actions either to deal with their effects or to prevent changes require concise information about the nature and timing of the effects at local, regional, and global levels" (Chen and Parry, 1987). The strategic few indices most important for figuring the impacts of climate change have not, however, been chosen, either for agencies to monitor or for scientists to predict. An analysis of likely effects of climate change suggests several indices about which detailed and long-term information would be especially useful.
The preeminent outdoor business, exposed to climate, is farming. Although frost kills many crops, species from sugarcane in the south to rape-seed in the north all grow food despite the range of temperatures. But they all need water, and they consume it in proportion to their growth (de Wit, 1958). Calculations show that warming would be hard on a crop grown on the northern margin of the Canadian Prairies unless it were balanced by more precipitation (Stewart, 1981). A steady water supply is the critical element for farming. The bare Mojave Desert and dripping Hoh River valley within one nation with an average precipitation of 750 mm (U.S. Geological Survey, 1984) make the point that global, even national, averages over large areas matter little. The water in a specific place matters.
The migration of Americans within the United States since 1960 shows they do not fear warmer climate (National Research Council, 1983). But they need water wherever they go, and their consumption of water in the Southwest now exceeds the average renewable supply (Gleick, 1990). Where the average supply matches demand, storage smooths the variation. The need for storage, however, depends on the variation across years and seasons (Rogers and Fiering, 1990). So, both average and steadiness of the supply of water are crucial for cities and suburbs as well as for farming.
Flow in streams integrates the effects of weather and landscape. The sensitivity of fish to stream flow is evident. Because different vegetation types are associated with particular seasonal patterns of stream flows, changes in flows signal impending vegetation changes. For example, deciduous forests thrive where soils are sufficiently wetted in the winter that trees can tap deep water and grow when the upper soil layers dry out in summer. Reduction in winter precipitation or reduced flows in summer would signal difficulties for that vegetation.
The sensitivity of industry to climate is exemplified by the generation of electricity. The use of water per unit of production by other industries has steadily declined (David, 1984). Water power obviously needs water, and thermoelectric plants are cooled by water, economically (Miller, 1990). So industry is affected by water supply.