might be established on the drought-affected hilltops, and hybrid poplar saplings for wood products might be planted in the poorly drained low areas. Thus, the diversity of the new region would promote crop diversity as well (CAST 1992).

Another possible shift of the Corn Belt might be to the Dakotas. To the extent that moistening is less likely to accompany the warming than is drying, a shift to the Dakotas is less likely. Because soils there resemble those in the present Corn Belt, yields and the mixture of crops might stay much the same. In fact, yields might be higher in the "new" Corn Belt, if the long days in the north were combined with ideal temperature and precipitation.

A Corn Belt shift could entail large social and environmental costs. Some rural communities and their physical infrastructure could become obsolete or might need to be relocated. If climate change were gradual and anticipated, these transitional costs could be modest.

Genetic Diversity Banking

Genetic diversity is essential for successful breeding, whether for crops, animals, or trees. The base of genetic diversity is provided by a series of collections of present and previous varieties farmers have used. Maintained in special germ-plasm banks, these collections number in the tens of thousands for each major crop. When needed, they can be screened for sources

of resistance to new diseases and insects, tolerance of new kinds of environmental stress, or employment of new technological opportunities.

Plants growing in gardens and in native sites complement the germ-plasm banks. As climate changes, natural selection will proceed among diverse populations in native sites and will help breeders looking for new combinations to fit new climates. Because the germ plasm for the dozen or so crops that feed most people is concentrated in a few centers, managed preservation strategies will concentrate on these centers (Duvick 1984).

Government Facilitation of

Adaptation

The United States has recently taken several important steps that will help facilitate autonomous adaptation and increased productivity.

• The 1990 Food, Agriculture, Conservation, and Trade Act created new rules for farm

support payments that reduce the rigidity of farming practices.

• The 1992 Water Bill will encourage flexible transfer of water in California to the highest-value uses.

• The biotechnology oversight policy initiated in February 1992 and the rules on agricultural biotechnology proposed in November 1992 may help facilitate the development of genetic techniques for dramatically improved crops.

In the wake of each large flood, hurricane, or extended drought follow various socioeconomic and ecological impacts. Changes in global climate could significantly change pressures, both positively and negatively, on the quantity and quality of water supplies. Over the past two centuries, the nation's water resource

management agencies have worked to reduce the nation's vulnerability to the hydrologic extremes associated with climate variability.

In most regions of the United States, agriculture is the main consumer of water resources. No new major federal irrigation projects have been authorized since

1968, while new flood-control projects and coastal storm protection projects continue to be authorized on a regular basis. While the ongoing construction of major irrigation projects remains an important activity, it is declining (Figure 21), and spending continues to shift from construction to operations and maintenance. Once the three major federal irrigation projects currently under construction are complete, construction activities will be on a considerably smaller scale, unless major new projects are authorized in the near future. One major flood-control dam and reservoir is under construction, and another is in the planning stage.

Figure 21

Nevertheless, adaptive measures could be instituted to increase the flexibility of existing management regimes and, thus, increase the ability to respond quickly and inexpensively to changing conditions. Also, where technically, economically, and environmentally sound, new regimes could be constructed. These measures could include evaluating water supply systems, water transfers, water conservation measures, flood control, navigation, drought management, system optimization, global change research, and desalinization technologies.

Construction funding of major irrigation projects has declined principally because most of the best sites for major reservoirs have been used; the potential costs of construction at the remaining sites are high relative to expected benefits and to other alternative courses of action; federal and nonfederal budgets are strained; and water management projects are becoming increasingly controversial among environmental interests and a broader cross-section of the public interested in using streams in their free-flowing state for recreational uses and maintaining river valleys in their natural state.

In the past, when climate was assumed to be relatively constant (despite substantial year-to-year variations), managers could estimate new demands for water by evaluating measurable or observable factors-the rate of population growth, the rate of decline of groundwater supplies, or the degree of aridity in newly settled areas. For many years to come, the magnitude-and even the direction-of potential climate change are likely to be difficult to project at the regional level.

