Colorado River Basin aquifers are declining even more steeply than the river, new research shows.
Sarea Hefer
News Article: https://insideclimatenews.org/news/02062025/colorado-river-groundwater-rapid-decline/
Research Article: https://agupubs.onlinelibrary.wiley.com/action
Background:
In this study, they utilize NASA GRACE satellite observations of terrestrial water storage. The Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On are dual-satellite missions monitoring and mapping Earth's changing gravity field. GRACE produced monthly gravity field solutions from April 2002 through June 2017, and GRACE-FO has continued that record from June 2018. This time history has been an invaluable resource for tracking large-scale flooding, droughts, and glacial melting. [2]
Groundwater is one of the most important natural resources. “The United States uses 82.3 billion gallons per day of fresh groundwater for public supply, private supply, irrigation, livestock, manufacturing, mining, thermoelectric power, and other purposes.” [3] In parts of the country where there is no access to surface freshwater, they rely heavily on the groundwater aquifers to sustain their communities.
This study aimed to discuss not only the declining availability of freshwater in the CRB but also the devastating effects that this decline will have on the groundwater in these regions if regulations are not put in place.
Peer-reviewed Article:
This study, titled “Declining Freshwater Availability in the Colorado River Basin Threatens Sustainability of Its Critical Groundwater Supplies,” uses NASA GRACE and GRACE-FO satellite data to quantify long-term groundwater loss in the Colorado River Basin (CRB), a critical water source for seven U.S. states and Mexico. Although all seven states have equal priority under the 1922 Colorado River Compact, Arizona is particularly vulnerable to water shortages because, under the 2007 Interim Guidelines, it faces the largest mandatory reductions in water deliveries when Lake Mead reaches critically low elevations. The Colorado River Basin is experiencing aridification due to both anthropogenic and natural causes.
In this study researchers analyzed over two decades (2002-2024) of satellite data in order to estimate the overall changes in the TWS trends, including snow, soil moisture, surface water, and groundwater. For this analysis three GRACE/FO mascon solutions were used: NASA Jet Propulsion Lab, The University of Texas Center for Space Research and NASA Goddard Space Flight Center. The change in water storage over time was then calculated based on both liquid and solid precipitation, total evapotranspiration, and total runoff. The data used in the analysis did not include seasonal patterns. This was done so that the analysis would focus only on the overall trend instead of being influenced by short-term, seasonal ups and downs. This non-seasonal time series was used to estimate the amount of water lost in the basin. These analyses were conducted in three parts in order to gain a more comprehensive understanding of the picture within the basin. They conducted analysis on both the upper and lower Colorado River Basins and then one on the Colorado River Basin as a whole rather than just summing the two.
As shown in the figure, the entire Colorado River Basin experienced terrestrial water storage loss.
The study found that the CRB lost a total of 52.2 ± 4.0 km³ (42.3 million acre-feet) of water over the study period, with groundwater accounting for 65% (34.3 ± 9.2 km³) (27.8 million acre-feet) of this loss. The Upper Basin lost 14.6 ± 3.5 km³ (53% groundwater), while the Lower Basin lost 36.0 ± 6.2 km³ (71% groundwater). [1] This groundwater depletion was most severe in areas with heavy agricultural reliance and limited access to surface water. And there was a larger loss in the LCRB due to higher seasonal precipitation intensity in the UCRB and a higher elevation leading to more snow in the UCRB.
This uneven distribution can also be attributed to the need for pumping groundwater in the LCRB in order to support irrigation for agriculture; approximately 80% of the CRB's water is used for irrigation, supporting a $1.4 billion agricultural industry in Arizona alone.
Although Arizona, the state most likely to take the brunt of the hit as surface water is declining, has implemented a groundwater management act which has slowed losses in certain Active Management Areas (AMAs), only 18% of the state is covered by such regulations, leaving most of the basin unprotected.
The study calls for including groundwater in interstate Colorado River agreements and for stronger federal oversight to ensure long-term sustainability of groundwater. The findings reveal that groundwater is the dominant driver of long-term water loss in the basin. Without reduced extraction and comprehensive management, continued depletion threatens agriculture, urban supply, and regional economies.
News Article:
The news article titled “Colorado River Basin Aquifers Are Declining Even More Steeply Than the River, New Research Shows” and written by Wyatt Myskow examines new research on groundwater depletion across the Colorado River Basin. The article translates the technical findings of the paper into a discussion on policy as it emphasizes the urgency of state-level accountability. The article highlights the ongoing negotiations among the seven basin states over reduction in surface water use, noting Arizona as the state expected to be hit the most. However, these negotiations are only over surface water, as it is regulated federally, whereas groundwater is regulated at the state level. Myskow summarizes the findings of the study, which reveal that groundwater losses are now outpacing the river’s surface water declines, with the basin losing tens of millions of acre-feet over the past two decades. The article emphasizes that “... it is known that surface water supplies and aquifers are often interconnected, meaning impacts to one affect the other. Despite that, only surface water is collectively managed by the federal government and the states.” [4] Due to the interconnectedness of these resources, the news article concludes by urging state leaders to keep in mind the losses of groundwater as they try to implement the new cuts to surface water use across the seven states.
