Issues in Ecology
Life on earth depends on the continuous flow of materials through the air, water, soil, and food webs of the biosphere. The movement of water through the hydrological cycle comprises the largest of these flows, delivering an estimated I 10,000 cubic kilometers (km^> of water to the land each year as snow and rainfall. Solar energy drives the hydrological cycle, vaporizing water from the surface of oceans, lakes, and rivers as well as from soils and plants (evapotranspiration). Water vapor rises into the atmosphere where it cools, condenses, and eventually rains down anew. This renewable freshwater supply sustains life on the land, in estuaries, and in the freshwater ecosystems of the earth.
© 2001 The Ecological Society of America
Jackson, R. B., Carpenter S. R., Dahm C. N., McKnight D. M., Naiman R. J., Postel S. L., and Running S. W. (Spring 2001). Water in a Changing World. Issues in Ecology, 9, 1-16.