Colorado River water supply

September 11, 2012, 2:20 pm
Content Cover Image

This curriculum module will look at the Colorado River water supply, climate issues and water extraction issues. We will study the data, the possible consequences to various user groups, and suggest solutions to adapt to and mitigate these changes.


Students will see how a changed climate can impact urban development, food security, regional economies, international relations, as well as the natural environment.

Students will be able to see how adaptation strategies and different from mitigation strategies and how these strategies can help minimize the impacts and make the Southwest region more sustainable.

Part One

Figure 1. NASA MODIS image of the Colorado River watershed.  Source: NASA

The first part of the assignment is to become acquainted with the Colorado River watershed as shown in this image. The source of the water is in the snowpack of regional mountain ranges (mostly the Rockies). It then flows southwest through the red desert of Glen Canyon National Park on through the Grand Canyon in Arizona, forming Lake Mead on the middle left side of the image, down through the agricultural lands on the California, Arizona and Mexico border. Look at where the water is coming from and the vast deserts it must travel through before reaching its destination in the Gulf of California. Who is using the water and for what purpose? 

As introduction to this module, you must first answer that question before continuing. Do some research and cite your sources. Give a brief explanation where the water is coming from and where it is going (most will be diverted without actually reaching the ocean). How will climate change impact your answer? We have also provided a graph and data set below that shows the percent of average snowpack found in Colorado that feeds into the Colorado River. Look at the data and answer the following questions.

Figure 2. Percent of  average snowpack found in Colorado that feeds   into the Colorado River



Table 1. Monthly percentages of average snowpack in Colorado for the Colorado River watershed for years 1968-2009.

  January February March April May June
1968   93 102 92 115  
1969   131 106 102 76  
1970   148 131 130 165  
1971   135 129 125 125  
1972   121 110 98 95  
1973   113 88 92 134  
1974   125 112 110 106  
1975   106 106 117 125  
1976   92 97 95 87  
1977   38 40 54 38  
1978   145 131 133 126  
1979   132 117 127 132  
1980   126 139 139 144  
1981   40 42 57 29  
1982   145 122 121 128  
1983   89 90 123 142  
1984   160 139 141 169  
1985 131 108 101 101 104  
1986   110 127 108 124 142
1987 80 73 70 73 43 20
1988 77 96 97 93 87 69
1989 91 85 96 83 59 39
1990 69 71 71 77 73 61
1991 76 75 71 89 108 62
1992 97 81 78 88 65 15
1993 105 102 126 124 151 145
1994 92 84 91 88 85 29
1995 84 81 98 103 132 321
1996 100 131 139 131 140 98
1997 160 161 140 118 142 146
1998 81 92 94 89 99 50
1999 65 89 89 75 91 99
2000 51 79 94 97 84 10
2001 95 82 85 86 79 18
2002 72 70 68 63 27 0
2003 93 82 93 101 105 47
2004 91 85 83 64 55 23
2005 96 102 98 98 88 73
2006 133 128 115 110 78 38
2007 102 91 95 81 71 34
2008 105 122 128 123 120 146
2009 127 123 115 104 99 31



  Figure 3. Colorado River Basin
  1. What are the units on the graph?

  2. When was the maximum amount of snowpack? When was the minimum amount of snow pack?

  3. Do these max/mins validate or disprove that climate change is occurring? Are max/mins an example of a region’s climate or weather? Explain.

  4. Pick a month (not January or June since they do not have complete data sets) and find the average from 1968 to 1988 and then find the average for 1989 to 2009. When did we get more snow and when did we get less snow?

  5. Is this data set long enough to establish whether climate change is occurring? Explain your answer. If there is less snowpack in the Colorado Rockies, what do you think that will mean for the amount of water available to the watershed?

  6. What will happen to the level of Lake Mead?

Click here to download Part One as a PDF

Part Two

From your results, you can see that a decrease in snowpack in the Colorado Rockies means less water in the river system.

The Colorado has over a dozen different dams that help to regulate and store the flow of water, but the law of the river dictates how much each dam must release to users downstream.

Less water in the system means less water coming into the reservoirs despite the fact that there are mandates on how much must be released. The result is lower water levels.

Less snow in Colorado means drops in lake levels.

Figure 4. Hoover Dam acts as the drain plug in the tub allowing the reservoir to fill up. Water is released to California and Arizona for their water use and production of hydro-electricity.

