Studies of climatic variability are attracting unprecedented attention from those who manage natural resources. Whereas in the past the primary climatic variables of direct importance to humans (precipitation, temperature) have seemed essentially random variables for any given month or season at any given place, climatologists now have shown convincingly that previously unknown deterministic elements underlie climate variability. These deterministic elements, which are associated with the so-called climate forcing phenomena, can, through statistical analysis, produce some degree of predictability where climate forcing has strong effects. Even more exciting is the prospect that a fundamental understanding of climate forcing mechanisms may produce...

Water has always been a precious resource in the American West. Consequently, variations in climate—which play a crucial role in both water supply and demand—have had profound social, economic, and environmental consequences for the region. Extended periods of above-normal precipitation have provided ample water supplies to meet consumptive and agricultural water needs, as well as to sustain and perhaps even promote population growth. Conversely, periods of extended drought have exposed major vulnerabilities in both human and natural systems. With rapid population growth projected to continue for the foreseeable future, the effective management of water resources will become even...

Variability in a renewable natural resource such as water can manifest itself in many ways, both spatially and temporally. In the American West the use of water resources typically was initiated and often then perpetuated with only cursory consideration or understanding of its variations in space and time. Even now, the spatial field of a climatic variable changing in time has barely been described and is not explained or incorporated into planning or operations involving water management.

Strong seasonality in precipitation exists throughout the western United States, much of which must be described in context with elevation (Redmond 1994). The...

It is important to place twentieth-century climate events, such as the Dust Bowl drought of the 1930s, into perspective so that their relative severity can be assessed. This can be done to an extent with the existing instrumental record. For example, although the southern Great Plains drought in 1998 had a severe effect on the economies of Texas and Oklahoma, costing $6 billion in Texas alone, the physical characteristics of that drought (spatial extent and duration) pale in comparison to the 1950s drought (Plate 8). The Dust Bowl drought of the 1930s was even more severe in terms of coverage...

Archives of data on climate, if reflective of rigorous standards and accompanied by appropriate supplementary documentation, can be used for multiple purposes ranging from testing of hypotheses about climate functions to improving regional resource management. Although numerous data archives exist, experience has demonstrated difficulties with their use and the need for various improvements in collection and archiving of data, as well as with data retrieval and manipulation. These issues were considered as part of a workshop in Boulder, Colorado, on June 21–22, 1999, that included contributions from individuals familiar with collection, archiving, analysis, and application of climate data. This...

Prediction of climate even at very high levels of accuracy is of little direct use to water managers without a reliable linkage between climate predictions and hydrologic predictions. Connections between climate and hydrology have been available for some time in relatively crude forms, such as the correlation between snowpack on specific dates and amount of runoff in the following months. Presently, a number of intensive efforts are under way to improve the sophistication and scope of the linkage between climate and hydrology. Clark and colleagues (Chapter 5) give an excellent overview of the present methods for forecasting water supply from...

Water in the West is allocated among diverse uses and is subject to mounting demand caused by a growing population and changes in institutional practices (Pulwarty 1995; Diaz and Anderson 1995). Demand coupled with climate variability and potential climate change presents formidable challenges for water managers. For example, the U.S. Bureau of Reclamation has indicated that if the West were to experience a drought similar to that of 1931–1940, the water needs of the lower Colorado River basin would not be met (el-Ashry and Gibbons 1988). These concerns have stimulated attempts to develop better water-management tools and improved information...

This chapter describes the effect of climate change on river runoff over the western United States, with the recognition that water resources play a key role in socioeconomic development in this region. The present analysis addresses the sensitivity of hydrologic resources, aquatic ecosystems, and water-management institutions to climate change. A variety of modeling approaches were used in the analysis, the goal of which is to provide decision makers with an understanding of the types of hydrologic effects that climate change may impose on hydrologic systems, management of water, and environmental resources in the western United States.

Few regional-scale investigations of...

In the western United States, water is a scarce and often limiting resource. Growth of human population and changing operational priorities both within the region and elsewhere have created pressure for more efficient management of water. Many management efforts focus—with considerable justification—on managing water demand and developing better tools, such as water marketing, that have the potential to reduce conflicts over water. Management of water supply is more problematic, as the total amount of available reservoir storage for beneficial use is constrained; opportunities for creating additional storage facilities that might help align supply and demand in terms of...

This chapter reports the main results of a workshop held in Boulder, Colorado, on June 21–22, 1999. The workshop dealt with the development potential for water-resources modeling based on climate and hydrology. The workshop participants, who represented a range of expertise in the field of water-resources management and water-resources modeling, were asked to consider whether coupled hydrologic and climatic models have substantial undeveloped potential or whether the main causes of variation that could be useful in modeling have already been exploited to the fullest extent possible.

The workshop participants first created a framework for evaluating the basis for modeling...

Water managers are well aware of recent advances in the prediction of climate and of the possibility of change in climate. Just as they have used other new technologies, they are prepared to use climate predictions as a component of management, and some have already begun to do so. A number of barriers to the full assimilation of climate-prediction capabilities into water management remain, however. The main difficulties involve institutional inertia, technology transfer, and the uncertain credibility of predictions. The chapters in this section address each of these issues.

