The Colorado River Basin

U.S. Department of the Interior

U.S. Geological Survey

Fact Sheet 2010–3123

January 2011 Printed on recycled paper

The health of the Colorado River watershed

(fig. 1) is critical to the socioeconomic and

ecosystem well-being of the Southwestern United

States. Water in springs, streams, and rivers supports a range of aquatic and riparian ecosystems

that contain many endangered species. Terrestrial

habitats support a wide array of plants and wildlife. In

addition, this region is enjoyed by millions of people

annually for its recreational and esthetic opportunities. The Colorado River provides water for about

25 million people and is used to irrigate 2.5 million

acres of farmland. However, competition for this

water is expected to increase as human populations

dependent on this water are projected to increase to

38 million by 2020 (Pulwarty and others, 2005).

Climate change is expected to further

exacerbate water issues in this region. Drought in the

Southwest during 2000–04, caused by both reduced

precipitation and a series of the hottest years on

record, resulted in streamflows lower than during the

1930s Dust Bowl or the 1950s drought (Andreadis and

Lettenmaier, 2006). Increased temperatures alone are

a major factor in reducing surface-water flows in this

region. For instance, precipitation received during the

winter of 2005 was at the 100-year average. However,

low soil moisture and high January–July temperatures resulted in flows that were only 75 percent of

average (National Research Council, 2007). Climate

models predict future warmer temperatures and

reduced precipitation in the Upper Colorado River

Basin (UCRB), which would reduce water available to

humans and ecosystems.

The U.S. Geological Survey (USGS) and numerous partners have ongoing research activities assessing the magnitude

and effects of numerous climatic and human-induced changes affecting water availability and quality in the Colorado

River Basin. This fact sheet summarizes selected major research efforts (both USGS and others) to evaluate the effects

of climate and landscape change on water availability and water quality in the UCRB and describes some of the science

needed to support future management decisions.

Figure 1.  The Colorado River Basin with the Upper Basin outlined in red.

Effects of Climate Change and

Land Use on Water Resources

in the Upper Colorado River Basin

Background photograph by Jeff Foster, U.S. Geological Survey.
Background photograph by Dennis Smits, U.S. Geological Survey.

Climate Models Forecast Future Water Supply

Current climate models predict that by 2100, reductions in precipitation in the Southwestern United States, coupled with rises in 

temperatures as much as 5°F, and associated increases in evapotranspiration could result in changes in water runoff in the Colorado 

River Basin of up to 20 percent (table 1) (Milly and others, 2005; Christensen and others, 2007; Seager and others, 2007). Models 

predict that by 2070 the Colorado River Compact and the U.S. agreements with Mexico will be met only 60 percent of the time 

(McCabe and Wolock, 2007; National Research Council, 2007). By 2050, increasing temperatures alone are expected to increase 

evaporation such that average soil moisture conditions in the Southwest may be lower than the conditions experienced during any 

of the most severe droughts of this century, including the 1930s Dust Bowl and 

the droughts of 1953–1956 or 1999–2004 

(fig. 2). Increasing temperatures and 

reduced rainfall may also result in changes 

in vegetation cover. This, combined with 

other human disturbances related to land 

use and resource management, can affect 

the timing of snowmelt already altered by 

warming and may contribute to reduced 

total and late season water supplies in a 

substantial part of the American West. 

Related changes in water quantity and 

quality can create multiple natural-resource 

management and policy issues, affecting 

reservoir operations and water delivery for 

agriculture, communities, energy production, recreation, and wildlife. 

Study

Global

circulation models

(runs)

Spatial

scale Temperature Precipitation Year Runoff (flow) Riskestimate

Christensen and others (2004) 1 (3) VIC model grid 

(~8 mi) +3.1°F –6% 2040–69 –18% Yes

Milly (2005) replotted by P.C.D. Milly 12 (24)

(~100–300 mi)

CGM grids

— — 2041–60 –10% to –20%96% model agreement No

Hoerling and Eischeid (2007) 18 (42) NCDC Climate 

Division +5.0°F ~0% 2035–60 –45% No

Christensen and Lettenmaier (2007) 11 (22) VIC model grid 

(~8 mi)

