Both supply of and demand for water resources are likely to change in a warming climate. As population increases and urbanization proceeds apace, there is also likely to be greater demand for water from competing domestic and commercial users. Studies show that increased water requirements for agriculture in many regions are likely under warming conditions, and that there is potential for decadal "surprises" in the reliability and percentage of water demand that can be met (Figure 10.7a) (Strzepek et al., 1999; Doll, 2002).
Research on water resources for agriculture in temperate areas has shown that changes in seasonality such as earlier snowmelt will likely change the filling and use of reservoirs and hence of water availability for irrigation (Figure 10.7b) (Strzepek et al., 1999). Current utilization plans for such facilities will need to be adjusted and readjusted as the decades proceed. Whereas early work on climate change impacts on agriculture tended to focus on the effects of more frequent droughts, recent work has emphasized the important role of damage from floods and excess soil moisture as well (Figure 10.7c) (Rosenzweig et al., 2002). Early decades in the century may tend to be wetter and the later ones drier, due to the greater effect of rising temperatures on evaporative demand later in the century.
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