Figure 5. Lake Mead is the main indicator for the whole system. As the reservoir for the Lower Basin, its levels dictate how much needs to be released from the Upper Basin. Notice how Saddle Island and Black Island are no longer islands. You can also see that the notorious “bath tub ring” is now apparent in the satellite image of 2003, but not visible in the 2000 image. (Source)

Fugure 6.These images show a different region of Lake Mead during the same time periods as above. By looking at the reflectance of different wavelengths along the electromagnetic spectrum, we can see change in the landscape easier. In this image, NASA is using the near infrared part of the spectrum to make this image. Green vegetation shows up as bright red. You can see where the lake has receded leaving fertile, wet sediments that have been quickly colonized by plant communities. (Source)

Figure 7. Here is an overlap of the drop in Lake Powell’s level with a corresponding graph showing water storage. You can see that with less water coming in, but the demand for water staying high, the lake levels drop dramatically over a few short years.


caption Colorado River Basin

Seeing that the water stored for our use is dropping, we need to next look at how that water is being used.

The Colorado watershed covers 7 states and all seven are allocated a share of the water through the 1922 compact. The upper and lower basins get equal shares of the water, 7.5 MAFY each. Due to the decreased amount of water available a temporary agreement was reached in 2007. This 2007 interim drought agreement has it limited to 7.05 MAFY per basin until 2026. This assumes that the drought is a temporary condition or that a new agreement can be reached for the allocation of the water if this is in fact a new drier climate the region is now experiencing. The boundary between the basins is at Lee Ferry just below Glen Canyon Dam.

Table 2. shows each state’s allocations. Each state’s share of water reflects their state of development in 1922 when the original compact was negotiated.

Notice that Nevada gets a mere fraction of the water. All of Nevada’s allocation goes to the Las Vegas Valley for the municipal water supply. California gets the largest allocation for their agriculture and city centers and has been using over their allocated share (5 MAFY). Federal authorities have told California to come up with alternative sources to supplement their water supply to bring them back in compliance. Native American tribes are eligible for up to 1 MAFY but not all have claimed them, so others use their allotment.

The Mexico allocation is part of an international treaty, so they do get their portion of the water; however, the water quality is degraded by the time it reaches the end of the river.

Table 2. Water Allocation from the Colorado River  
Allocation Million Acre Feet Per Year (MAFY)
Upper Basin 7.5
Colorado   3.9  
Utah   1.7  
Wyoming   1.0  
New Mexico   0.85  
Lower Basin 7.5
Arizona   2.85  
California   4.4  
Nevada   0.3  
Additional Allocations  
Mexico   1.5  
Total 16.6


Figure 8. California's Imperial  Valley and the Coachella Valley. (Source)

One of the primary uses of the Colorado River in the arid west is for agriculture. 63% of water used in Upper Basin is for agriculture. 80% of Arizona’s allocation is used for irrigating agriculture, and almost California’s entire portion is for growing crops in the Imperial Valley.

The Imperial Valley and the Coachella Valley are some of the most productive agriculture areas in the world with nearly 500,000 acres being irrigated producing nearly $1 billion in crops annually.

One out of every three jobs in the valley is dependent on the agriculture industry. You can see in this true color image the contrast between the irrigated crops and the desolate desert surrounding them.

Water diverted from the Colorado River is entirely responsible for this landscape. Even the Salton Sea is a historical artifact filled with flows from the river. Notice the change in vegetation that occurs at the border.

Since 1942, the valley has received its water through the 82-mile long All-American Canal that carries water from the Colorado River in Arizona along the Mexico-California border to the California agricultural valleys.

Figure 9. The All-American Canal

Figure 10. This photo of the All  American Canal was taken  by the crew of expedition 18 aboard the  International Space Station.

Notice that the All American Canal is mostly an earthen canal that is uncovered and flowing through a sandy desert. The inefficiencies of the canal mean that it loses water to high evaporation rates as well as seepage through the sandy soil. Mexican farmers would take advantage of this recharge to the groundwater system and pump it up to water their own crops on the Mexico side of the region. However, California noticed the amount of water they were losing and has since decided to line portions of the canal, effectively conserving that water available to them and decreasing the amount available to Mexican farmers.


Your assignment for this part of the module is to learn about what is grown using Colorado River water. Search the internet, look at the produce and labels in your store, and research agricultural periodicals. What crops are grown in the Imperial Valley and other regions using the river’s water? Who eats those crops or where are they shipped? Can you find these crops at your local store? How many people are fed with this water? You may not be able to find all the answers to these questions, but you should get an idea of the river’s contribution to people as a food supply and an industry. How will a change in the amount of water available make a difference to you or other people? Once you understand the extent of the impact, identify adaptation measures that can be taken to sustain agriculture in a drier climate. How is adapting to climate change different from mitigation climate change?  Are any of the adaptation measures you identified also mitigation strategies?