Analysis:
Overall I would rate this article a 9/10. I felt that the author presented the major findings of the study well and in a way that made it easily relatable to the reader. While the scientific paper focuses on quantifying total water loss using satellite data, the news piece highlights the political challenge of managing shared water resources without coordinated groundwater policy. The author of the paper was interviewed and quoted in the article in a way that further clarifies the more nuanced parts of the paper. The news article also brought in several other sources that were not a part of the paper, such as the Bureau of Reclamation, to provide a look to the future that was not present in the paper, as well as Professor Koebele for her insights on the interconnectedness of the water supplies in the Colorado River Basin. The only reason I took off a point is because I did not feel that the article gave an idea of what comes next for the everyday reader; rather, it focused more on what the state legislators needed to do in order to prevent further damage. It gave the reader bad news without a suggestion on what they could do to help. The author did an excellent job of summarizing the major findings of the paper as well as elaborating on the political background of these findings and how they should be used to make policy changes.
Sources:
Abdelmohsen, K., Famiglietti, J. S., Ao, Y. Z., Mohajer, B., & Chandanpurkar, H. A. (2025). Declining freshwater availability in the Colorado River Basin threatens sustainability of its critical groundwater supplies. Geophysical Research Letters, 52(10). https://doi.org/10.1029/2025gl115593
Croteau, M. J. (n.d.). About the Mascon Visualization Tool. Mascon Visualization Tool. https://ccar.colorado.edu/grace/about.html
Groundwater: Groundwater facts. Default. (n.d.). https://www.ngwa.org/what-is-groundwater/About-groundwater/groundwater-facts
Myskow, W. (2025, September 20). Colorado River Basin aquifers are declining even more steeply than the river, new research shows. Inside Climate News. https://insideclimatenews.org/news/02062025/colorado-river-groundwater-rapid-decline/
Hi Sarea! Thank you for your analysis and for sharing this interesting article with us.
ReplyDeleteI agree that the news article was very helpful in clarifying many parts of the main study (based on your analysis of it, since I couldn’t open the news article without a subscription). I understood the study much better after reading your explanation of the news article - for example, the point that surface water is regulated federally while groundwater is regulated at the state level. I didn’t realize that until the end. However, I am also not sure how federal regulation of the basin water, rather than state-level regulation, could prevent it from drying out, unless we do something more dramatic to address climate change as a whole.
I have two questions:
1. I understand that Terrestrial Water Storage (TWS) includes all water storage, but I am curious how analyzing TWS trends helps the researchers determine the contribution of groundwater loss in the basin.
2. Also, the article mentions that satellites such as GRACE tracks groundwater and soil moisture. Could you please explain how a satellite can measure water that is below the surface?
Thank you!
Hi Frozan! Thank you for your insightful comments and questions. To address your first question about how the TWS helps the researchers to determine the contribution of groundwater loss, the researchers used the satellite observations combined with land surface models as well as direct measurements from on location to quantify the groundwater depletion in the CRB. As far as the second question, the GRACE satellites measure tiny changes in the Earth’s gravitational field caused by shifts in the Earth's mass, with water being the major factor in these mass shifts. By tracking these changes, scientists create maps of changes in Earth’s gravity field which primarily reflects variations in the TWS. To link the two, satellites “weigh” the water from space by sensing the changes in gravity and in order to distinguish between surface water, soil moisture, and deep groundwater the scientists use GRACE data as well as ground observations and some precipitation data to effectively estimate the amount of water that is a part of each of these facets of TWS.
ReplyDeleteHi Sarea! Thanks for your insightful discussion of these articles. I hadn't realized that groundwater is regulated at the state level, rather than the federal level. I definitely agree that the other sources brought in by Myskow help provide broader context for the scientific findings, which is especially helpful given the technical nature of the research. I particularly like that both the news and scientific articles are very clear about the importance of groundwater reservoirs and the need to understand these resources, because the science here is shedding light on a serious problem. I've learned previously that groundwater (and water resources more generally) are hard to regulate not only because the water crosses political boundaries, but also because knowing how much water is being used by different stakeholders is a challenge, particularly if the inputs and outputs of a reservoir or river aren't fully mapped. Do you think that the findings of the scientific article provide any insight into how we can better monitor and manage groundwater? Or have you come across specific regulatory/management actions suggested by other sources?
ReplyDeleteThank you so much for your comment, I agree that the clarity of both the article and the peer reviewed paper is important for understanding the importance of this research. I liked your insight on the challenges that come with regulating water resources, it it one of those resources that is hard to directly pin down. What I liked about the article was the acknowledgement that specifically in the CRB the seven states that rely on it have a counsel to come together and discuss what they believe to be the best allocation of resources given the decline in the surface water. As far as your questions about how to better monitor and manage groundwater, I believe that a federal push to keep up to date on the monitoring of the sources of groundwater might lead to more regulation at the state level, mostly because they would be forced to have that sort of awareness. I have not come across any specific management actions but I think it starts with studies like these bringing awareness to the people and the state governments that are currently in charge of this regulation.
DeleteThank you for such an insightful blog post! Prior to today I had never heard of the Colorado River Basin, and was unaware of how much groundwater contributed to it. I am curious, though, about the data not considering seasonal patterns. I'm assuming that they were able to normalize the data so that annual fluctuations were accounted for as a part of the baseline, but I'd love to know if you have any more insight into it. I am also curious as to the anthropogenic and natural causes that may have been listed as contributors to the continuous depletion of groundwater in the region. I agree with your judgement on the news article; I also appreciate that they mentioned the political jurisdictions involved in making change on a policy level, but I concur that a call to action for the average reader would also be a beneficial addition.
ReplyDeleteThank you for your comment, I apologize for not making this better know in the post but all of the data was normalized using the Seasonal-Trend decomposition based on LOESS, which include the following steps: (a) filling in the missing months by utilizing linear interpolation, (b) applying STL decomposition to separate seasonal and trend components, and (c) extracting the nonseasonal (trend) component from the non-gap-filled time series. As far a the contributors to the depletion the largest ones they mentioned were climate change and agriculture.
ReplyDelete