigorous, research-based approach. Our team's work doesn't end after a storm is seeded, as the scientists then work to verify their efforts. Our research program helps advance the science and understanding of cloud-seeding, to the benefit of programs worldwide.
In addition to analyzing precipitation gauges and hydrological records, our scientists also conduct snow chemistry research. The photo to the left shows a DRI scientist in a snowpit, working to collect samples of the snowpack that will be brought to DRI's Reno campus and analyzed in our state-of-the-art Trace Chemistry/Ice Core Laboratory . The snowpack preserves the story of the winter's storms, with visible striations showing layers of wetter or drier storms differentiated by the quality and density of the snow.
An example snowpack sample showing visible layers of snow from different storms.
In the laboratory, the snow samples will be melted down with an instrument that can identify trace amounts of chemicals such as silver iodide. By verifying that the seeding agent is found in the snowpack, the scientists know that their efforts reached the targeted area and added to the storm's precipitation.
Watch this short video to learn more about DRI's cloud seeding program for local precipitation enhancement.
Estimating Reservoir Evaporation
On the other end of the water cycle from precipitation enhancement, DRI has several projects focused on evaporation, or the return of water to the atmosphere in the form of water vapor. A 2022 study led by DRI scientists found that the warming climate is resulting in a "thirstier" atmosphere, one that pulls more water from Earth's plants, rivers, streams, and reservoirs. The team’s findings showed substantial increases in evaporative demand across much of the Western U.S. during the past 40 years, with the largest and most robust increases in the Southwest.
In the Lower Colorado region, the study found that atmospheric thirst increased by 8 to 15 percent between 1980 and 2020. This means that growing the same crop, under the same management, now requires 8 to 15 percent more water than it did 30 years ago.
"This is really important to understand, because we know that atmospheric thirst is a persistent force in pushing Western landscapes and water supplies toward drought," said Christine Albano , Research Professor of Ecohydrology and lead author of the study.
Click the link below to read the full news release about this study:
In an ongoing, long-term collaboration with the Bureau of Reclamation, one project seeks to put numbers to a key question plaguing Colorado River water management: On a river where every drop counts, how much water are we losing to the atmosphere from our reservoirs?
"More water is allocated from the Colorado River than is available, and everyone is arguing about who should take cuts," says Chris Pearson , a DRI hydrologist who leads the effort. "But with increasing evaporation due to climate change, the atmosphere is taking more and more of the actual water supply, further exacerbating the imbalance."
In fact, evaporation from Lake Mead alone amounts to nearly three times the amount of water allocated to Nevada from the Colorado River each year.
On a floating platform in Lake Powell's Padre Bay, Pearson and his colleagues have set up three different systems to estimate evaporation rates. The floating platform allows for the equipment to obtain more accurate data for evaporation over water, where conditions tend to vary from those over land. The research is a technological leap forward from the old method of using a shallow pan of water placed near the reservoir to measure evaporation—a system that often over-estimates evaporation rates, sometimes by up to 50%.
Even with the advanced technology, Pearson stresses that evaporation is a dynamic issue with no single answer—it varies all across a body of water and from one moment to the next. Impacted by factors like wind speed, air temperature, and humidity, researchers can only hope to improve ways for estimating it, not measuring it.
"It's like trying to hit a moving target, but one that is key to understanding just how much water we have available now and into the future," he says.
An eddy covariance system—regarded by scientists as the gold standard for studying evaporation rates—sits alongside an aerodynamic mass transfer system. The two techniques were compared in a 2022 report , while a third technique has since been added: a newer piece of technology developed by LI-COR, the LI-710 Evapotranspiration Sensor . By placing all three systems side by side, scientists can compare accuracy and practicality of deployment in the field. By identifying the most accurate, reliable, and cost-effective sensor system, they hope to make it possible for more reservoirs to deploy their own.
For a detailed explanation of how the eddy covariance and LI-COR systems work, watch this short video clip:
DRI's Chris Pearson showing how the eddy covariance (1) and LI-COR (2) systems work to estimate evaporation off Lake Powell. Click full screen to expand.
The Lake Powell equipment is also providing a way for DRI researchers to validate the ability of remote sensing tools and computer algorithms to estimate evaporation. A new project funded by DRI's role with the NSF Engines: Southwest Sustainability Innovation Engine (SWSIE) is using satellites launched by Hydrosat to estimate reservoir evaporation from space.
The Hydrosat satellites use new thermal infrared technology to collect daily water surface temperature at a higher resolution (~20 meters) than is available from other platforms. That information, when combined with state of the art remote sensing algorithms, can provide estimates of evaporation that DRI will then compare to the data collected at Lake Powell.
The initial project is expected to wrap up in early 2025 and will use the Hydrosat data to evaluate evaporation from several reservoirs across the southwest. Once the process is refined, the team hopes to expand the project to reservoirs nationwide.
Pearson and DRI colleagues are also developing methods to estimate evaporation using climate data like wind, temperature, and relative humidity. This method has been applied to reservoirs across Texas, where stakeholders can now visualize and download data on evaporation rates in near-real time using an interactive portal .
Following the success of the project for Texas reservoirs, the project team is expanding the work to cover every major reservoir in the Western U.S. The project is expected to be completed in 2026.
