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From the report Colorado River Insights, 2025: Dancing With Deadpool (Jonathan Overpeck and Bradley Udall):

• Jonathan Overpeck is a climate scientist and Dean of the School for Environment and Sustainability at the University of Michigan; prior to moving to Michigan, he lived and worked in Colorado and Arizona for over 25 years.
• Bradley Udall is a Senior Water and Climate Research Scientist/Scholar, Colorado Water Center, Colorado State University.

Basin status update

Back in 2017, we published a peer-reviewed research paper (Udall and Overpeck, 2017) asserting that climate warming was a principal cause of the then eighteen-year Colorado River drought, a drought that had already seen a 17% reduction in natural flows of the river. We expressed confidence that warming would continue to eat away at these flows until the warming (due to greenhouse gas emissions, high confidence) ceased and suggested that increases in precipitation would likely not be able to compensate for the long-term impact of rising temperatures. We used the term “Hot Drought” to distinguish this period from the “Dry Droughts in the 20th century. This important concept continues to be researched and confirmed (King et al, 2024, Zhuang et al, 2024). Now, eight years later, as the warming has continued unabated and may be accelerating (Hansen et al, 2025, Ripple et al., 2025), it has become clearer than ever that precipitation declines have also played an important role in causing the worst drought in at least 1200 years (Williams et al., 2022). More troubling, however, is new evidence that human caused climate change is not only driving a steady increase in temperature but is also the main culprit behind the precipitation declines as well.

This is clearly bad news, but there is a silver-lining. But first, let’s review where we are with respect to the unprecedented 21st century Colorado River drought, and the new evidence suggesting the situation is worse than we first thought.

Each year one of us updates a figure³ that was first published in our 2017 paper showing the status of the Colorado River drought and its climate drivers. We’ve included this figure here, updated through the September 30th end of the 2024-25 water year (Figure 1). The combined volume of water stored in Lakes Mead and Powell has continued its decline to less than 15 maf (million acre-feet), the 26-year average naturalized flow of the Colorado River at Lees Ferry is now 12.2 maf, well below the 16.5 maf mainstem apportionments assigned to the seven Colorado River Basin states and Mexico. Critically, the 6 years since 2020 have averaged 10.8 maf/year, the same as the then-unprecedented low flows during 2000-05 at the start of this record-setting drought.

Matching the long slow decline in naturalized flows over the last century has been a similar long slow decline in precipitation in the Upper Basin of the Colorado (Figure 1, Panel C). Superimposed on this long trend are two notable drought periods with lower-than-average precipitation: one in the 1950’s-60’s and now the on-going current drought, at 26-years and counting, a multidecadal “megadrought” and the longest drought in the Colorado River Basin instrumental record. Mirroring the century-long declines in precipitation and naturalized flows is a long-term warming trend that started to accelerate in the 1970’s and that is clearly linked to on-going global warming (Williams et al., 2020, Masson-Delmotte et al., 2021). Whereas the former drought of record, in the 1950’s and 60’s, was defined almost entirely by precipitation deficit (Figure 1, left gray shaded area), the current megadrought is being driven by a precipitation deficit compounded by relentless warming (Figure 1, right gray shaded area).

The impact of a warming climate

As we highlighted in earlier peer-reviewed papers (e.g., Vano et al., 2014, Udall and Overpeck, 2017), warming exacerbates drought in multiple ways. A warming atmosphere can hold progressively more water, and thus as the atmosphere warms it can evaporate more water. At the same time, a warmer atmosphere can cause soils and vegetation to lose more water to the atmosphere via evapotranspiration, especially as the warming atmosphere also causes the growing season in the Upper Basin of the Colorado to become longer (Das et al., 2011; Udall and Overpeck, 2017). Hot, dry springs in the basin bring on early melt and green-up (Hogan and Lundquist, 2024, Lin et al., 2022). Drier soils and vegetation thus mean less water that can eventually end up in the river, and incidentally also explains why the West I experiencing more wildfire (Abatzoglou and Williams, 2016). Atmospheric warming also leads to snow loss, a shorter snow-cover season, and an associated loss of solar radiation reflectivity – this drives further warming and yet more evapotranspiration (Milly and Dunne, 2020; Ban et al., 2023).

