Colorado River Basin Water Management
Evaluating and Adjusting to Hydroclimatic Variability
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NOTICE: The project that is the subject of this report was approved by the Governing Board of the National Research Council, whose members are drawn from the councils of the National Academy of Sciences, the National Academy of Engineering, and the Institute of Medicine. The members of the panel responsible for the report were chosen for their special competences and with regard for appropriate balance.
Support for this study was provided by the National Research Council’s Day Fund, the U.S. Bureau of Reclamation under contract number 05PG303309, the California Department of Water Resources, the Metropolitan Water District of Southern California under contract number 77624, and the Southern Nevada Water Authority. Any opinions, findings, conclusions, or recommendations expressed in this publication are those of the author(s) and do not necessarily reflect the views of the organizations or agencies that provided support for the project.
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Cover: Tree-ring cross section photograph courtesy of Connie Woodhouse. Glen Canyon Dam and Lake Powell (2004) photograph courtesy of Brad Udall. Skyline photograph of Las Vegas, NV provided by the U.S. Bureau of Reclamation at http://www.usbr.gov/dataweb/html/ griffith.html. Formal portrait of John Wesley Powell circa 1890’s from the U.S. National Park Service’s Grand Canyon National Park Museum Collection.
Copyright 2007 by the National Academy of Sciences. All rights reserved.
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COMMITTEE ON THE SCIENTIFIC BASES OF COLORADO RIVER BASIN WATER MANAGEMENT*
ERNEST T. SMERDON, Chair,
University of Arizona (Emeritus), Tucson
JULIO L. BETANCOURT,
United States Geological Survey, Tucson, Arizona
GORDON W. “JEFF” FASSETT,
HDR Engineering, Inc., Cheyenne, Wyoming
LUIS A. GARCIA,
Colorado State University, Fort Collins
DONALD C. JACKSON,
Lafayette College, Easton, Pennsylvania
DENNIS P. LETTENMAIER,
University of Washington, Seattle
ELUID L. MARTINEZ,
Water Resources Management Consultants, Santa Fe, New Mexico
STEPHEN C. McCAFFREY,
University of the Pacific, Sacramento, California
EUGENE M. RASMUSSON,
University of Maryland (Emeritus), College Park
KELLY T. REDMOND,
Desert Research Institute, Reno, Nevada
PHILIP M. SMITH,
Science Policy and Management, Santa Fe, New Mexico
CONNIE A. WOODHOUSE,
University of Arizona, Tucson
JEFFREY W. JACOBS, Study Director
DOROTHY K. WEIR, Research Associate
The Colorado River has long been uniquely important in the exploration, development, and culture of the western United States. The Colorado is a desert river, stretching from high in the Rockies, through great canyons and arid regions in Utah and Arizona, and finally ending in the Gulf of California in Mexico. For millions of years it has shaped landforms and in the Grand Canyon has exposed geologic formations that are half as old as the Earth itself. The great American scientist John Wesley Powell explored this region widely. He had extensive knowledge of many Native American tribes and his 1869 boating expedition down the Colorado River through the Grand Canyon is legendary. Powell’s 1878 publication Lands of the Arid Region of the United States, with a More Detailed Account of the Lands of Utah offered many new ideas regarding the roles of the U.S. federal government in developing western water supplies. Although Powell may have foreseen some aspects of western development, one thing he probably did not foresee was the future extent of population growth in the Colorado River region. Nor was Powell likely to have imagined that changes in regional climate might someday affect hydrologic conditions.
Our committee was asked to review the hydrologic and climatic bases of Colorado River water management. In considering this existing body of scientific information, we were struck by the warming across the region in the past century and by the fact that nearly all global climate models forecast increasing temperatures for the Colorado River region. We also noted the exceptionally hot and dry conditions across much of the nation in the summer of 2006, and that the 2006 average annual temperature for the contiguous United States was the warmest on record and nearly identical to the record
set in 1998. These conditions are consistent with warming trends in the region.
As we proceeded it became clear that a broad understanding of Colorado River water management issues is not possible unless both water supply and demand issues are adequately considered. Terms such as “population growth” and “water demand” did not appear in our statement of task. As we spoke with water experts from across the region at our meetings, however, they identified important linkages among hydrology and climate and issues such as population growth and water demands, urban water management and conservation, riparian ecology, and water transfers. Clearly, interest in hydroclimatic issues in the region is being driven in large part by increasing water demands and a limited ability to augment water supplies through traditional means. Furthermore, our statement of task called for us to consider the broad topics of systems operations and water management practices. We thus felt it incumbent upon us to comment on topics of water demand, technologies and practices for augmenting water supplies, and programs for coping with drought.