Water Supply Systems

Given the uncertainty over the nature of hydrologic changes to be expected in any particular region and the cost of significantly changing existing water supply systems, a logical step is to evaluate the flexibility of current systems to the types of impacts that might result from climate change and to examine the feasibility of providing new water management systems. Toward this end, the United States has implemented the following measures:4

• Initiated the development of an advanced decisionsupport system that will apply the latest technology to increase our understanding of and improve the effectiveness of river basin and water system operations. This technology is being transferred to five agencies in the Santa Anna River Basin of California. The United States also is developing agreements for the public use of this software.

• Formed a drought coordination team to serve as a clearinghouse for drought-related information and participated on a federal/state drought management

team.

• Established "AgriMet"-a cooperative information network that provides expanded data support for onfarm irrigation management and crop scheduling programs throughout the Pacific Northwest. Through regional analysis of the daily water use of crops, crop models translate real-time climate data from approximately forty sites into data for publication in local newspapers.

• Initiated reallocation studies of numerous U.S. reservoir systems. These studies examine the feasibility of shifting storage in reservoirs designed for various purposes (hydropower, flood control, navigation, irrigation, in-stream flows, municipal and industrial

water supply, and recreation) in direct response to changing needs in a given region.

• Initiated systems management studies of the Great Lakes region that explicitly take potential climate change into account. These studies analyze the response of the hydrologic system to assumed climate changes and assess the vulnerability of water management systems to those changes.

• Conducted several studies, in conjunction with municipalities and urban areas, that focus on options for managing increasing demand for water. The federal government has also developed a sophisticated water-demand model to assist in these analyses.

• Initiated a three-year study (now in its final year) to develop a template for drought planning and management studies. These “drought-preparedness studies" may recommend instituting water-demand-management measures as a first response to drought conditions.

Water Transfers

A promising approach to coping with changes in climate, whether due to natural variability or human activity, is to foster flexibility in water management institutions. One means of doing this is to facilitate market transfers of water. The recently enacted Reclamation Projects Authorization Adjustment Act of 1992 contains important provisions facilitating water transfers in California. A number of major public utilities supplying water have taken steps toward pricing systems that should ensure more efficient use. Others are studying marginal cost pricing.

The life of a water project is often fifty to one hundred years. No matter how well a project is planned, it would be impossible to accurately forecast the pattern of water demands over such a long period. Therefore, water transfers can provide a flexible means to accommodate new patterns of climate, agricultural production, population, and industrial growth without relatively major capital expenditures. Voluntary transfers may be particularly important in areas receiving relatively little rainfall or where existing sources are fully used.

Facilitating water transfers in the arid western United States is particularly important because of the large quantities of water currently required for agriculture-typically 85-90 percent of water withdrawn. This implies that urban and industrial uses of water can double their current 10-15 percent level through either modest conservation of irrigation supplies or small

reductions in the least productive agricultural uses. Market-based water transfers would give agricultural water users the incentive to do so willingly. For example, a 3 percent reduction in agricultural withdrawals in California would be equivalent to 3.47 billion liters (918 million gallons) of water per day-enough to supply the daily needs of 6.6 million urban users (roughly the size of Los Angeles).

Market transfers of water are not new. Water rentals in the system of federal storage reservoirs on the Upper Snake River in Idaho stretch back to the 1930s. In 1972, the Utah Power and Light Company obtained 6,000 acre-feet of water from two irrigation companies in the Emery County Project for power-plant cooling. The city of Casper in Wyoming is paying the nearby CasperAlcove Irrigation District to line the canal on portions of the district's distribution system. During the 1976-77 drought in California, the Bureau of Reclamation operated a water bank in which some 45,000 acre-feet of water changed hands. There is a highly organized market operating in the Northern Colorado Water Conservancy District in the Ft. Collins area, in which water from the Colorado Big-Thompson Project is exchanged at market value (Wahl and Osterhoudt 1986; NRLC 1991).