Large changes in groundwater supplies in both the Upper and Lower Colorado River Basins have been noted from soil moisture to deeper layers since 2002 (Abdelmohsen et al., 2025, Chandanpurkar et al., 2025). It is becoming increasingly clear that dry summer soils can persist into the fall and winter soaking up snowmelt the following spring thereby reducing runoff (Das et al., 2011, Lapides et al, 2022).

Precipitation declining

Estimates vary, but it appears that up to half of the observed roughly 20% reduction in Colorado flows are likely related to the steadily warming temperatures of the Colorado River headwaters region (Udall and Overpeck, 2017; Xiao et al., 2018; Milly and Dunne, 2020, Bass et al, 2023). Moreover, since 2017 it has become increasingly clear that the other major cause of the flow reductions is a sustained decrease in precipitation (Figure 1, Panel C). Until recently, the big question is whether the observed 7% post-1999 decrease in precipitation relative to the 20th century average was due primarily to natural multidecadal climate variability or human-caused climate change.  We now have good reasons to suspect the latter, and this translates to mostly bad news.

Megadrought country

It is now more clear than ever that the southwest United States, including the headwater regions of the Colorado River, is megadrought country. Tree-ring and other paleoclimatic sources reveal that multiple droughts lasting two or more decades took place over the last 2000 years (Meko et al, 2007; Gangopadhyay et al., 2022), and a good case has now been made for the current drought being among the most severe in at least 1200 years in large part because of the unprecedented amplifying effect of warming temperatures during the current sustained period of reduced precipitation (Williams et al., 2020; 2022).

However, there is another important lesson to be gleaned from the rich paleoclimatic record of pre-20th Century droughts and megadroughts. Given that global temperatures were likely significantly cooler prior to the last 50 years then they are now (PAGES 2k Consortium, 2019), it follows that themany long Upper Colorado Basin droughts that took place over the last 2000 years preceding the current drought were likely due much more to precipitation deficits alone. This means that we have good evidence that precipitation deficits exceeding those of the current on-going drought in both magnitude and duration are not rare, and that the current drought could see not just warmer temperatures in the future (a sure bet), but also even larger and longer precipitation deficits. It is thus critical that we consider what is presently causing the precipitation decline in the headwaters region of the Colorado River, and from that get a better sense of what’s most likely ahead. And for motivation, since we wrote our 2017 paper, new evidence has emerged that drought-dominated periods – likely driven mostly by precipitation declines for the reason noted above – as long as 80 years have occurred in the last 2000 years in the Upper Basin of the Colorado River (Gangopadhyay et al., 2022).

The cause of precipitation decline

Could we be in for an even longer period of reduced precipitation than the last quarter. century in the years to decades ahead? The answer depends on knowing the cause of the on-going precipitation decline, and there are two primary possibilities. The first is natural climate variability in the climate system, which can cause periods of lower precipitation to oscillate irregularly with periods of higher precipitation. Thus, if the recent period of low precipitation is due to natural climate variability, there could be periods of greater precipitation returning to the Colorado headwaters, although these wet periods would be increasingly unlikely to offset the drying impact of the steadily increasing temperatures. The second potential cause of on-going precipitation deficit is an anthropogenically-forced trend in precipitation decline due to increasing human emissions of greenhouse gases and reductions in Asian, mostly Chinese, aerosols to the atmosphere.5 Such an anthropogenic trend would likely portend continued low precipitation into the future, in synch with continued warming.

One well-known source of natural variability in precipitation in the Colorado River Basin is decadal and longer variation in the sea-surface temperature patterns of the North and tropical Pacific Ocean, giving rise to what is called the Pacific Decadal Oscillation (PDO). A peer-reviewed research paper just published (Klavans et al., 2025) reviews the scientific literature and notes that decadal and longer variability in the PDO has long been thought to have arisen from atmosphere-ocean interactions internal to the natural climate system and has in turn caused decadal and longer precipitation variability downstream over western North America. The PDO is strongly correlated with La Nina, and both are known to be associated with a dry Southwest US (Seager and Ting, 2017; Lehner et al., 2018; Hoerling et al., 2023, Seager et al., 2023). Klavans et al., 2025 also presents convincing new evidence that anthropogenic forcing in the form of human emissions of greenhouse gases and reductions in atmospheric aerosols is now the primary driver of the same elevated sea-surface temperatures and this forcing is thus the primary cause behind the precipitation decline that has been observed since the start of the on-going Colorado River megadrought. In other words, human-driven climate change has caused the PDO oscillation to lock into its negative dry phase and this situation is likely to persist into the future.

