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Title	Date	Authors	Cite	Abstract
Decelerating Response of Western US Runoff to Shrinking Snowpacks	2025-05-16	Ban et al.	Ban, Zhaoxin, Brad Udall, and Dennis P. Lettenmaier. “Decelerating Response of Western US Runoff to Shrinking Snowpacks.” Geophysical Research Letters 52, no. 9 (May 16, 2025): e2025GL114629. https://doi.org/10.1029/2025GL114629.	Climate warming threatens snowmelt‐derived water supplies in the western US (WUS) by reducing snowfall and snowmelt runoff, yet future rates of these declines remain highly uncertain in an evolving climate. Here, we analyze historical data, land surface model warming experiments, and climate projections across three major WUS river basins. We find that runoff loss become less sensitive to warming as snowpack shrinks, stemming from reduced snowmelt‐radiation feedback, a consequence of smaller snow‐cover changes and shifts in snowmelt timing to lower‐energy periods. Near‐linear projected warming with time (IPCC SSP245) exhibit a stable, possibly decelerating decline in runoff ratios. Although decelerating runoff declines do not eliminate broader water‐management challenges under continued warming, our findings complement the view that snowmelt‐radiation feedback drives runoff decline by highlighting the negative feedback from a shrinking snowpack on runoff warming sensitivity. Our findings should facilitate more comprehensive future water supply assessments in snow‐affected regions.
Multidecadal drought impacts on the Lower Colorado Basin with implications for future management	2025-03-18	Scanlon et al.	Scanlon, Bridget R., Donald R. Pool, Ashraf Rateb, Brian Conway, Kathryn Sorensen, Bradley Udall, and Robert C. Reedy. “Multidecadal Drought Impacts on the Lower Colorado Basin with Implications for Future Management.” Communications Earth & Environment 6, no. 1 (March 18, 2025): 214. https://doi.org/10.1038/s43247-025-02149-9.
An Assessment of Potential Severe Droughts in the Colorado River Basin	2022-09-15	Salehabadi et al.	Salehabadi, Homa, David G. Tarboton, Bradley Udall, Kevin G. Wheeler, and John C. Schmidt. “An Assessment of Potential Severe Droughts in the Colorado River Basin.” JAWRA Journal of the American Water Resources Association, September 15, 2022, 1752-1688.13061. https://doi.org/10.1111/1752-1688.13061.	Much has been learned about Colorado River hydrology since the severe sustained drought study in 1995. We summarize our updated understanding of plausible future drought conditions by considering historical ﬂows, tree-ring reconstructions, and climate change. We focus on natural streamﬂow at Lees Ferry, the primary metric used to quantify the runoff in the Colorado River Basin. We identify drought periods using historical records and tree-ring reconstructed streamﬂow at Lees Ferry, which we then use to characterize potential future droughts. Resampling from past drought periods generates plausible future conditions to consider during planning. We produced three drought scenarios, each comprising 100 streamﬂow sequences to be used as input to systems operation and management models. We used analysis of the duration-severity and cumulative deﬁcit relative to the mean natural ﬂow to evaluate droughts and drought simulations and show that the current millennium drought that started in 2000 has an average ﬂow far less than the historical record. However, the ﬂows reconstructed from tree rings or future ﬂows projected from climate models indicate that even more severe droughts are possible. When used as input to the Colorado River Simulation System the drought scenarios developed indicate considerable periods when Lake Powell falls below its hydropower penstocks, indicating a need to rethink management and operation of these reservoirs during these critical conditions.
What will it take to stabilize the Colorado River?	2022-07-22	Wheeler et al.	Wheeler, Kevin G., Brad Udall, Jian Wang, Eric Kuhn, Homa Salehabadi, and John C. Schmidt. “What Will It Take to Stabilize the Colorado River?” Science 377, no. 6604 (July 22, 2022): 373–75. https://doi.org/10.1126/science.abo4452.	A continuation of the current 23-year-long drought will require difficult decisions to prevent further decline , The Colorado River supplies water to more than 40 million inhabitants in the southwestern United States and northwestern Mexico. A basin-wide water supply crisis is occurring because of decreased watershed runoff caused by a warming climate and legal and water management policies that allow systematic overuse. By the end of 2022, combined storage in Lake Powell and Lake Mead, the two largest reservoirs in the United States, will have declined from 95% full in 2000 to approximately 25% full. If this “Millennium Drought” persists, then stabilizing reservoir levels to avoid severe outcomes will require reducing water use to match diminished runoff. With a process underway to renegotiate interstate and international agreements on consumptive uses of the river, we describe a promising new management approach based on combined storage of both reservoirs, rather than just Lake Mead as currently used, to trigger consumptive use reductions to the Lower Basin and Mexico.