Click here to download Part Two as a PDF

Part Three

The last section demonstrated the importance of the Colorado River water for agriculture. The amount of food produced and people employed because of the river cannot be understated. However, there are other users that compete with farmers for their share of the river water. As less water flows down the river, competition becomes fiercer. Is there anything more important than guaranteeing water for our food supply? 

Urban Growth in the Southwest

The Southwest has been one of the fastest growing regions in the United States over the past decade. Las Vegas and Phoenix have both experienced unprecedented growth. Other cities that are dependent on the river’s water include Tucson, San Diego, and Denver – all of which are still growing.  

Figure 11. Las Vegas Valley 1984  on left, 2009 on right.  Look for landmarks to show where the city  limits have grown (the airport, Red Rock Canyon, the playa at the top  middle of the picture).  (Source)

In Colorado, 80% of the water is deposited on the west side of the Rockies, but 80% of the state’s population is on the east side of the continental divide. This means that 22% of the Upper Basin water is moved over the divide to where the majority of the state’s population resides. The competition over water between urban centers and agriculture is explained in the water supply video by the Colorado River District at http://www.crwcd.org/page_315 .  

Western water law is governed by the Law of Prior Appropriation. Another way of putting it is first in time, first in right or first come, first served. The history of the country is told by its farmers. The landscape was a checkerboard of crops before big urban centers were built with their exploded suburbs. This means that the first water rights in the area belonged to the farmers and are still held as part of grower’s cooperatives. The fact that the municipal claims for water are newer means that in case of drought, they are susceptible to having their water cut off in order to assure that the farmers’ claims are met. Realistically, the number of people in modern cities lends them more political clout should a legal battle over water rights ensue.  

However, even without a legal battle, the competition between urban use and agricultural use has had impacts in other ways. The City of Los Angeles has taken to leasing water rights from farmers during drought years. They pay the farmers to not grow food, so that the city can use the water. There are also water speculation markets that are emerging. In anticipation of a demand for a bedroom community, developers will go around and buy up the water rights from farmers and then pay to pipe that water to a new location where they will build a new master community. Another way cities impact the demand for water is through their increased use of energy.  

Water’s Role in Energy Production

Figure 12. This image shows the  Navajo Generating Station just off the Colorado River near Page,  Arizona. (Source)

More urban centers mean more of a demand for electricity. For the Upper Basin, that means more water used in extracting oil from the ground to be used for gas for cars or burned in plants for electricity. Most power plants use water as a coolant. The steam from the water is then pressurized and pushed through a turbine, which creates electricity. Whether it is a nuclear power, coal, oil, natural gas, or even thermal solar power plant, they all need water as part of the energy production process.  

Coal plants also use water as part of the process to scrub pollutants out of the emissions. The water reacts with the particle in the smoke stacks and takes a percentage of nitrogen oxides and sulfur oxides out of the air. The plants can do this process without water, but it is more costly and less efficient. Coal plants are provide a feedback loop in the process. Since the coal plants also emit a lot of carbon dioxide in the smoke stacks, they are increasing the global temperature thus decreasing the snowpack of the Rockies and the water supply that they draw from in order to produce electricity from burning coal.  

In the 2000’s there were over 3800 MW of electricity production from burning coal that were planned as part of several different coal plants in Nevada, which already gets 50% of its power from in state coal plants. A 500 megawatt coal plant uses 2.2 billion gallons of water a year. Colorado currently receives 70% of its power from coal burning plants and has proposals for over 2000 MW of coal produced electricity planned to be built soon. New Mexico gets 90% of its power from coal and has plans for 1800 MW more. Utah gets 95% of its energy from coal-fired plants with plans for 750 MW more and Wyoming gets 96% of its power from coal with plans for 1400 MW more.  

Alternatives to coal power production in the area include hydroelectric, solar thermal and photovoltaic arrays. While these are clean sources of power production that do not increase the impact of climate change in the area, both hydroelectric and solar thermal power plants have an ongoing demand for water.  


Look up growth rates for urban centers in the Southwest. What have been the recent growth rates and the projected growth rates for Phoenix, Las Vegas, Denver, San Diego, others? What has been the growth rate and projected growth for energy demand for those areas? Identify mitigation strategies that can help keep the impacts of climate change to a minimum while still providing for the energy demands of these urban centers? Can these strategies also be considered adaptation strategies for climate change as well? Explain your answer.