A second new paper (Todd et al., 2025) highlights that higher Northern Hemisphere temperatures from about 11,000 to 6,000 years ago, in this case due to well-understood changes in the Earth’s orbit, caused a negative PDO-like Pacific warming that in turn forced western U.S. precipitation to lock into a multi-millennia-long dry phase. This new research thus provides yet more confidence that the odds will favor lowered precipitation in the Colorado River headwaters for as long as human-caused warming persists. Both new research papers (Todd et al., 2025; Klavans et al., 2025) also note that state-of-the-art climate models underestimate the role of human-caused climate change in driving persistent drought in the region containing the headwaters of the Colorado River. Natural decadal and longer climate variability clearly caused the many droughts and megadroughts of the last 2000 years, but looking ahead today, it appears that human-caused climate change is likely to exert a stronger influence, and this will mean a higher likelihood of continued lower precipitation in the headwaters of the Colorado River into the future.

Conclusion: bad news, good news

To sum it up, since 2017 we now know quite a bit more about how climate change is altering the flows of the Colorado River. Whereas eight years ago we were able to confidently anticipate that human-caused atmospheric warming alone would continue to reduce flows in the river, we now have a better, though still emerging, understanding of how human emissions of greenhouse gases are likely to also cause a continued reduction in precipitation in the headwaters of the Colorado River. Whereas we have known since 2017 that additional future climate warming will cause continued and even larger flow reductions, two new carefully crafted studies strongly suggest we are in for extended dry periods in the Colorado headwaters in the decades ahead.

As we hinted earlier, is important to recognize that the news is not all bad, and there is indeed a silver-lining to our improved understanding of why the natural flows of the Colorado are declining, and what this means for the future. We can say with confidence that human-caused emissions of greenhouse gases are having an increasingly negative impact on the flows of the Colorado River, a river that serves over forty million people and region that has an annual economy in excess of $1.4 trillion (James et al., 2014). This climate change impact will continue to worsen, but because humans cause it, humans can halt it. This is good to know as we work to reduce the greenhouse gas emissions to the atmosphere that are causing the climate change. The Colorado River will benefit. 

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Footnotes

³ https://coloradoriverscience.org/Current_conditions#The_Colorado_River_.274-panel_plot.27

⁴ NOAA’s nClimGrid dataset indicates that over the Upper Colorado River Basin there has been a 7% annual precipitation reduction during 2000-26 compared to 1897-1999. This reduction is not evenly spread over the seasons, however; reductions in the fall (SON), winter (DJF), spring (MAM) and summer (JJA) are 3%, 0%, 11% and 12%, respectively. Fall and winter precipitation for snowpack has thus been close to normal while spring and summer has been much reduced.

⁵ Sulfate aerosols are emitted in large quantities when sulfur in fossil fuels is burned. These shiny particles can end up high in the atmosphere where they reduce anthropogenic warming by reflecting sunlight. But near the surface their sulfur-based precursors cause serious human health problems and thus many countries in the last few decades have tried and succeeded in reducing these emissions. China, notably, has made great strides in reducing these emissions but the unfortunate side effect is increased warming, especially in the Pacific Ocean downwind. It is believed that this aerosol cleanup (also underway in ocean shipping) is causing at least some of the accelerated global heating now underway including the additional heating in the northern Pacific contributing to precipitation reductions in the Southwest US.

Click the link to read the briefing on the Western Water Assessment website:

December 8, 2025 – CO, UT, WY

A hot and dry November left the Intermountain West with much below average snowpack conditions. November temperatures were four degrees above average region-wide and much of Utah and Wyoming baked under mean temperatures that were six to ten degrees above average. High temperatures coupled with mostly below normal precipitation caused low snow water equivalent (SWE) and worsening drought conditions.

