The Severe Sustained Drought Study
Overview
Excerpted from Young
The suggestion for an interdisciplinary research program to study the impacts of a severe sustained drought in the southwestern U.S. arose at a conference sponsored by the Arid and Semi-Arid Lands Directorate of the Man and the Biosphere Program, U.S. Department of State, held at Monterey, California, in 1982. One of the Conference panelists, Dr. Harold Fritts of the Laboratory for Tree Ring Research, University of Arizona, presented tree ring evidence from the southwestern U.S. implying that much more extreme and extended droughts were experienced in the past several centuries than have been observed in the modern records. Professor Gilbert F. White of the University of Colorado amplified upon this theme in his summary and overview remarks at the close of the conference, and among other points urged the importance to the southwest of anticipating and preparing for severe and sustained droughts.
An interdisciplinary team of researchers from universities in the Colorado River Basin states developed a two-phase approach, and the Man and the Biosphere Program supported the first phase work. The Phase I report (Gregg and Getches, 1991) provided initial analyses of tree ring evidence for severe sustained droughts in the southwest, and it included studies of the hydrologic and water quality implications, as well as initiating legal, political, and economic analyses of the ramifications of coping with such droughts.
The present analysis extends the earlier Phase I studies with a series of detailed impact assessments and modeling studies, complemented by formal policy evaluations. It was conducted by an inter-disciplinary team from the Universities of Arizona, California, Colorado, Nevada, and Wyoming, plus faculty at Colorado State and Utah State Universities and the consulting firm Hydrosphere, Inc., based in Boulder, Colorado.
Taking the present-day configuration of the storage and diversion structures and the economic conditions in the Basin as the base-point, the general objectives of the present Phase II study were three: first, to assess the hydrologic impacts of a Severe Sustained Drought (SSD); second, to forecast the economic, social, and environmental impacts on the southwestern U.S.; and finally, to assess potential alternative institutional arrangements for coping with an SSD. The papers collected here are largely condensations and revisions of the chapters appearing in the Phase II project completion report (Young, 1994).
The research team believes that this effort is unique in a number of ways. Most drought assessments have been retrospective, seeking to assess the negative impacts after the fact and to describe human responses and adjustments to drought (Warrick, 1975; Easterling and Riebsame, 1987). Such studies provide valuable understandings of the consequences of drought and help planning for mitigation of future drought periods. The present study attempts to employ modeling to anticipate impacts of droughts and to assess alternative policy responses.
The initial step was to select a representative SSD for study. Drought is defined differently by differently disciplines, and the choice of a study drought required careful consideration. Numerous definitions of drought have been proposed (Wilhite and Glantz, 1987). One approach defines drought in meteorological terms - e.g., as limited or no rainfall within some specified time period. However, such a method cannot distinguish between drought and general aridity. Agriculturally or ecologically-oriented approaches focus on shortages of soil moisture relative to plant evapotranspiration needs, while the hydrologic approach might employ streamflow or groundwater levels relative to long-term averages.
Most definitions, as well as common usage, share the point that drought is a situation of scarcity relative to "normal" conditions of precipitation, evapotranspiration, or river flow. Drought refers to an occasional situation, not permanent scarcity. Further, a definition of drought must be based partly on demand-side, human considerations, not solely on meteorological or hydrologic factors. However, no general agreement exists to guide the selection of a definition.
For this study, we chose a hydrologic measure as our basic indicator of drought: river flows relative to long-term averages. However, the hydrologic measure was derived from tree ring studies of long-term climatic behavior.
The representative 38-year drought period adopted for this study is patterned after (but not identical to) the most severe and long-lasting dry period identified by the tree ring studies. The drought chosen for evaluation includes a period of unusually low flows lasting about two decades, followed by a period of high flows long enough for mean annual inflow to return to its long-term average.
"The Tree-Ring Record of Severe Sustained Drought in the Southwest," by dendrochronologists David Meko, Charles W. Stockton and W. R. Boggess, reviews the tree ring record of severe droughts in the southwestern U.S.
David G. Tarboton's contribution, "Hydrologic Scenarios for Severe Sustained Drought in the Southwestern United States" develops hydrologic scenarios of regional water shortage to be used in the broader study of the economic, political, social, and environmental impacts of severe sustained drought in the southwestern U.S.
In the next paper, "Impacts of a Severe Sustained Drought on Colorado River Water Resources," by Benjamin L. Harding, Taiye B. Sangoyomi, and Elizabeth A. Payton investigate the hydrologic impacts of the most severe drought reconstructed by Tarboton (1995), taking account of the existing human-made structures and institutional arrangements.
Following these hydrologic studies, the second section of the issue consists of two articles which address legal, administrative, and political aspects of the problem and one reporting on the social impact studies.
"The Law of the Colorado River: Coping With Severe Sustained Drought" - from the perspective of its effect on water allocation decisions - is the subject of the analysis by legal scholars Lawrence J. MacDonnell, David H. Getches, and William C. Hugenberg, Jr. They present an interpretation of how water would be allocated according to existing legal priority during a severe sustained drought episode.
In the next article, "Institutional Options for the Colorado River," Douglas S. Kenney examines institutional options from the perspective of political science and public administration.
In "Social Implications of Severe Sustained Drought: Case Studies in California and Colorado," Richard S. Krannich, Sean P. Kennan, Michael S. Walker, and Donald L. Hardesty developed social impact indicators or drought.
The third section of the issue contains two impact analysis studies, which present environmental and economic impact assessments of the effects of a severe sustained drought, and three modeling studies, which integrate instream and offstream considerations and tests of alternative policies.
In "Assessing Environmental Effects of Severe Sustained Drought," the first impact analysis study, Thomas B. Hardy describes his derivation of the environmental impact measures employed by the basin models of impacts used in the subsequent gaming exercises.
In "Competing Water Uses in the Southwestern United States: Valuing Drought Damages," the second impact analysis study, economists James F. Booker and Bonnie G. Colby summarize the measures developed to assess economic losses from drought.
In "Hydrologic and Economic Impacts of Drought Under Alternative Policy Responses," the first modeling study, James F. Booker describes the formulation and operation of the Colorado River Institutional Model (CRIM), an optimization model integrating hydrologic, economic, and legal-institutional elements pertinent to managing Colorado River waters.
In "A Gaming Evaluation of Colorado River Drought Management Institutional Options," the second modeling study, James L. Henderson and William B. Lord adopt the technique of real-time simulation and gaming experiments to analyze changes in operating rules for allocating and managing Colorado River water which could help reduce adverse impacts of a severe sustained drought.
In the last of the modeling studies "Mitigating Impacts of a Severe Sustained Drought on Colorado River Water Resources," Taiye B. Sangoyomi and Benjamin L. Harding employ hydrologic simulations to assess the hydrologic implications of several of the drought-coping responses developed in the interactive gaming exercises reported by Henderson and Lord (1995).
In the concluding paper, "Managing the Colorado River in a Severe Sustained Drought: An Evaluation of Institutional Options," by William B. Lord, James F. Booker, Benjamin L. Harding, Douglas S. Kenney, and Robert A. Young, the findings, conclusions, and recommendations of the Phase II study are summarized. These findings, conclusions, and recommendations fall into three groups: those which pertain to the operating rules presently in effect; those pertaining to potential changes in existing rules; and those which pertain to the feasibility of making such changes via negotiation, litigation, or legislation.