+4.5°F

(+1.8 to +5.0)

–1%

(–21% to +13%) 2040–69 –6%(–40% to +18%) Yes

Seager and others (2007)* 19 (49) CGM grids

(~100–300 mi) — — 2050 –16%(–8% to –25%) No

McCabe and Wolock (2007) — USGS HUC8 units

(~25–65 mi) Assumed +3.6°F 0% — –17% Yes

Barnett and Pierce (2008)* — — — — 2057 Assumed 

–10% to –30% Yes

*

Two studies are not specifically for the Upper Colorado River Basin. Seager and others (2007) is for a larger area that only partially overlaps the Upper Basin. Barnett and Pierce 

(2008) assume Lees Ferry streamflow changes to drive their water balance of reservoir storage.

Table 1.  Projected changes in Colorado River Basin runoff or streamflow in the mid-21st century. (Adapted from Ray and others, 2009.)

Projected Future Flows in the Upper Colorado River Basin

Recent models have indicated that climate change could reduce Colorado River Basin flow anywhere from 5 to 45 percent by 

2050 (see table below). Given this wide range, an effort by scientists from the Bureau of Reclamation, the National Oceanic and 

Atmospheric Administration, USGS, and several universities to reconcile these diverse projections has shown:

1. Eighty-five percent of the runoff entering the Colorado River originates from the 15 percent of the basin at the highest elevations;

2. Models generating the largest reductions were not accurate; and

3. The most accurate models show the range of likely flows by 2050 are 5 to 20 percent less than current flows (Ray and 

others, 2009). 

Table 1 and figure 2 illustrate how assumptions and analysis design affect future projections and how uncertainty of climate and 

runoff projections can be constrained. These results have been presented to Colorado River water managers, and future workshops are 

planned. For further information, contact Bradley Udall at bradley.udall@colorado.edu.

Figure 2.  Modeled changes in annual mean precipitation (P) minus evaporation (E)

for the Southwestern United States, averaged over 19 models. Median values are in

red and the 25th and 75th percentiles (pink shading) of the P-E distribution among the

19 models are shown, as are the ensemble medians of P (blue line) and E (green line)

for 1900–2100.

0.1

0.05

0

−0.05

−0.1

−0.15

−0.2

1900 1920 1940 1960 1980 2000

YEAR

MILLIMETERS PER DAY

2020 2040 2060 2080

Filtered P−E Anom, Median of 19 models (red), 25th to 75th (pink); 50th P (blue), 50th E (green)
The Reconstructed Paleoclimatic Record—The Past Illuminates the Future

Paleoclimatic records show that the 

last 100 years have been unusually wet in 

the Upper Colorado River Basin. Reconstructions of past climatic conditions and 

associated Colorado River flows based on 

tree-ring records indicate the early 20th 

century was wetter than any time period 

back to A.D. 800, and that period was wetter than most of the previous 10,000 years 

(fig. 3) (R.S. Thompson, oral commun., 

2010). Droughts of greater intensity than 

any in the historical record occurred in the 

UCRB in the 11th, 14th, 15th, and 16th 

centuries and lasted as long as 24 years. 

In comparison, the longest 20th century 

drought lasted 14 years, and all droughts 

were less intense than those in previous 

centuries. There are other indicators that 

the past century has been far wetter than 

previous periods. Alpine lake levels in the 

Colorado mountains have been higher in 

the past millennium than any previous time 

in the past 5,000 to 12,000 years (Woodhouse and others, 2010). Paleobotanical 

evidence shows upper tree-line elevations 

ca. 9,000 to 5,000 years ago were at least 

80 meters higher than those of today. Many 

climate models indicate warmer and drier 

future conditions in this region. Thus, if the past is a guide, then sustained periods of drought may return to the Upper Colorado 

River Basin. The warmer and drier future predicted by regional climate models is likely to exacerbate the drought conditions implied 

by the paleoclimate reconstructions creating conditions not yet experienced in recorded history. For further information, contact 

Bob Thompson at rthompson@usgs.gov.

120

WET

110

100

90

80

DRY

400 600 800 1000 1200 1400 1600 1800 2000

Remnant wood

Medieval Warm Period Little Ice Age

Living trees

AGE, IN YEARS A.D.