Stakhiv’s chapter deals with institutional factors based on his long experience...

Adaptation to climate variability and change will require that all levels of government and all sectors of the economy respond in many ways. Sound management of water resources is central to the efficient functioning of many water-dependent activities—especially transportation (navigation), energy (hydropower), and agriculture. Advances in water management are especially critical for meeting the basic need for drinking water supply of our populace and for sustaining aquatic ecosystems, which would be particularly threatened if the most severe of possible climate scenarios were to materialize (Stakhiv and Major 1997).

The evidence for global climate change has been adequately covered in...

The Colorado River basin drains over 240,000 square miles (647,500 square kilometers) of the western United States. Its main stem originates in Colorado just west of Boulder; its four major tributaries are the Green, Gunnison, San Juan, and Gila Rivers. The basin covers portions of seven states (Wyoming, Colorado, Utah, New Mexico, Arizona, California, and Nevada) and drains into the Gulf of California in Mexico.

The Colorado River is the major source of water for consumptive use (about 12.5 million acre feet per year, or 1.54×10¹⁰ m³ per year) in the seven states. Ten major reservoirs lie within the basin,...

These words of Thomas Hornsby Ferril, Colorado’s poet laureate in 1940, are etched in the rotunda of the State Capitol Building in Denver. Colorado’s pioneers carved their water legacy in the earth when they developed an intricate web of irrigation ditches across the state. Today, water providers continue that tradition by tapping into nature’s riches to provide dependable water supplies for a wide range of uses.

Colorado irrigators have struggled with the state’s climate for centuries. Although extensive irrigation did not begin in Colorado until the mid-1800s, ancient cliff dwellers in the arid southwestern part of the state developed irrigation...

Water managers are uniquely qualified to evaluate the utility of current and proposed climatic predictions that can be related to availability of and demand for water. A workshop for water managers in Boulder, Colorado, on June 21–22, 1999, provided an unusual opportunity to gather information from water managers about the current and future uses of predictions. The outcome of the workshop for water managers is summarized here through their responses to a series of questions concerning current, anticipated, and ideal means by which climatic predictions and their hydrologic and water-demand correlates can be used. The workshop participants gave a...

The framework within which human adaptation to climate variability must occur in the West consists most visibly of water-management institutions, as described in Part 3. A less visible but no less important part of the framework consists of institutions and societal forces that are not directly connected to water management but nevertheless influence it powerfully. These include demographic trends, land-use management, water and environmental law, economic and commercial systems for exchange and distribution of water, and a network of organizations that either make or influence policy in ways that will affect distribution and use of water. The four chapters in...

The Interior West stands out in any geographic analysis of U.S. regions for a number of reasons. Physically, the region encompasses the most mountainous terrain in the contiguous United States, from the broad swath of the Rocky Mountains to the multiple ranges of the Basin and Range province. The landscape is also politically atypical because roughly half of the land is in federal ownership. Socially, portions of the West are among the fastest-growing regions of the country, especially in the last decade. The eleven western states grew by 10.2 million people in the 1990s, or 20 percent, compared with a...

A quiet revolution has been taking place in western water policy. By the 1980s, western water law seemed outmoded, and states promised reform to satisfy changing public demands and values. The 1990s brought change, but it came largely through initiatives of the federal government and local communities. Meanwhile, state water law and policy evolved haltingly at best.

During the last quarter of the twentieth century, urbanization and society’s aroused environmental consciousness put new demands on an old, unyielding system. The water distribution regime was dominated by unadorned notions of legal rights rooted in prior appropriation and by physical facilities, consisting...

This chapter presents an overview and synthesis of policy tools that state and federal agencies can use to assist water managers in adapting to climatically driven variability in water demand and supply. Some of these policy tools can also help address the current conflicts in water demand, supply, and valuation between traditional water uses and newer, growing uses.

Off-stream water use in the United States increased over tenfold during the twentieth century in response to population and economic growth (Brown 1999). Growth is expected to continue in the western United States, and domestic and commercial demands for water probably will...

A great deal has been learned about climate and its variability in the West over the past several decades (Chapter 1). We have extended the period of hydrologic records from a few decades to well over a century (Chapter 3). This longer period of record has contributed to our appreciation of the nature and extent of climate variability and its effects on water resources. Furthermore, substantial scientific and technical advances are increasing our understanding of the mechanisms and processes (local, regional, and global) underlying variation in climate. Scientific advances are contributing to our ability to predict future variability of climate....

The knowledge that one is going to have the last word at a conference dealing with a subject as complicated as this one gets the neurotransmitters stirred up in a very memorable way. As a western American historian, I am a fascinated observer of the role of experts in natural-resource management, and so the assignment to listen closely and offer concluding remarks at this conference was an honor and a pleasure. On this occasion and others like it, I steer by the hope that commentary from the humanities can offer natural scientists an opportunity to step away from the detail...