November precipitation was much below average for much of the region, especially in Wyoming, northern Colorado and northern Utah, which received less than half of normal precipitation. Much above average November precipitation was observed in southern Utah and eastern Colorado. Record dry Novembers were observed at thirteen locations in Wyoming, ten locations in Colorado and five locations in Utah. Despite dry November conditions, regional water year precipitation is near to above average except for eastern Colorado and southeastern Wyoming.

November was an extremely warm month, especially in western Wyoming, where monthly temperatures were more than eight degrees above average. The entire region observed November temperatures that were at least four degrees above average, with all of Utah, nearly all of Wyoming and western Colorado experiencing temperatures that exceeded six degrees above average. Record warm October conditions were observed in western Colorado, southwestern Wyoming and throughout Utah.

Record low SWE conditions exist at many locations in Colorado, Utah and Wyoming. A hot and dry November left most regional river basins with SWE conditions at less than 50% of average, with the least snow in the Six Creeks near Salt Lake City, where December 1st SWE is 22% of median. Slightly better SWE conditions exist in southern Colorado and southern Utah.

Regional drought coverage expanded slightly during November, increasing from 51% five weeks ago to 54% on December 2. Eastern Colorado and eastern Wyoming remain drought-free, but drought emerged along the northern Front Range and adjacent plains. Coverage of drought in Utah dropped below 100% for the first time in five months. Utah and Colorado were last free from drought six years ago, while the current drought in Wyoming began five years ago.

A NOAA La Niña Advisory is still in effect as eastern Pacific Ocean temperatures are below average. Weak La Niña conditions are expected to transition (60% probability) to neutral conditions by early 2026. The NOAA December Precipitation Outlook suggests above average precipitation for most of Wyoming. For the winter months (Dec-Feb), there is an increased probability for above average temperatures in Utah and southwestern Colorado. In Wyoming, there is an increased probability for above average precipitation and below average temperatures.

Record high temperatures drive record low snowpack. On December 1, record low SWE conditions were present at 52 regional Snotel sites in northern Colorado, northern Utah, and across Wyoming. Despite very low snowpack conditions, water year precipitation is above average for the region, except in northern Colorado. During early October, daily precipitation records were set in Utah and Colorado, including widespread flooding in southwest Colorado. Due to the tropical origin of those storms, nearly all precipitation fell as rain. Contrasting precipitation, water year temperatures are much above average with record high temperatures observed in parts of western Colorado, eastern Utah, and southwestern Wyoming. Consequently, the current snow drought is primarily the result of high temperatures rather than low precipitation. While October precipitation generally fell as rain in regional mountains, above average precipitation has increased soil moisture, which could help to bolster the efficiency of runoff in 2026.

Click the link to read the article on the NOAA website:

November 20, 2025

Key Points

• Start of Water Year 2026: Leading up to the start of Water Year (WY) 2026, drought conditions improved across the eastern Intermountain West, but drought expanded and intensified across western areas of the region. Storage for Lake Powell and Lake Mead reached a 30-year low for the date as of October 25, 2025.
• Water Year 2025: Precipitation was lower than average in western portions of the region, and greater than average in eastern parts of Colorado, New Mexico, and Wyoming. Much of the Intermountain West experienced warmer-than-average temperatures.
• Water Year 2025 Impacts: Hot and dry conditions led to large fires in several states. Lack of precipitation, early snowmelt, and warm spring temperatures harmed crop production and forage in many areas.
• La Niña Winter Ahead: La Niña conditions are present and favored to continue into early winter. La Niña typically brings warmer and drier winter conditions to the southern region of the Intermountain West. A transition to El Niño-Southern Oscillation (ENSO) neutral is favored for the January-March 2026 time frame. Neutral conditions mean neither El Niño or La Niña are influencing weather patterns. 

This update is based on data available as of Thursday, November 20, at 7 a.m. MT. We acknowledge that conditions are evolving.