Eagle, Colorado, tree-ring record 25-year moving averages of ring width

TREE-RING GROWTH AS PERCENTAGE OF 1901−1950 MEAN

Figure 3.  Climate reconstructions from tree rings show that the latter half of the 21st

century has been wetter than any similar time periods back to A.D. 800, given the high

amount and extended time of above-average precipitation (green) relative to the very

few and short drought periods (orange). Tree rings show much longer and severe

droughts from A.D. 800 to 1200 than any experienced since then.

Living trees

Photograph by Connie Woodhouse, used with permission.

Remnant wood

Photograph by Kurt Chowanski, used with permission.
Airborne Dust—Land-Use Management and Effects on Water Supply

Wind-driven dust production is increased by drought, disturbance of the soil surface, the invasion of exotic annual grasses, and fire. 

A synergistic effect is created when surface disturbance occurs on invaded landscapes during drought years, and large amounts of soil can 

be lost from an area as a result (Belnap and others, 2009). Soil-disturbing activities—energy exploration and development, grazing, and 

recreation—in the UCRB reduce plant and soil-crust cover that provides soil-surface protection. Increasing temperatures and decreasing 

precipitation also slow the recovery of soil and vegetation from land-use disturbance, further increasing the frequency and magnitude of 

wind erosion. 

Large dust storms have both local and regional effects on water resources. Windblown material is deposited in ephemeral washes, 

and this additional sediment degrades water quality when water flows. In the UCRB, these sediments are commonly heavily laden with 

salts and heavy metals (Bentley and others, 1978) such as selenium, degrading water quality and affecting wildlife downstream. Most 

importantly, much of the dust produced from low-elevation land can be deposited on the snowpack of nearby mountains (Painter and 

others, 2007). During spring warming, the dark-colored 

dust absorbs heat, which increases the rate at which the 

underlying snowpack melts. Models show up to 7 percent of the annual input to the Colorado River results 

from early snowmelt (Painter and others, 2010). Earlier 

than usual runoff is problematic for water managers 

and commonly reduces our ability to store water. Early 

snowmelt also leaves soils exposed longer to solar 

radiation, increasing evaporation from plants and soils 

and the potential for dust generation. Both wind- and 

water-borne sediment is likely to reduce the quality 

and quantity of water in the Colorado River watershed. 

Identifying the type, size, and source of dust allows land 

managers to better locate the landscapes that are susceptible to generating dust and adjust the timing, intensity, 

and location of soil-disturbing activities in these areas 

during seasons when the potential for dust production is high. For further information, contact Jayne 

Belnap at jayne_belnap@usgs.gov or Tom Painter 

at thomas.painter@jpl.nasa.gov.

Changes In the Timing of Snowmelt and Streamflow In the Upper Colorado River Basin

More than 80 percent of the runoff from the UCRB comes from the melting of high-elevation snow. The mountain snowpack 

serves as a large natural reservoir, releasing water for humans and wildlife throughout the West during the spring and summer. Since 

the late 1970s, the onset of snowmelt in this region has shifted 2 to 3 weeks earlier coincident with increasing spring temperatures and 

declining snowfall (Clow, 2010). Climate projections indicate that snowmelt timing will continue to advance in response to additional 

warming (Rauscher and others, 2008). Windblown dust loading on the mountain snowpack may exacerbate the problem (see photographs and following section). The observed trends in snowmelt timing have resulted in a similar shift in streamflow timing; these 

changes may require changes in reservoir management and water usage by cities and farms and may have important implications for 

fish and other aquatic biota that depend on maintenance of minimum streamflows during the fall and winter low-flow period. For further information, contact Dave Clow at dclow@usgs.gov or Tom Painter at thomas.painter@jpl.nasa.gov.
Forest Die-Off and Mountain Pine Beetle