Managing Colorado River risk	2021-05-28	Fleck and Udall	Fleck, John, and Brad Udall. “Managing Colorado River Risk.” Science 372, no. 6545 (May 28, 2021): 885–885. https://doi.org/10.1126/science.abj5498.
Alternative Management Paradigms for the Future of the Colorado and Green Rivers	2021	Wheeler et al.	Wheeler, Kevin, Eric Kuhn, Lindsey Bruckerhoff, Brad Udall, Jian Wang, Lael Gilbert, Sara Goeking, et al. “Alternative Management Paradigms for the Future of the Colorado and Green Rivers.” Future of the Colorado River Project. Utah State University, Logan, UT: Center for Colorado River Studies, 2021.
The future hydrology of the Colorado River Basin	December 2020	Salehabadi et al.	Salehabadi, Homa, David Tarboton, Eric Kuhn, Brad Udall, Kevin Wheeler, David Rosenberg, Sara Goeking, and John C Schmidt. “The Future Hydrology of the Colorado River Basin.” White Paper No. 4. Future of the Colorado River Project. Center for Colorado River Studies: Utah State University, December 2020. https://www.fs.usda.gov/rm/pubs_journals/2020/rmrs_2020_salehabadi_h001.pdf.
Climate change and the aridification of North America	2020-06-02	Overpeck and Udall	Overpeck, Jonathan T., and Bradley Udall. “Climate Change and the Aridification of North America.” Proceedings of the National Academy of Sciences 117, no. 22 (June 2, 2020): 11856–58. https://doi.org/10.1073/pnas.2006323117.
On the causes of declining Colorado River streamflows	09/2018	Xiao et al.	Xiao, Mu, Bradley Udall, and Dennis P. Lettenmaier. “On the Causes of Declining Colorado River Streamflows.” Water Resources Research 54, no. 9 (2018): 6739–56. https://doi.org/10.1029/2018WR023153.
Fourth National Climate Assessment-Chapter 25: Southwest	2018	Gonzalez et al.	Gonzalez, Patrick, G. M. Garfin, D. D. Breshears, K. M. Brooks, H. E. Brown, E. H. Elias, A. Gunasekara, et al. “Fourth National Climate Assessment-Chapter 25: Southwest,” 2018. https://nca2018.globalchange.govhttps://nca2018.globalchange.gov/chapter/25.	This report is an authoritative assessment of the science of climate change, with a focus on the United States. It represents the second of two volumes of the Fourth National Climate Assessment, mandated by the Global Change Research Act of 1990.
The twenty-first century Colorado River hot drought and implications for the future	03/2017	Udall and Overpeck	Udall, Bradley, and Jonathan Overpeck. “The Twenty-First Century Colorado River Hot Drought and Implications for the Future.” Water Resources Research 53, no. 3 (2017): 2404–18. https://doi.org/10.1002/2016WR019638.	Between 2000 and 2014, annual Colorado River ﬂows averaged 19% below the 1906–1999 average, the worst 15-year drought on record. At least one-sixth to one-half (average at one-third) of this loss is due to unprecedented temperatures (0.98C above the 1906–1999 average), conﬁrming model-based analysis that continued warming will likely further reduce ﬂows. Whereas it is virtually certain that warming will continue with additional emissions of greenhouse gases to the atmosphere, there has been no observed trend toward greater precipitation in the Colorado Basin, nor are climate models in agreement that there should be a trend. Moreover, there is a signiﬁcant risk of decadal and multidecadal drought in the coming century, indicating that any increase in mean precipitation will likely be offset during periods of prolonged drought. Recently published estimates of Colorado River ﬂow sensitivity to temperature combined with a large number of recent climate model-based temperature projections indicate that continued business-as-usual warming will drive temperature-induced declines in river ﬂow, conservatively 220% by midcentury and 235% by end-century, with support for losses exceeding 230% at midcentury and 255% at end-century. Precipitation increases may moderate these declines somewhat, but to date no such increases are evident and there is no model agreement on future precipitation changes. These results, combined with the increasing likelihood of prolonged drought in the river basin, suggest that future climate change impacts on the Colorado River ﬂows will be much more serious than currently assumed, especially if substantial reductions in greenhouse gas emissions do not occur.