Conditions at the Start of Water Year 2026 

• The start of the new water year (beginning October 1, 2025) brought intense rainstorms and flooding in parts of Utah, Arizona, New Mexico, and Colorado. However, due to warmer-than-average temperatures, combined with lower-than-average precipitation across Water Year 2025, much of the region still remains in drought, according to the U.S. Drought Monitor.
• At the start of Water Year 2026, drought conditions were split across the Continental Divide, with no drought in much of the eastern extent of the Intermountain West region. Over Water Year 2025, drought conditions persisted or intensified across western portions of Colorado, Wyoming, and New Mexico, as well as statewide across Arizona and Utah.
• Flaming Gorge Reservoir started Water Year 2026 at near-average storage levels, but many other reservoirs remained below average, including Lake Mead, Lake Powell, and Elephant Butte Reservoir. Greater-than-average runoff is needed to increase reservoir levels next spring.
• Moving into winter, soil moisture levels are better than they were in November 2024, with root zone soil moisture in headwater basins for the Upper Colorado River and the Rio Grande River experiencing a mix of wetter-than-average conditions at some locations and drier than-average conditions at others, according to both SPoRT-LIS modeled data and SNOTEL station data.
• Storage is below average for most Bureau of Reclamation–managed reservoirs in the headwaters of the Upper Colorado River Basin. As of November 18, 2025, Lake Powell is at 44% of typical storage, the lowest observed level for this date in the last 30 years.
• Storage is also below average for Elephant Butte Reservoir in the Rio Grande Basin, at 11% of average as of November 18, 2025.
• With La Niña conditions anticipated to persist from December to February, snowpack is more likely to be lower than average during these months. However, all La Niñas differ, and there is uncertainty around how this season will play out. La Niña conditions are expected to weaken into El Niño-Southern Oscillation (ENSO) neutral conditions from January to March 2026.

Water Year 2025 Brings a Mix of Drought Degradation and Recovery 

November 2025 Reservoir Storage Levels

Intermountain West Water Year 2025 Summary

• Water Year 2025 (October 1, 2024–September 30, 2025) brought varied drought conditions to the Intermountain West. Drought largely worsened west of the Continental Divide and improved to the east of the Continental Divide.
• Drought intensified and spread in Utah, Arizona, and western portions of Colorado, Wyoming, and New Mexico. Over the summer, portions of western Colorado and the southern border of Arizona and New Mexico reached Exceptional Drought (D4), according to the U.S. Drought Monitor.
• Above-average temperatures (+ 1-3 ºF) were widespread across the region in Water Year 2025, with some isolated areas being even hotter.
• Water year precipitation for the region was variable, with a wet-dry split along the Continental Divide. The Southwest Monsoon season was slow to start this year, but precipitation ramped up at the end of August for Colorado, Arizona, and New Mexico. Utah had a weaker than usual summer rain season, and Salt Lake City experienced its fourth driest summer on record.
  • Utah: Total water year precipitation was below average across the entire state in 2025. The driest areas were in the south-central region of the state, and in Juab and Tooele Counties in Western Utah. Water Year 2025 was among the top five driest years on record for many portions of the state.
  • Arizona: Arizona received lower-than-average precipitation. Stations in some southeastern counties measured total water year precipitation among the lowest 10% on record, with some counties recording their 5th driest water year on record. August 2025 was the 16th driest August on record for the state. Yuma County was the only area with above-average precipitation, with the 9th wettest August on record for the county.
  • Colorado: Precipitation conditions were split between western and eastern Colorado. The western side of the state saw total water year precipitation between 50-90% of average. The eastern side of the state was unusually wet. Parts of Lincoln and Kit Carson Counties received over 130% of average precipitation.
  • New Mexico: Water year precipitation followed a diagonal split across the state. Temperatures were warmer than average for two-thirds of the state, and near average in counties to the northeast. The western and southern areas were drier than average (50-80% of average), and the eastern half of the state was wetter than average (100-150%). Hidalgo, Grant, and Catron Counties experienced the driest water year conditions in the state. Meanwhile, multiple counties on the eastern side of the state received 130-150% of average precipitation.
  • Wyoming: Total water year precipitation varied across Wyoming, ranging from 50-70% of average in parts of Sweetwater County to 120-130% of average in Converse County. Much of the state received 80-100% of average precipitation.
• April 1, 2025 snow water equivalent (SWE) was 81-96% of average for many headwater basins in the Upper Colorado, but runoff efficiency was low and yielded below-average streamflows in many reaches. The Colorado Climate Center attributed low runoff efficiency to early snowmelt and below-average spring snowfall. April 1, 2025 snowpack was much lower than average for the headwaters of the Rio Grande basin, located in southern Colorado, with SWE at ~56% of average for the basin.
• Dry conditions and high evaporative demand led to several large fires in the Intermountain West during the 2025 fire season, including the 145,000+-acre Dragon Bravo Fire in Arizona and 137,758-acre Lee Fire in Colorado (5th largest fire in Colorado history). 

