Our analysis of the global water situation, as well as regional case studies such as those presented here, reveals the following general conclusions:
The critical water issues of the next few decades will be regional and basin-scale rather than global. However, regional issues will have global impacts through their collective effects on world trade, political conflict, and incentives for technological innovation.
The most serious problems of water scarcity will be associated with irrigated agriculture in developing countries where subsistence farming accounts for most of the local food supply. Although it may eventually be desirable for such regions to cut back on irrigated agriculture and import more food from more humid regions, this will require substantial changes in their economies. Domestic and industrial needs are a small fraction of agricultural water use and can be reduced even further with existing technology and proven conservation practices. While irrigated agriculture can certainly benefit from efficiency improvements, it is unlikely that these improvements will keep pace with increasing demands for food.
Water quality problems associated with fertilizer and pesticide application will remain serious in some regions, but will probably diminish in others as agricultural practices and products become more environmentally sensitive. The technology to reduce discharges of potentially harmful agricultural chemicals is already available and will continue to improve.
The more serious problem will be allocation of the costs of using this technology.
Salinization is likely to become the dominant agricultural water quality problem in much of the world. In some cases, the direct and external costs of salinization will be too high to justify continuation of irrigated agriculture. In others, existing crops will have to be replaced by substitutes which are more salt tolerant or which are more amenable to salinity control.
Stresses imposed by unsustainable depletion or by degraded water quality may take effect gradually, over many years. In some areas, farmers may adapt to changing environmental conditions by changing crops, by accepting lower yields (and incomes), or by adopting new cultivation practices and technologies. Other parties, such as downstream users, may also adapt in various ways to water shortages and degraded water quality. In all of these cases, explicit and/or hidden costs can be expected to be incurred.
There is a real need for more reliable and scientifically defensible assessments of regional water issues and of the prospects for the future. Uncertainties in the magnitude and quality of water fluxes, stocks and demands at the regional level frequently lead to differing opinions about the nature, severity and cause of water problems. This can, in turn, lead to the adoption of inappropriate or counterproductive policies. Scientists, engineers and economists can all play a role in making the policy process better informed and more effective. This will help to insure that we can provide secure food supplies for an increasing population while protecting our water resources.
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