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FIG. 5.5.1 The hydrologic cycle. The large rectangle at the top represents the water in the atmosphere. The rectangles beneath represent the water in vegetation, in the soil reached by roots, in the aquifers below, and in open bodies of water. The rectangle for humanity represents the water in people and pipes. Arrows represent fluxes. Valves are placed on three fluxes to show their control by CO2. CO2 directly affects transpiration from foliage by enlarging it through faster photosynthesis and by narrowing leaf pores. Indirectly, CO2 warms the air temperature, speeding the evaporation from vegetation, soil, and open water. Faster evaporation decreases the water that runs off to bodies of water or into aquifers, increases pumping to irrigate soil, and even raises humanity's demands. The arrows from air down to vegetation, soil, and open water are the flux and addition to them by precipitation. Water resources are the pools signified by the rectangles for open water and aquifers. (Reprinted, with permission, from P.E. Waggoner and R.R. Revelle, 1990, Summary, Chap. 19 in Climate change and U.S. water resources, edited by P.E. Waggoner, New York: John Wiley and Sons.)

3. The global perspective presented in most studies is not specific enough to address the water resource implications in regional and local areas.

4. Global climate change might be controlled by effective programs to reduce the atmospheric emissions of greenhouse gases.

5. Global climate change must rise higher on national and international political agendas before effective societal measures can be implemented to control or manage the water resources implications.

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