Near- to Below-Average Precipitation West of the Continental Divide

Water Year 2025 Impacts

• High evaporative demand, warmer-than-usual temperatures, lower-than-usual precipitation, and dry soils contributed to dry fuel conditions and large fires across many parts of the Intermountain West. Across the region, earlier snowmelt and warm temperatures led to longer-than-usual fire seasons.
• Wildfire impacts across the Intermountain West varied by state during Water Year 2025. Arizona and Colorado experienced record-breaking fires, including the 145,000+ acre Dragon Bravo Fire in Grand Canyon National Park and 137,000 acre Lee Fire–Colorado’s 5th largest wildfire on record.  Meanwhile in Wyoming, the number of wildfire incidents increased, but acres burned decreased compared to Water Year 2024.
• By April 2025, conditions were so dry in Utah that the governor declared a drought emergency.
• Dry conditions, early snowmelt, and warm spring temperatures negatively impacted crop production in portions of all states across the Intermountain West. Poor forage conditions likewise harmed grazing in many areas, leading to curtailed grazing seasons or herd reductions. 

La Niña Outlook

• As of November 17, 2025, La Niña conditions are present and expected to continue through December to February, with a transition to El Niño Southern Oscillation–neutral conditions likely from January to March.
• Every La Niña is different. For the Southwestern U.S., La Niña is typically associated with a greater statistical likelihood of warmer, drier conditions during winter months.
• Other variables also influence winter precipitation, and not all La Niñas are associated with below-average winter precipitation in the Intermountain West.

A Weak La Niña Is Here, ENSO-Neutral Forecast Early Next Year

Additional Resources by State

• More local information is available from the following resources:
  • Your state climatologist
  • Your state page on Drought.gov:
    • Arizona
    • Colorado
    • New Mexico
    • Utah
    • Wyoming
  • National Weather Service Drought Information Statements:
    • November 7, 2025: Riverton, Wyoming Weather Forecast Office
    • November 4, 2025: Salt Lake City, Utah Weather Forecast Office
    • November 3, 2025: El Paso, Texas/Santa Teresa, New Mexico Weather Forecast Office
  • Western Water Assessment 2025 Water Year Summary
• More state information is available from the following resources:
  • Arizona: Interactive Drought Dashboard; State Climate Office
  • California: California Water Watch; California Department of Water Resources – Drought; California State Climatologist
  • Colorado: Water Conditions Monitoring Committee; Colorado Climate Center Drought Dashboard
  • Nevada: Living with Drought in Nevada; Nevada Division of Water Resources – Drought; State Climate Office
  • New Mexico: Office of the State Engineer, Drought page; New Mexico Climate Center
  • Utah: Department of Natural Resources, Drought page; Utah Climate Center
• To report or view local drought impact information:
  • Condition Monitoring Observer Reports (CMOR)
  • CoCoRaHS Condition Monitoring Reports

Elise Osenga
University of Colorado Boulder/Cooperative Institute for Research in Environmental Sciences (CIRES), NOAA/National Integrated Drought Information System (NIDIS)

Meredith Muth
NOAA National Integrated Drought Information System (NIDIS)

Erinanne Saffell
Arizona State Climate Office, Arizona State University

Dave Simeral
Desert Research Institute, Western Regional Climate Center

Jon Meyer
Utah Climate Center, Utah State University

Paul Miller
Colorado River Basin Forecast Center, National Weather Service

Special Thanks

This Drought Status Update was issued in partnership between the National Oceanic and Atmospheric Administration (NOAA)/National Integrated Drought Information System (NIDIS) and partners across the Intermountain West. NIDIS is an interagency program within the Climate Program Office, which is part of NOAA’s Office of Oceanic and Atmospheric Research.