Two recent agreements between the Metropolitan Water District of Southern California (MWD) and the Imperial Irrigation District (IID) present a dramatic example of conservation possibilities. In late 1988, MWD struck an agreement with IID to fund conservation measures that would salvage 100,000 acre-feet of water annually for municipal and industrial uses in the MWD service area. Under the agreement, MWD will pay IID $92 million for the construction of conservation facilities, $3.1 million annually for operation and maintenance, and $23 million in five annual installments for indirect costs. Under a separate agreement, concrete lining of the All-American Canal (which carries water from the Colorado River to IID) will conserve another 70,000 acre-feet of water for use by MWD.

Studies by the federal government and the state of California estimate that there are additional water-conservation investments in the IID that could serve as the basis for future agreements. In addition, MWD recently signed an agreement with the Palos Verdes Irrigation District, whereby MWD would gain access to additional water supplies under certain conditions in exchange for payments to Palos Verdes irrigators. A number of recent settlements of Indian reserved-water-rights claims have also included provisions allowing the tribes to market their water rights to nearby communities. On the state level, some states have amended their water codes over the last ten years to facilitate transfers.

For example, because of amendments adopted in 1982, California law now ensures that an appropriator has the rights to water that it conserves; this water may be sold or leased to other water users without fear of a reduction of the original water right or alteration of the priority date of any claim to use the water. In 1979, Idaho passed state water banking legislation, ensuring that water users placing water in the bank would not be subject to forfeiture of their rights because of nonuse. The Oregon legislature also has passed legislation to give water users an incentive to conserve water. In New Mexico, salvaged water may be transferred if the applicant can demonstrate clearly that there is no impairment to other water-right holders, including junior appropriators (Wilkinson 1989).

In December 1988, the United States released a water transfer policy, outlining the principles the federal government would follow when facilitating voluntary water transactions. The policy statement was important for two reasons: (1) it acknowledged the importance of voluntary water transfers in meeting future water demands in the West, and (2) it stated that the federal government would be a facilitator of transactions among willing buyers and sellers.

However, very few of these transactions have taken place, partly because the rules are new and some aspects need clarification, and possibly because the rules have varied from one federal project to another. Also, many institutional and legal barriers need to be surmounted.

For example, in the large federally constructed Central Valley Project in California, only short-term (one year or less) transfers have been permitted, and transferees may not earn a profit on the transfer. This clearly reduces the incentives for entering into a transfer arrangement. On other projects, such as the Central Arizona Project, rules for transfers are unclear. However, for some proposed transfers, the Bureau of Reclamation has attempted to avoid burdening them with unreasonable restrictions or financial penalties.

market-oriented incentives, or a combination of both.

Before granting building permits, a number of political jurisdictions require the installation of water-saving devices or the demonstration of a secure water right. Several municipalities also have attempted to induce water conservation through pricing mechanisms and other methods, such as installing water-saving devices, metering, and repairing leaks (Martin et al. 1984; MWRA 1990). The Reclamation Reform Act of 1982 requires districts that receive water from federal projects to establish water conservation plans. However, this approach has several problems, including: (1) it has few teeth, unless an elaborate review process is set up; (2) it provides little basis for deciding which water conservation measures are appropriate; and (3) existing legislation provides no financial resources for implementing the water conservation measures.

The U.S. Bureau of Reclamation initiated several activities related to water conservation. These include:

• Establishing water conservation and advisory centers in the Bureau's regional and national offices. These centers coordinate water conservation programs, provide information on water supplies and conservation opportunities, provide technical assistance, training, and technology transfer, and promote public education programs.

Initiating investigations to develop integrated and comprehensive water conservation plans that will emphasize a more efficient use of water supplies. The United States has worked with water users and other entities to pursue opportunities to conserve water on existing projects through rehabilitation, structural modification, or operational changes. Completing a prototype project on the Coachella Canal in California to demonstrate techniques for lining canals while they remain full of water. This process allows water deliveries to continue while canals are lined to reduce seepage losses.