Fish Futures and Changing Riparian Habitat in the Colorado River Basin

In addition to climate change, other factors may affect local and regional water supplies. At higher elevations, trees are succumbing to beetle kill and drought, with large areas of dead trees now present in Colorado, New Mexico, Arizona, and Utah. Although the 

mountain pine beetle (Dendroctonus ponderosae) is a native insect, several factors have contributed to its current epidemic population 

outbreak: increasing air temperatures and recent drought (possibly related to climatic change) and the presence of contiguous stands of 

mature, dense forest. Trees are now dead and dying throughout over 3 million acres of Colorado forests. This mortality could significantly decrease water quality and likely will affect snowmelt rates and runoff timing. USGS scientists are collaborating with several 

local and Federal partners on interdisciplinary research to characterize effects of this large-scale forest mortality on ecosystem structure 

and function, potential fire hazard, and water resources in this region. The quantity and timing of water supply is being monitored to 

detect changes related to forest die-off. Changes in water quality have already been detected. Although nitrate concentrations in streams 

flowing into and out of key drinking-water reservoirs in the headwaters of the Colorado River have remained stable or even declined, 

total phosphorus concentrations have increased in some streams by 30 to 60 percent since the beetle infestation began (Dave Clow, 

U.S. Geological Survey, oral commun., 2010). This may contribute to algal blooms that can cause anoxia and fishkills in the reservoirs. 

Results from these studies will help water-resource managers and water suppliers to understand, plan for, and adapt to changes in the 

quality of water available for consumptive use in the Upper Colorado River Basin and adjacent watersheds. For further information, 

contact Dave Clow at dclow@usgs.gov or Jenny Briggs at jsbriggs@usgs.gov.

Native fishes in the Colorado River and its tributaries 

evolved in a dynamic environment, with extreme swings in 

water flow and sediment loads. However, large dams have 

altered the timing, amount, and temperature of river flows. 

These changes, when combined with the introduction of nonnative reservoir and river fishes, have imperiled native fishes. 

Future projections for the Colorado River include reduced 

flows, warmer water, and greater human demands for this water. 

Although the effects of changing water temperatures on the 

interactions between native and nonnative fishes is not known, it 

is known that declining water availability will make the restoration of endangered fish habitat extremely challenging. 

Riparian areas in the Colorado River Basin are important 

transitions between the arid uplands and water bodies. Riparian areas provide diverse habitat for a large variety of plant and 

animal species, important linkage corridors for amphibians, birds, and mammals, and breeding areas for many species. Species like cottonwood depend on high spring flows for germination, and these conditions may not occur in the future, threatening these large gallery 

forests and the species associated with them. As river flows decrease and human demands increase, there may be an increasing need for 

surface-water and groundwater withdrawal. These withdrawals may dry up streams and springs, thus eliminating many riparian habitats 

and endangering the living things that depend on them. For further information, contact Jeffrey Kershner at jeffrey_kershner@usgs.gov.

Photograph by Michael McGrath, used with permission.

Colorado River Cutthroat Trout
Science in Support of Management Decisions

Science is critical for making informed natural resource management decisions. The U.S. Geological Survey and Federal and nonFederal partners are exploring ways to mitigate and adapt to future climate and landscape changes. Still, there are many critical research

and monitoring efforts needed to enhance this effort, including the following examples:

• Maintain and augment current monitoring networks, such as streamflow, water quality, snowmelt, groundwater, springs, vegetation,

air quality, aquatic ecosystems, and climate, to document how resources are changing. Consider establishing instrumented watersheds to better understand how hydrology, climate, land use, and vegetation interact to influence water quantity and quality.

• Document climatic and land-use histories to provide context in which to understand current trends.

• Monitor and measure dust at chronic and acute dust sources. Expand mapping of vulnerable soils and suggest ways to reduce

dust production.

• Develop better understanding of groundwater recharge and how to assess the effects of water withdrawals.

• Develop forecasting abilities for climate and water supplies across different temporal and spatial scales to evaluate the potential

consequences of alternative management scenarios.

• Develop integrated tools for evaluating watershed-scale ecosystem health.

• Document the effects of altered hydrologic cycles on aquatic and riparian resources, as stresses on these landscape components

increase in the future.

• Enhance communication between scientists and managers/policymakers.

References

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over the continental United States: Geophysical Research Letters, v. 33, 

p. L10403, doi:10.1029/2006GL025711.