Understanding Uncertainties in Future Colorado River Streamflow	01/2014	Vano et al.	Vano, Julie A., Bradley Udall, Daniel R. Cayan, Jonathan T. Overpeck, Levi D. Brekke, Tapash Das, Holly C. Hartmann, et al. “Understanding Uncertainties in Future Colorado River Streamflow.” Bulletin of the American Meteorological Society 95, no. 1 (2014): 59–78. https://doi.org/10.1175/BAMS-D-12-00228.1.
Combined impacts of current and future dust deposition and regional warming on Colorado River Basin snow dynamics and hydrology	2013-11-07	Deems et al.	Deems, Jeffrey S., Thomas H. Painter, Joseph J. Barsugli, Jayne Belnap, and Bradley Udall. “Combined Impacts of Current and Future Dust Deposition and Regional Warming on Colorado River Basin Snow Dynamics and Hydrology.” Hydrology and Earth System Sciences 17, no. 11 (November 7, 2013): 4401–13. https://doi.org/10.5194/hess-17-4401-2013.
Response of Colorado River runoff to dust radiative forcing in snow	2010-10-05	Painter et al.	Painter, Thomas H., Jeffrey S. Deems, Jayne Belnap, Alan F. Hamlet, Christopher C. Landry, and Bradley Udall. “Response of Colorado River Runoff to Dust Radiative Forcing in Snow.” Proceedings of the National Academy of Sciences 107, no. 40 (October 5, 2010): 17125–30. https://doi.org/10.1073/pnas.0913139107.
Rethinking vulnerability on the Colorado River	03/2010	Kenney et al.	Kenney, Doug, Andrea Ray, Ben Harding, Roger Pulwarty, and Brad Udall. “Rethinking Vulnerability on the Colorado River.” Journal of Contemporary Water Research & Education 144, no. 1 (2010): 5–10. https://doi.org/10.1111/j.1936-704X.2010.00068.x.	On the Colorado River (as elsewhere), severe drought is useful for illuminating sources of water supply vulnerability, focusing attention on deficiencies in water allocation and management. A major drought study in the early 1990s, and experience with real drought a decade later, both have been useful in understanding vulnerability as a function of several factors working in consort with drought, including water allocation, reservoir operations, water demands, and climate change. Over this relatively short time-frame, vulnerability has shifted considerably, and will undoubtedly continue to change further in coming decades. Understanding how vulnerability is shifting is central to identifying future management pathways and reform options for the river.
Water supply risk on the Colorado River: Can management mitigate?	08/2009	Rajagopalan et al.	Rajagopalan, Balaji, Kenneth Nowak, James Prairie, Martin Hoerling, Benjamin Harding, Joseph Barsugli, Andrea Ray, and Bradley Udall. “Water Supply Risk on the Colorado River: Can Management Mitigate?” Water Resources Research 45, no. 8 (2009). https://doi.org/10.1029/2008WR007652.
Climate Change in Colorado: A Synthesis to Support Water Resources Management and Adaptation	2008	Ray et al.	Ray, Andrea J., Joseph J. Barsugli, K. B. Averyt, K. Wolter, Martin P. Hoerling, N. Doesken, B. Udall, and R. S. Webb. “Climate Change in Colorado: A Synthesis to Support Water Resources Management and Adaptation,” 2008. https://wwa.colorado.edu/publications/reports/WWA_ClimateChangeColoradoReport_2008.pdf.