Click here to download Part Three as a PDF

Part Four

Figure 13. (Source)

Figure 14. (Source)

The first sections of this module have illustrated the competition for water between farmers and urbanites. Now we will look closer at whom else we share the water with. 1.5 Million Acre Feet per Year are delivered to Mexico. However, the quality of the water is drastically different than what is used further up river. As the water flows over and through rocks, salts and minerals are eroded and added to the water. The concentrations of these then build up the further down river you go. Since lakes lose more water to evaporation than rivers do, the salinity of the water continues to increase after every dam. Salty water means salty soils for farmers and a common method for overcoming the salt is to add more water to try and dilute the salts in the soil. However, if the additional water evaporates out, it leaves more salt behind; there by adding to the problem it was meant to diminish. Saline soils means a decline in crop production.

The figure on the left shows the California-Mexico border. The image is shown using near infrared bands of the electromagnetic spectrum to highlight the green vegetation (crops), which show up as bright red in the image. Notice the drastic change that occurs at the Mexican border. At any given point in time, only about half of the arable land in the Mexicali Valley is cultivated due to a lack of sufficient water. Due to the salinity of the water, crops are currently experiencing a 10-15% decline in production.

The figure to the right is an image using different color bands and shows the lower half of the Mexicali Valley. The Colorado River is the dark blue patch at the top central part of the picture. Urban sprawl and irrigation siphon off most of the river before it reaches Mexico. In fact, only about 10% of all the river water makes it to the Mexican border, and that is then used before it reaches the delta where it would historically flow into the Gulf of California. The purplish flow from the gulf is where the ocean water is actually flowing up the river channel. The grey areas to either side of the delta are the historic sediment deposits from when the river carried sediments in its raging current to be deposited here at the mouth of the river. Now most of the sediments are trapped by large dams and the river sinks into the sand before it reaches the coast.  

This upset in the natural flow of the water and the disruption of the balance of sediment erosion and deposition has changed the ecology of the river delta. Not only has it left coastal villages dry, but it has caused several species to struggle for existence as well. Birds, marine life, and creatures adapted to the salt water marshes of the delta are all left struggling as the environment changes from the one they adapted to into something different. When we divide up a resource among different states and communities, we need to remember that it is not just humans who use these resources. Can we afford to live at the expense of other living creatures?


Should Lake Mead fall to 1,075 ft above sea level, the federal government would cut the water to seven states that depend on the Colorado River, according to an agreement they all signed in 2007. If that happens, the states would likely renegotiate the 1922 pact that establishes how the water is to be allocated. The current lake level is 1099 feet.  

Your final assignment is to discuss what that renegotiated compact should include. How much will we have to share? Who will we share it with? For what purpose should the water be used? Will it be sustainable in the face of growing populations and uncertain climate? How can we make our water use sustainable? Are there any conditions that need to be met before different user groups can use the water? The original pact for the river was made in 1922. What changes have occurred that would support changes in the pact today? Remember that the river is a system where all the water is allocated and there is less water available as a whole. Giving more water to any one area or user group means less water available for everyone else.  

Click here to download Part Four as a PDF


This module has been used as part of an on-line course as well as a lecture style class.  Students have demonstrated that they are not very good at interpreting graphs, so it is recommended that if the first section is not done in class, a follow up should be done with the students to go over the data, the trends that can be identified, and their significance to climate change. There is a 20 year trend that can be identified showing less snowpack the last couple decades. Managing that trend as a drought or as climate change has long lasting impacts.

Adaptation and mitigation are not explicitly defined in the module.  The module also requires students to do their own research on what strategies can be used by different user groups.  It is expected that this module is a part of larger course that has introduced some of these examples and definitions.

Further Reading/References

Funded by NASA Global Climate Change Education Grant NNXO9AL64G.

Return to the NCSE-NASA Interdisciplinary Climate Change Education homepage


Patricia Mynster, David Hassenzahl PhD (Lead Author);Andy Jorgensen (Topic Editor) "NCSE-NASA Curriculum Module - Colorado River water supply". In: Encyclopedia of Earth. Eds. Cutler J. Cleveland (Washington, D.C.: Environmental Information Coalition, National Council for Science and the Environment). [First published in the Encyclopedia of Earth July 28, 2010; Last revised Date April 14, 2011; Retrieved June 1, 2011 <http://www.eoearth.org/article/NCSE-NASA_Curriculum_Module_-_Colorado_River_water_supply>



Mynster, T. (2012). Colorado River water supply . Retrieved from http://www.eoearth.org/view/teachingunit/51cbf14c7896bb431f6a5047


To add a comment, please Log In.