"It's the best summation of humanity's converging ecological problems and the best roadmap to sovling them, all in one compact package." —David Roberts, Grist on Plan B 4.0: Mobilizing to Save Civilization.
Chapter 2. Emerging Water Shortages: Rivers Running Dry
As the world's demand for water has tripled over the last half-century and as the demand for hydroelectric power has grown even faster, dams and diversions of river water have drained many rivers dry. As water tables have fallen, the springs that feed rivers have gone dry, leading to the disappearance of some rivers.
As noted earlier, the Colorado, the major river in the southwestern United States, now rarely makes it to the sea. With the states of Colorado, Utah, Arizona, Nevada, and, most important, California, depending heavily on the Colorado's water, the river is simply drained dry before it reaches the Gulf of California. This excessive demand for water destroys the river's ecosystem, including, of course, its fisheries.30
Dams on rivers are built for irrigation, to generate electricity, and to supply water to cities and industry. Since 1950, the number of large dams, those over 15 meters high, has increased from 5,000 to 40,000. Each dam deprives a river of some of its flow. Engineers like to say that dams built to generate electricity do not take water from the river, only its energy, but this is not entirely true since reservoirs increase evaporation. The annual loss of water in arid or semiarid regions, where evaporation rates are high, is typically equal to 10 percent of the reservoir's storage capacity.31
The loss of river flow can affect the health of estuaries and of inland lakes and seas. The Helmand River, which originates in the mountains of eastern Afghanistan, flows westward across the country and into Iran, where it empties into Lake Hamoun. When the Taliban built a new dam on the Helmand during the late 1990s, in violation of a water-sharing agreement between the two countries, they effectively removed all the remaining water. As a result, Lake Hamoun, which once covered 4,000 square kilometers, is now a dry lakebed. The abandoned fishing villages on its shores are being covered by sand dunes coming from the lakebed itself.32
A similar situation exists with the Aral Sea. The Amu Darya—which, along with the Syr Darya, feeds the Aral Sea—is now drained dry by Uzbek and Turkmen cotton farmers upstream. With the flow of the Amu Darya now cut off, only the diminished flow of the Syr Darya keeps the Aral Sea from disappearing entirely.33
Over the last few decades, the Aral Sea has shrunk some 58 percent in area and has lost 83 percent of its volume of water. The loss of freshwater recharge and the sea's shrinkage have led to a dramatic rise in salt levels and the demise of its rich fisheries. In addition to sandstorms, the region also now suffers from salt storms, which arise from the exposed seabed.34
China's Yellow River, which flows some 4,000 kilometers through five provinces before it reaches the Yellow Sea, has been under mounting pressure for several decades. It first ran dry in 1972, and since 1985 it has failed to reach the sea for part of almost every year.35
The Nile, the site of another ancient civilization, now barely makes it to the sea. Sandra Postel, in Pillar of Sand, notes that before the Aswan Dam was built some 32 billion cubic meters of water reached the Mediterranean each year. After the dam was built, however, and irrigation and other demands on the river increased, the Nile's discharge declined to less than 2 billion cubic meters.36
Pakistan, like Egypt, is essentially a river-based civilization. The Indus not only provides surface water, it also recharges aquifers that supply the thousands of irrigation wells that now dot the Pakistani countryside. But it, too, is starting to run dry in its lower reaches.37
In Southeast Asia, the flow of the Mekong is being reduced by the dams being built on its upper reaches by the Chinese. The downstream countries, including Cambodia, Laos, Thailand, and Viet Nam—countries with 160 million people—complain about the reduced flow of the Mekong, but this has done little to curb China's efforts to exploit the power and the water in the river.38
A similar situation exists with the Tigris and Euphrates rivers, which originate in Turkey and flow into Syria and Iraq en route to the Persian Gulf. This river system, the site of Sumer and other early civilizations, is being used at near capacity. Large dams erected in Turkey and Iraq have reduced water flow to the once "fertile crescent," helping to destroy more than 90 percent of the formerly vast wetlands that enriched the delta region.39
Many of the river systems just discussed are described by hydrologists as "closed basins"—that is, virtually all the water in the basin is being used. If one party gets more water, other parties will get less. In most cases, this means that as urban and industrial needs rise, there is less available for irrigation.
30. Postel, op. cit. note 3, pp. 261-62; Jim Carrier, "The Colorado: A River Drained Dry," National Geographic, June 1991, pp. 4-32.
31. Sandra Postel, Last Oasis (New York: W.W. Norton & Company, 1997), pp. 38-39.
32. UNEP, op. cit. note 3, pp. 50-59.
33. Ibid, p. 60.
35. Lester R. Brown and Brian Halweil, "China's Water Shortages Could Shake World Food Security," World Watch, July/August 1998, p. 11.
36. Postel, op. cit. note 3, pp. 71, 146.
37. Ibid., pp. 56-58.
38. Meinzen-Dick and Rosegrant, op. cit. note 26.
39. UNEP, "'Garden of Eden' in Southern Iraq Likely to Disappear Completely in Five Years Unless Urgent Action Taken," news release (Nairobi: 22 March 2003); Hassan Partow, The Mesopotamian Marshlands: Demise of an Ecosystem, Early Warning and Assessment Technical Report (Nairobi: Division of Early Warning and Assessment, UNEP, 2001).
Copyright © 2003 Earth Policy Institute