OpenET: Improving Water Management
But water loss doesn't just happen on reservoirs, so DRI scientists partnered with NASA, Environmental Defense Fund, and other groups to create OpenET . This project utilizes satellite data and advanced computer modeling to measure evapotranspiration (the combination of evaporation and transpiration, or water lost through plant photosynthesis), to improve water management.
OpenET has allowed for the rapid advancement of scientific breakthroughs, particularly for tracking water use on irrigated agriculture—the largest user of Colorado River water. This tool can measure water use in individual fields and track how efficiently crops are using irrigation water, which can help farmers adjust water use to reduce evaporative losses. The project has digitized 40 million agricultural fields across 17 Western states, allowing stakeholders to obtain evapotranspiration losses on a particular field for the previous year (and up to 10 years for some fields).
In a study published in early 2024, DRI scientists led a comparison of OpenET data to evapotranspiration data produced by ground-based eddy covariance flux towers. The research found that OpenET data has high accuracy for assessing evapotranspiration in agricultural settings, particularly for annual crops in arid regions like California and the Southwest, where error rates were consistently below 10%.
“Evapotranspiration is one of the hardest hydrologic fluxes to measure, and to think we are quantifying this flux from space with comparable or better accuracy to ground-based weather stations and meter data for agricultural lands is really remarkable,” said study co-author Justin Huntington , research professor at DRI and member of OpenET's leadership team.
The ability to measure crop water use is particularly valuable in the Colorado River Basin, where nearly 75% of all water used goes to agriculture.
Using OpenET data and soil water balance modeling, DRI scientists recently conducted a thorough analysis of historical water use on irrigated crops in the Upper Basin over the last 3 decades (1991-2022). The report found that the highest water use occurred in 2020, and that agricultural water use grew by about 5 billion gallons each year.
Colorado was found to be the largest overall user of irrigation water, followed by Utah, Wyoming, and New Mexico. However, crops were found to be thirstiest in New Mexico and Utah, with higher average evapotranspiration rates.
Satellite imagery (top) shows the extent of irrigated crops (classified in green in the bottom image) and fallow fields (orange).
Historically, these estimates were created in a simplified way by using temperature, daylight hours, crop type, growing season length, and crop acreage to estimate evapotranspiration. The use of OpenET allows for more real-time, accurate estimates that can lead to improved water management. Importantly, with satellite imagery of the entire basin, the extent of active crops can be viewed and estimated each year, rather than relying on historical maps and snapshots.
With so much of the river's water used to feed the nation, the Colorado River's water shortages come into broader perspective. "It's a national problem," says Sean McKenna , Executive Director of DRI's Division of Hydrologic Sciences. "If you're living in New England and eating vegetables in winter, there's a very good chance you're consuming Colorado River water."
Measuring Microplastics
Scientists in DRI's Microplastics and Environmental Chemistry Laboratory are leaders in the study of this ubiquitous environmental contaminant. From the crystal clear blue waters of Lake Tahoe to the sprawling Mekong River in Cambodia, our researchers strive to measure concentrations and identify the sources of these plastics.
Working with Lab Director and DRI hydrologist Monica Arienzo , graduate student Hannah Lukasik collected Colorado River samples near the Nevada/Mexico border to evaluate microplastic prevalence and compare overall pollution levels to the Truckee River.
By examining more than 2,300 microplastics from 7 sites, Lukasik found that most came from single-use plastics (such as plastic bags or agricultural land cover) and rubber from vehicle tires and brakes. Their prevalence also increased with more discharge from upstream dams.
Lukasik's study helps to identify pollutants that could be impacting the river's ecological health, with tire particles containing chemicals toxic to both wildlife and people . By collecting samples near the Mexican border, she also found that water pollution sourced in the U.S. is making its way into Mexico.
A map of Lukasik's study area in the Lower Colorado River Basin.
About DRI
We are Nevada’s non-profit research institute, founded in 1959 to empower experts to focus on science that matters. We work with communities across the state–and the world–to address their most pressing scientific questions, while building bridges between scientists and policymakers to enact positive change.
We’re proud that our scientists continuously produce solutions that better human and environmental health. We pioneered the use of chemical fingerprinting to identify sources of air pollution in Nevada’s cities and reduce haze in National Parks across the country. We work with communities downwind of historic atomic testing at the Nevada National Security Site to monitor radiation exposure. We used ice trapped below the surface of Greenland to connect historic levels of lead pollution with the rise and fall of ancient economies like the Roman Empire. For decades, we have been using satellite technology to locate, and build, drinking water wells for communities in Ghana and we have enhanced precipitation throughout Nevada, the driest state in the nation, using decades of research on cloud seeding.
Scientists at DRI are involved with students at other Nevada System of Higher Education institutions, offering research positions and teaching support, but are not expected to take on the heavy teaching loads of university professors. Instead, they are encouraged to follow their research interests across the traditional boundaries of scientific fields, collaborating across DRI and with scientists worldwide. We reach thousands of young Nevada students annually with specialized science and robotics lessons and free continuing education for teachers. All faculty support their own research through grants, bringing in nearly $5 to the Nevada economy for every $1 of state funds received. With more than 600 scientists, engineers, students, and staff across our Reno and Las Vegas campuses, we conducted more than $52 million in sponsored research focused on improving peoples’ lives in 2024 alone.
At DRI, science isn’t merely academic – it’s the key to future-proofing our communities and building a better world.