Water Conservation
Measures

Water conservation measures can play an important role in bringing supply and demand into balance. Water conservation can be induced by regulatory measures,

Flood Control

Changes in hydrology can increase or decrease flood threats on a regional basis. Many multiple-purpose water management projects and practices are designed to provide maximum flexibility to meet a wide range of changing demands. Employing floodplain management can yield additional flexibility in adapting to climate change.

Navigation

Climate change and natural variability could affect the navigability of the nation's waterways. Inland waterways tend to be more susceptible than coastal areas in cases of both increased and decreased river flows. Severe drought in 1988 closed many sections of the Mississippi River navigation system with significant disruption of commerce. The need to maintain navigation must be closely examined in order to determine the advisability of major investments in infrastructure (such as new locks, storage reservoirs, or channel dredging) to increase the flexibility of the system to function under a wider range of precipitation patterns. Several academic studies conducted as a result of the 1988 drought indicate that major investments have, at best, marginal economic efficiency with respect to the need to keep the systems open 100 percent of the time. Effects on coastal ports are unlikely to be significant because of the dampening effect of the ocean on river and estuary water levels and because of the long-term nature of potential sea level rise. Sufficient time appears to be available to alter coastal navigation infrastructure should significant sea level changes occur.

Desalinization Technologies

Desalinization technologies might prove useful in adapting to changes in climate if they can be economically justified. The United States has undertaken much research in this area. Significant programs carried out at the Yuma Desalting Test Facility in the 1970s and early 1980s included developing suitable pretreatment for the desalting units, testing proposed equipment, developing a program to test larger-scale equipment, and proof-testing desalting equipment. During construction, research and development focused on solving problems specific to the facility, including biomass and grit removal, chemical feed and piping failures, dual-media filter performance, and membrane degradation. The U.S. federal government has shared information on desalting problems, experiences, and solutions with the desalting industry through cooperative studies, sponsored tests, technical papers and presentations, and other technology-transfer forums.

In response to a congressional request, in 1990 the Bureau of Reclamation prepared A Plan for Improving Desalination and Water Treatment Technologies. This report provided a plan for establishing a cooperative program between the public and private sectors for developing desalination technologies (BOR 1992).

Drought Management

Many of the measures used to manage water under drought conditions will be useful if climate changes. The primary goal of most of these measures is to develop greater flexibility in existing management systems. One important innovation is the use of water banks, such as the banks in Idaho on the Boise and Payette River systems, and the California Emergency water bank. Users of the water banks may "deposit" their surplus water in the banks and make it available to others. The U.S. government has helped determine the quantities of water available for purchase, has reviewed the condition of ground-water wells, has approved transfers of base water-right supplies from federal service areas to other areas of need, and has helped coordinate joint federal and state project operations. In addition, on the Friant Unit of the Central Valley Project, water transfers occurred between districts as part of a surface-water and ground-water conjunctiveuse program. The U.S. government also provides monthly reports on drought conditions for water users and project operators to help them make timely decisions and to enhance public awareness. It also works with state drought-response programs to disseminate information on water supply and on programs for drought response.

System Optimization.

"System optimization" is the adoption of operational, management, institutional, or physical changes to gain more output from the same resources. “Joint use” is the coordinated use of federal facilities with nonfederal resources and management of a facility to optimize among multiple uses. Because of their cooperative natures, both approaches can meet new demands while maintaining services for existing users.

For example, in cooperation with the Western Area Power Administration, the Bureau of Reclamation developed a power optimization model to schedule hourly water releases from its dams in the Lower Basin of the Colorado River, in accordance with downstream water demands, physical and institutional constraints, and electrical loads. Also, at many of its projects, the Army Corps of Engineers manages water releases from its reservoirs to enhance downstream water quality, fish habitat, and recreational opportunities.

The government also developed an optimization scheme that could raise the efficiency of hydropower generation by 2 percent, producing more clean hydropower worth millions of dollars, without using additional water.