Our report presents population growth data for much of the western United States that is served by Colorado River water. The cities in the region are collectively the fastest growing in the nation. Of further concern is that this growth seems to be occurring with little regard to long-term availability of future water supplies. Ideally, these issues will be openly discussed and squarely addressed before the water supply-and-demand balance across the region becomes more critical. This is important because, for example, the drought of the early 2000s turned out to be even worse than many assumptions regarding a worst-case-scenario drought. This ongoing drought has contained a sequence of exceptionally dry years. Inflows into the basin’s storage reservoirs have been well below normal and it may take 15 years of average future hydrologic conditions to refill the basin’s largest water storage reservoirs, Lakes Mead and Powell. These hydroclimatic trends are especially troubling in light of rapidly increasing water demands.
I thank our committee members for the hard work and intellect they devoted to producing this consensus report. Each of them brought unique expertise to our deliberations and report preparation and they all devoted many hours of personal time to our study. Their views were fully considered in our study process and I thank them for
their contributions, good will, and spirit of collaboration. I also thank the many water scientists, engineers, administrators, and other experts from across the region that spoke with our committee. They provided a comprehensive and fascinating update of key water and science issues across the region and presented important topics and questions for our committee’s consideration, all of which were essential to our deliberations and report (Appendix B lists these speakers).
I also thank the National Research Council (NRC) staff members for their dedication and diligent work in our study process. Jeff Jacobs, senior staff officer with the Water Science and Technology Board (WSTB), ensured that our committee stayed on task and that the varying opinions and written contributions from our committee members were blended to create a single, coherent report. Jeff and the committee were ably assisted by WSTB research associate Dorothy Weir, who handled administrative details of the meetings and ably assisted in all phases of report preparation.
We are grateful to the sponsors who provided support for this study. These sponsors included federal, state, and municipal water organizations across the West, which reflects the broad interest in and importance of in these issues. These sponsors were the California Department of Water Resources, the Metropolitan Water District of Southern California, the Southern Nevada Water Authority, and the U.S. Bureau of Reclamation. We also thank the National Academies for providing a substantial portion of funding and for exercising leadership in initiating this study.
This report was reviewed in draft form by individuals chosen for their breadth of perspectives and technical expertise in accordance with the procedures approved by the National Academies’ Report Review Committee. The purpose of this independent review was to provide candid and critical comments to assist the institution in ensuring that its published report is scientifically credible and that it meets institutional standards for objectivity, evidence, and responsiveness to the study charge. The reviewer comments and draft manuscript remain confidential to protect the deliberative process. We thank the following reviewers for their helpful suggestions, all of which were considered and many of which were wholly or partly incorporated in the final report: John A. Dracup, University of California; Jerome B. Gilbert, Orinda, California; W.R. Gomes, University of California; Martin P. Hoerling, National Oceanic and
Atmospheric Administration; Malcolm K. Hughes, University of Arizona; Katharine L. Jacobs, University of Arizona; John W. Keys, III, Moab, Utah; Upmanu Lall, Columbia University; John E. Thorson, California Public Utilities Commission; and James L. Wescoat, Jr., University of Illinois.
Although these reviewers provided constructive comments and suggestions, they were not asked to endorse the report’s conclusions and recommendations nor did they see the final draft of the report before its release. The review of this report was overseen by Daniel P. Loucks, Cornell University, who was appointed by the NRC’s Report Review Committee, and by A. Dan Tarlock, Chicago Kent College of Law, who was appointed by the NRC’s Division on Earth and Life Studies. Drs. Loucks and Tarlock were responsible for ensuring that an independent examination of this report was conducted in accordance with NRC institutional procedures and that all review comments received full consideration. Responsibility for this report’s final contents rests entirely with the authoring committee and the NRC.
The seven Colorado River basin states and cooperating agencies, particularly the Bureau of Reclamation, face great challenges in addressing the complex issues of Colorado River water supply management. The pressures of meeting the needs of the burgeoning population in the face of future severe droughts and uncertain impacts of global change are indeed great. Political pressures will abound but there are signs of increasing cooperation on a variety of water use issues. We hope this report represents a contribution to the knowledge base of Colorado River hydroclimate and water management and that it helps promote common understanding and cooperation on these matters.
Ernest T. Smerdon