is where it's at.
of a hothouse world
What will global warming do to the supply of fresh water? As the ocean warms, sea level will rise. We'll see more evaporation and precipitation, and more storms. While the local effects of global warming cannot be predicted, "You can't not look at it," says Sandra Postel. Warming "will literally change the hydrology of every major river basin in the world, especially in Asia."
While regional rainfall is hard to predict, increases in temperature will affect the snow supply that feeds major rivers. "Most major rivers in Asia come from the mountains," Postel notes. "The Ganges, Indus, and Yellow are dependent on mountain snowpack for their flow." Snowpack, she says, is "beautiful from a water point of view" because the snow is a natural reservoir that melts in spring and summer, just when water is needed in downstream areas.
As temperatures warm, she says, more precipitation will fall as rain, and the snow will melt sooner, so peak runoff will occur earlier in the year. The change, Postel says, "will worsen the water situation in places where they are already scrambling." She cautions that the Ganges, Indus and Yellow are already "tapped out in the dry season." The same problem could affect rivers fed by the Andes, Rockies, and Alps.
Overall, the problem is an unending demand, caused by soaring population and industrialization, splashing up against a finite supply. The water crisis is "definitely getting worse," says Postel. "The basic issue is the fact that water is renewable but finite, any place where the population grows, you'll have a diminished supply per person."
Rather than continually looking for another river to dam, Postel suggests working more intelligently with the existing supply. "We need a fundamental shift to meeting basic human needs and improving efficiency rather than continuing to find new sources. That's a no-win proposition. Every additional unit we take out of the natural environment causes environmental degradation. We need to do more with less through a focus on policy and institutions."
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