3.6.2 Adaptation options in principle

The TAR drew a distinction between ‘supply-side’ and ‘demand-side’ adaptation options, which are applicable to a range of systems. Table 3.5 summarises some adaptation options for water resources, designed to ensure supplies during average and drought conditions.

Each option, whether supply-side or demand-side, has a range of advantages and disadvantages, and the relative benefits of different options depend on local circumstances. In general terms, however, supply-side options, involving increases in storage capacity or abstraction from water courses, tend to have adverse environmental consequences (which can in many cases be alleviated). Conversely, the practical effectiveness of some demand-side measures is uncertain, because they often depend on the cumulative actions of individuals. There is also a link between measures to adapt water resources and policies to reduce energy use. Some adaptation options, such as desalination or measures which involve pumping large volumes of water, use large amounts of energy and may be inconsistent with mitigation policy. Decreasing water demand in a country by importing virtual water (Allan, 1998; Oki et al., 2003b), in particular in the form of agricultural products, may be an adaptation option only under certain economic and social conditions (e.g., financial means to pay for imports, alternative income possibilities for farmers).

These do not exhaust the range of possibilities. Information, including basic geophysical, hydrometeorological, and environmental data as well as information about social, cultural and economic values and ecosystem needs, is also critically important for effective adaptation. Programmes to collect these data, and use them for effective monitoring and early warning systems, would constitute an important first step for adaptation.

In the western USA, water-market transactions and other negotiated transfers of water from agricultural to urban or environmental uses are increasingly being used to accommodate long-term changes in demand (e.g., due to population growth) as well as short-term needs arising from drought emergencies (Miller, 2000; Loomis et al., 2003; Brookshire et al., 2004; Colby et al., 2004). Water markets have also developed in Chile (Bauer, 2004), Australia (Bjornlund, 2004), and parts of Canada (Horbulyk, 2006), and some types of informal and often unregulated water marketing occur in the Middle East, southern Asia and North Africa (Faruqui et al., 2001). Countries and sub-national jurisdictions differ considerably in the extent to which their laws, administrative procedures, and documentation of water rights facilitate market-based water transfers, while protecting other water users and environmental values (Miller, 2000; Faruqui et al., 2001; Bauer, 2004; Matthews, 2004; Howe, 2005). Where feasible, short-term transfers can provide flexibility and increased security for highly valued water uses such as urban supply, and in some circumstances may prove more beneficial than constructing additional storage reservoirs (Goodman, 2000).

Some major urban water utilities are already incorporating various water-market arrangements in their strategic planning for coping with potential effects of climate change. This is true for the Metropolitan Water District of Southern California (Metropolitan), which supplies wholesale water to urban water utilities in Los Angeles, Orange, San Diego, Riverside, San Bernardino, and Ventura counties. Metropolitan recently concluded a 35-year option contract with Palo Verde Irrigation District. Under the arrangement, the district’s landowners have agreed not to irrigate up to 29% of the valley’s farm land at Metropolitan’s request, thereby creating a water supply of up to 137 Mm³ for Metropolitan. In exchange, landowners receive a one-time payment per hectare allocated, and additional annual payments for each hectare not irrigated under the programme in that year. The contract also provides funding for community improvement programmes (Miller and Yates, 2006).

Options to counteract an increasing risk of floods can be divided into two categories: either modify the floodwater, for example, via a water conveyance system; or modify the system’s susceptibility to flood damage. In recent years, flood management policy in many countries has shifted from protection towards enhancing society’s ability to live with floods (Kundzewicz and Takeuchi, 1999). This may include implementing protection measures, but as part of a package including measures such as enhanced flood forecasting and warning, regulations, zoning, insurance, and relocation. Each measure has advantages and disadvantages, and the choice is site-specific: there is no single one-fits-all measure (Kundzewicz et al., 2002).