Barnett, T.P., and Pierce D.W., 2008, When will Lake Mead go dry?: Water 

Resources Research, 44, W03201, doi:10.1029/2007WR006704.

Belnap, Jayne, Reynolds, R.L., and others, 2009, Sediment losses and gains 

across a gradient of livestock grazing and plant invasion in a cool, semi-arid 

grassland, Colorado Plateau, USA: Aeolian Research v. 1, p. 27–43.

Bentley, R.G., Jr., Eggleston, K.O., Price, D., Frandsen, E.R., and Dickerman, 

A.R., 1978, The effects of surface disturbance (primarily livestock use) on 

the salinity of public lands in the Upper Colorado River Basin—1977 Status 

Report: Denver, Colorado, U.S. Department of the Interior, Bureau of Land 

Management, Denver Service Center, Division of Standards and Technology, 

Watershed Staff.

Christensen, J.H., Hewitson, B., Busuioc, A., Chen, A., Gao, X., Held, I., Jones, 

R., Kolli, R.K., Kwon, W.T., Laprise, R., Magaña Rueda, V., Mearns, L., 

Menéndez, C.G., Räisänen, J., Rinke, A., Sarr, A., and Whetton, P., 2007, 

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Z., Marquis, M., Averyt, K.B., Tignor, M., and Miller, H.L., eds., Climate 

change 2007—The physical science basis: Contribution of Working Group I 

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Change, Cambridge, Cambridge University Press, p. 848–940.

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approach to assessment of climate change impacts on the hydrology and 

water resources of the Colorado River Basin: Hydrology and EarthSystem 

Sciences, 11, p. 1417–1434.

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Colorado—A response to recent warming: Journal of Climate, v. 23, no. 9, 

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supply shortages in the Colorado River basin: Geophysical Research Letters, 

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 For further information contact:

Jayne Belnap

U.S. Geological Survey

Moab, Utah

jayne_belnap@usgs.gov

Donald H. Campbell

U.S. Geological Survey

Denver, Colorado

dhcampbe@usgs.gov

National Research Council, Committee on the Scientific Bases of Colorado River Basin Water Management, 2007, Colorado River Basin Water 

Management—Evaluating and adjusting to hydroclimatic variability: Washington, D.C., National Academies Press, 242 p. 

Painter, T.H., Barrett, A.P., Landry, C.C., Neff, J.C., Cassidy, M.P., Lawrence, 

C.R., McBride, K.E., and Farmer, G.L., 2007, Impact of disturbed desert 

soils on duration of mountain snow cover: Geophysical Research Letters, 

v. 34, no. L12502, doi:10.1029/2007GL030284.

Painter, T.H., Deems, J.S., Belnap, J., Hamlet, A.F., Landry, C.C., and Udall, 

B.H., 2010, Response of Colorado River runoff to dust radiative forcing in 

snow: Proceedings of the National Academy of Sciences (PNAS), accessed 

Oct. 19, 2010, at http://www.pnas.org/content/107/40/17125.

Pulwarty, R., Jacobs, K., and Dole, R., 2005, The hardest working river—

Drought and critical water problems on the Colorado, in Wilhite, D., ed., 

Drought and water crises—Science, technology and management: New York, 

Taylor and Francis Press, p. 249–285.

Rauscher, S.A., Pal, J.S., Diffenbaugh, N.S., and Benedetti, M.M., 2008, Future 

changes in snowmelt-driven runoff timing over the western US: Geophysical 

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Ray, A.J., Barsugli, J.J., Averyt, K.B., Wolter, K., Hoerling, M., Doesken, N., 

Udall, B., and Webb, R.S., 2009, Climate change in Colorado—A synthesis 

to support water resources management and adaptation: Colorado Water Conservation Board, State of Colorado, at http://cwcb.state.co.us/

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Seager, R., Ting, M., Held, I., Kushnir, Y., Lu, J., Vecchi, G., Huang, H., Harnik, 

N., Leetmaa, A., Lau, N., Li, C., Velez, J., and Naik, N., 2007, Model predictions of an imminent transition to a more arid climate in Southwestern North 

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E.R., 2010, A 1,200-year perspective of 21st century drought in southwestern 

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