Climate Change 2001:
Working Group II: Impacts, Adaptation and Vulnerability
Other reports in this collection Rocky Mountains-Southwest U.S. Subregion

Rapid population growth coupled with water supplies that are limited, heavily utilized, and highly variable present significant challenges to governments and the private sector in this region. The effects of climate change may add further stresses (Frederick and Schwarz, 1999). One strategy that has been developed to cope with these issues is use of water banks. Water banks can be used to mitigate the economic impacts of drought periods by increasing the reliability of water supply or by facilitating short-term reallocation of water among users. Water banks can be used for environmental purposes—for example, Idaho's water banks have provided significant quantities of water to assist anadromous fish passage (Miller, 2000b). However, to the extent that water banking entails increased water withdrawals from surface sources, there could be further adverse impacts on aquatic ecosystems.

There are two types of arrangements to which the term "water bank" has been applied. "Groundwater storage banks" include active conjunctive-use programs whereby surface water is used to recharge an aquifer, which is then used as a source of water supply during periods when surface water is less abundant. Another use of the term "water bank" refers to a formal mechanism created to facilitate voluntary changes in the use of water under existing rights. We can distinguish these as "water transfer banks." The defining feature of this type of water bank is that it provides an established process or procedure for accomplishing such transfers. California has pioneered the development of both types of water banks. Various groundwater recharge programs have been developed in California, some of which incorporate features of groundwater banks and water transfer banks. One such example, the Bakersfield Recharge Facility in Kern County, is discussed below. The Emergency Drought Water Banks set up by the state of California in 1991, 1992, and 1994 are examples of water transfer banks.

In 1987, at the beginning of a severe multi-year drought, California had relatively little experience with privately arranged water transfers outside the confines of individual irrigation districts and major project service areas. The lack of market development may have been related, in part, to the predominance of large state and federal water projects in California and, in part, to the difficulty of obtaining approval for such transfers from the California State Water Resources Control Board (SWRCB) (MacDonnell, 1990; NRC, 1992). As the drought persisted, it became clear that neither within-project water transfers nor those requiring approval of the SWRCB were likely to occur in sufficient volume to alleviate the very uneven impacts of the drought on major urban centers and irrigated agriculture. In 1991, the state responded to the growing crisis by creating the first Emergency Drought Water Bank. California's Department of Water Resources (DWR) acted as the manager of these water banks because most of the anticipated transfers required conveyance of the water through State Water Project (SWP) facilities (primarily the state's pumping plant in the Sacramento/ San Joaquin delta and the California aqueduct). DWR personnel negotiated the purchase contracts, monitored compliance with those contracts, obtained SWRCB approval where needed, and coordinated deliveries of water to purchasers. Despite initial difficulties in estimating the quantity of water needed and the appropriate price, as well as some concerns about uncompensated third-party impacts, the program generally is considered to have been a major success—with net economic benefits far exceeding any negative impacts (Howitt et al., 1992; Dixon et al., 1993; MacDonnell et al., 1994).

Another successful California water bank is the 1,135-ha recharge facility operated by the city of Bakersfield. This groundwater-banking program also facilitates water transfers. The city owns Kern River water rights, which yield a highly variable quantity of water from 1 year to the next. A portion of these rights is leased on long-term contracts to neighboring irrigation districts. The city has constructed a recharge facility into which it spreads much of its remaining Kern River water. This activity has increased the amount of water that potentially is available for extraction in the underlying aquifer. Three other water districts also are allowed to bank their surplus water by spreading it in the recharge facility. Each bank participant can withdraw the water in its own account, as needed (e.g., during drought periods), or transfer the water to another party:

"The banked water can be extracted and transported for direct use, sold or exchanged, with the stipulation that extracted water must be used in the San Joaquin Valley portion of Kern County for irrigation, light commercial and industrial, and municipal or domestic purposes, unless otherwise specified. Located upstream of the facility, the city of Bakersfield often sells its banked water to users downstream, or exchanges it for water from other sources" (Wong, 1999).

Operation of this recharge facility provides county water users with drought insurance and flood control benefits. "Banking recharge operations during flood release periods serve to minimize downstream flooding problems while maximizing recharge of water on the Kern River for local benefit" (Wong, 1999). For example, the bank participants successfully used the recharge facility in 1995 to manage heavy runoff. Prairies-Great Plains Subregion

An attempt at proactive "mitigation" of an atmospheric threat is the cloud seeding program underway in Alberta since 1996 to reduce the severity of hailstorms. Central North America is one of the most hail-prone regions in the world. A 1995 hailstorm did more than US$1.1 billion damage in Dallas, a 1990 storm did US$600 million damage in Denver, and a 1991 hailstorm did about US$240 million (CDN$340 million) damage in Calgary. Hailstorms account for more than half of the catastrophic events in this region. In the Alberta program, storms with the potential to generate hail damage are intensively treated through cloud seeding. Since the program began, there has been an increase in the number of potential hailstorms, yet a pronounced reduction in actual hail damage. Indeed, during the first 4 years of the program, only one storm has done damage in the area under supervision (IBC, 2000).

Throughout the long history of hail suppression in North America and elsewhere, success has been mixed (e.g., Changnon et al., 1978), so it is not yet clear whether this approach will work over the long term. The experimental program in Alberta is expected to continue indefinitely because the modest US$1 million (CDN$1.5 million) annual operating cost appears to be more than offset by the reduction in observed hail damage (IBC, 2000).

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