Tribes in Arizona have senior rights to much of the surface water in the state — rights the tribes have fought long and hard to protect. A significant portion of the water used to satisfy these tribal rights comes from the Colorado River.
Will there be enough water in the river in the coming decades to honor tribal rights, as well as meet the demands of other water users?
Nobody knows the answer to that question. What is clear is that a growing body of research points to a substantial reduction in the Colorado’s flow. Climate change, combined with natural variations from year-to-year, seems very likely to reduce the amount of water in the river over the coming decades.
The physical processes driving the projections of less water are well known. Much of the flow in the Colorado originates as snowpack in the high Rockies. Rising temperatures attributed to climate change reduces the snowpack. Runoff from the snowpack occurs earlier in the year. More precipitation falls as rain, rather than snow. Higher temperatures increase the evaporation of moisture back into the air.
Over the last five years there have been a number of scientific studies that have attempted to project the effect of these factors on the streamflow in the Colorado River system. All of them foresee reductions in runoff and resulting streamflow in the range of 10% to 20% by the middle of this century. Work is currently underway to reconcile the differences in these projections.
The river’s flow has averaged about 15 million acre-feet (maf) over the last 100 years. This means that a 10% reduction would amount to about 1.5 maf (for a total flow of 13.5 maf). A 20% reduction would amount to 3 maf (for a total flow of 12 maf).
The water in the river is currently overallocated. The 1922 compact dividing the river’s flow gives 7.5 maf to the Lower Basin states of Arizona, California and Nevada. The Upper Basin states of Colorado, New Mexico, Utah, Wyoming and a small portion of Arizona are allocated 7.5 maf. In addition, Mexico has treaty rights to 1.5 maf. These all add up to a total allocation of 16.5 maf.
In this context, the scientific projections of a significantly reduced flow over the next three to five decades present serious concerns for all who use Colorado River water.
There are a number of studies projecting future flow in the Colorado, but there is much less research on what climate change might do to the other rivers in Arizona. One study by researchers at ASU did look at the Salt and Verde Rivers. That research reached the same overall conclusion as did the studies of the Colorado. In the future, there will be less water in these streams.
The Colorado River is one of the most extensively managed bodies of water in the United States. Serving an estimated 30 million people and an area with roughly 3.5 million acres of farmland, most of it irrigated, the use of water in the River is controlled by a complex collection of laws, court decisions, interstate compacts and regulations. This body of documents is known collectively as the “Law of the River.”
Major elements of the Law of the River include:
● The Colorado River Compact of 1922, the interstate agreement, ratified by the federal government, that divided the rights to water in the river between the Upper Basin states of Wyoming, Colorado, Utah and New Mexico and the Lower Basin states of Arizona, Nevada and California.
● The Boulder Canyon Project Act of 1928, which not only authorized the construction of Hoover Dam, but also apportioned the water available to the Lower Basin among the three states involved.
● The Arizona v. California US Supreme Court Decision of 1964, which finally settled a 25-year dispute between the two states over their competing claims to the River. The decision also perfected the legal rights of five Colorado River tribes to their share of the water.
● The Colorado River Basin Project Act of 1968, which authorized the construction of the Central Arizona Project.
● Treaty agreements between the United States and Mexico providing for Mexico’s rights to a share of the water in the River.
All of these documents and more can be found on the Law of the River page of the Web site of the Lower Colorado Region of the US Bureau of Reclamation. The full text of each is available for downloading.
The Web address is: http://www.usbr.gov/lc/region/pao/lawofrvr.html
The US Bureau of Reclamation developed a massive Environmental Impact Statement as an important part of the process of drafting interim guidelines to govern the management of the Lower Colorado River in times of shortage. The Final Environmental Impact Statement (FEIS) was published in October of 2007, shortly before the decision on the guidelines was signed.
Although devoted to the discussion of issues involving the shortage guidelines, the FEIS is a major compendium of information on the Colorado River. It discusses the hydrology of the river, releases from the major reservoirs of Lake Mead and Lake Powell, water deliveries, electrical power generation and recreation uses of the River, among other topics.
The FEIS includes 21 appendices, covering such subjects as entitlements to River water in the states of Arizona, Nevada and California, projected depletion schedules through 2060 for each Lower Basin user, River system facilities from Lake Powell to the southernmost boundary between Arizona and Mexico and contains extensive data on the agricultural economy of the counties in Arizona along the River or served by River water. Although climate change projections were not used in making the final decision on the shortage guidelines, one appendix is devoted to the subject.
The FEIS also includes a section containing the comments on the draft of the Environmental Impact Statement submitted on behalf of tribes and Reclamation’s response to each comment.
The Lower Colorado Region of the Bureau of Reclamation website contains a full listing of all the sections of the FEIS and provides an opportunity to download each section.[this is the link for the website mentioned above http://www.usbr.gov/lc/region/programs/strategies/FEIS/index.html]
[Link to the Record of Decision. Colorado River Interim Guidelines for Lower Basin Shortages and the Coordinated Operations for Lake Powell and Lake Mead December 2007 PDF]
In December of 2007 the Secretary of the Interior and Commissioner of Interior’s Bureau of Reclamation signed a “Record of Decision” establishing guidelines for how the Colorado River would be managed in times of shortage.
This marked the first time that the federal government and the seven Colorado River Basin states have agreed on how to handle situations when the River cannot deliver all the water legally promised to users. The final decision on the shortage criteria was developed after two-and-a-half years of discussion and negotiation, primarily among the states in the Basin.
The guidelines lay out the circumstances under which an official shortage situation is declared and how the shortfall in available water is to be shared among the states of Arizona, Nevada and California.
They also provide for the coordinated operation of Lake Mead, which stores water for release to Lower Basin users, and Lake Powell, which stores water for release to the Lower Basin. The purpose of controlling the reservoirs in tandem is to prevent either one from becoming too low to fulfill its role in the management of the River’s flows.
The guidelines also created incentives for users in the Lower Basin to conserve water to which they are entitled in Lake Mead, in part to avoid a shortage situation. These incentives are usually referred to as “Intentionally Created Surplus” or ICS programs.
The shortage guidelines are referred to as “Interim” because they are intended to govern the management of the River only through the year 2026.
A copy of the Record of Decision is available on this Web site. Click on the link to the “Interim Shortage Guidelines.”
The Record of Decision is based on an extensive Final Environmental Impact Statement, which is described in a separate item in this section of the Web site.