The preceding sections have assessed the possible effects of climate change on the water resource base and on the demand for water, as well as the potential impacts on water users. Most published studies have looked at impacts in the absence of planned adaptation to climate change, and the few studies that have tried to cost impacts have had to make assumptions about adaptation. This section assesses opportunities in the water sector for adapting to climate change and explores any constraints which may exist.
Water management has always adapted to change (especially following extreme events or in response to increased demand), and climate change is just one of the pressures facing water managers. Other pressures include increasing demands for water resources or protection against hazard, changing water management objectives (which recently have included increasing recognition of the importance of meeting environmental needs as well as those of offstream demands), changing water management technologies, and altered legislative environments.
It is important to distinguish between development of adaptive options for meeting changing demands and resources and assessment of the abilities of a given water management agency (interpreted broadly) actually to adapt to climate change. Over the years, a wide range of adaptive techniques has been developed, largely in response to the need to meet increased demands. Broad distinctions can be drawn among supply-side adaptive techniques (changing structures, operating rules, and institutional arrangements) and demand-side techniques (which change the demand for water or protection against risk and include institutional changes as well). Examples of supply-side adaptations include increasing flood defenses, building weirs and locks to manage water levels for navigation, and modifying or extending infrastructure to collect and distribute water to consumers. Demand-side techniques include water demand management (such as encouraging water-efficient irrigation and water pricing initiatives), changing water allocations (Miller et al., 1997), and nonstructural flood management measures (such as land-use controls). Distinctions also can be drawn between anticipatory and reactive actions. The former are taken in advance of some change, the latter in response to a change. Reactive actions include short-term operational adaptations, such as temporary exploitation of new sources, and longer term measures. A major flood or drought, for example, often triggers a change in water management. However, although many adaptive options do exist, knowledge of these options and the expertise of officials to execute them may be limited in some situations.
The optimum extent of adaptation can be characterized in terms of the benefits and costs of adaptation. The extremes of adaptation are no adaptation and adaptation sufficient to eliminate all effects (which usually is not physically possible). The optimum level of adaptation minimizes the combined costs of adaptation and residual negative effects, with the most cost-effective steps taken first.
Water managers long have had access to many techniques for assessing options and implementing adaptive strategies. However, the techniques used have changed over time and vary between countries, and they are very much influenced by institutional arrangements in place in a country. Factors that affect adaptive capacity in a country include institutional capacity, wealth, management philosophy (particularly management attitudes toward supply-side versus demand-side strategies, as well as sustainable management), planning time scale, and organizational arrangements (adaptation will be harder, for example, when there are many different managers involved or where water managers do not have sound professional guidance).
This section looks first at water management options, then at management techniques. It contends that water managers generally are aware of technical and institutional optionsalthough for many reasons may not have access to all of themand that climate change challenges management techniques for assessing and selecting options, rather than the technical and institutional options themselves.
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