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Chapter 4. Rising Temperatures and Rising Seas: Reservoirs in the Sky
Snow/ice masses in mountains are nature’s freshwater reservoirs—nature’s way of storing water to feed rivers during the summer dry season. Now they are being threatened by the rise in temperature. Even a 1-degree rise in temperature in mountainous regions can markedly reduce the share of precipitation falling as snow and can boost that coming down as rain. This in turn increases flooding during the rainy season and reduces the snowmelt to feed rivers during the dry season.
In some agricultural regions, these “reservoirs in the sky” are the leading source of irrigation and drinking water. In the southwestern United States, for instance, the Colorado River—the primary source of irrigation water—depends on snowfields in the Rockies for much of its flow. California, in addition to depending heavily on the Colorado, also relies on snowmelt from the Sierra Nevada in the eastern part of the state. Both the Sierra Nevada and the coastal range supply irrigation water to California’s Central Valley, the world’s fruit and vegetable basket.
Preliminary results of an analysis of rising temperature effects on three major river systems in the western United States—the Columbia, the Sacramento, and the Colorado—indicate that the winter snow pack in the mountains feeding them will be dramatically reduced and that winter rainfall and flooding will increase accordingly. 27
With a business-as-usual energy policy, global climate models project a 70-percent reduction in the amount of snow pack for the western United States by mid-century. A detailed study of the Yakima River Valley, a vast fruit-growing region in Washington state, by the U.S. Department of Energy’s Pacific Northwest National Laboratory shows progressively heavier harvest losses as the snow pack shrinks, reducing irrigation water flows. A 2-degree-Celsius rise in temperature would reduce farm income in the valley by $92 million; a rise of 4 degrees Celsius would cut farm income by $163 million, nearly a quarter of the current harvest. 28
In Central Asia, the agriculture in several countries—Uzbekistan, Turkmenistan, Kyrgyzstan, Kazakhstan, Tajikistan, and Afghanistan—depends heavily on snowmelt from the Hindu Kush, Pamir, and Tien Shan mountain ranges for irrigation water. Nearby Iran gets much of its water from the snowmelt in the 5,700-meter Alborz Mountains between Tehran and the Caspian Sea. 29
Largest of all, where farmers are concerned, is the vast snow/ice mass in the Himalayas. Every major river in Asia, where half the world’s people live, originates in the Himalayas, including the Indus, the Ganges, the Mekong, the Yangtze, and the Yellow. If warmer temperatures increase rainfall and reduce snowfall in the Himalayas, there will be more flooding during the rainy season and less snowmelt to feed rivers during the dry season. 30
Reduced snow pack to feed the Yellow River flow will shrink China’s wheat harvest, the largest in the world. Alterations in the flow of the Yangtze River will directly affect China’s rice harvest—also the world’s largest. And India’s wheat harvest, second only to China’s, will be affected by the flows of both the Indus and the Ganges. Anything that lowers the summer flow of the Mekong will affect the rice harvest of Viet Nam, a leading exporter. 31
The shrinking of glaciers in the Himalayas could affect the water supply for hundreds of millions of people. In countries like India and China, the water stored during the rainy season as snow and ice for release in the dry season would be reduced or, in some cases, disappear entirely. The result would be more destructive floods alternating annually with more severe early summer water shortages. 32
There are many more mountain ranges where snow/ice regimes are shifting, including the Alps and the Andes. The snow/ice masses in the world’s leading mountain ranges and the water they store as ice and snow is taken for granted simply because it has been there since before agriculture began. Now that is changing. If we continue raising the earth’s temperature, we risk losing these reservoirs in the sky on which cities and farmers depend. 33
27. Krist, op. cit. note 13.
28. Michael J. Scott et al., “Climate Change and Adaptation in Irrigated Agriculture—A Case Study of the Yakima River,” in UCOWR/NIWR Conference, Water Allocation: Economics and the Environment (Carbondale, IL: Universities Council on Water Resources, 2004); Pacific Northwest National Laboratory, “Global Warming to Squeeze Western Mountains Dry by 2050,” press release (Richland, WA: 16 February 2004); Pacific Northwest National Laboratory, “We’re Here, We’re Warming, Can We Get Used to It?” press release (Richland, WA: 17 February 2005).
29. Bhawani S. Dongol et al., “Low Flows in the Middle Mountain Watersheds of the Hindu-Kush Himalayas (HKH),” paper presented at the International Conference on the Great Himalayas: Climate, Health, Ecology, Management and Conservation, Kathmandu, Nepal, January 2004; Mountain Agenda, Mountains of the World: Water Towers for the 21st Century (Bern: 1998); Mehrdad Khalili, “The Climate of Iran: North, South, Kavir (Desert), Mountains,” San’ate Hamlo Naql, March 1997, pp. 48–53.
30. For more information see Evelyne Yohe, “Sizing Up the Earth’s Glaciers,” NASA Earth Observatory, at earthobservatory.nasa.gov/Study/GLIMS, 22 June 2004.
31. Crop harvests from USDA, op. cit. note 3.
32. Robert Marquand, “Glaciers in the Himalayas Melting at Rapid Rate,” Christian Science Monitor, 5 November 1999.
33. Paul et al., op. cit. note 11; Lonnie G. Thompson, “Disappearing
Glaciers Evidence of a Rapidly Changing Earth,” American Association for the Advancement of Science Annual Meeting, San Francisco, CA, February 2001; Juan Forero, “As Andean Glaciers Shrink, Water Worries Grow,” New York Times, 24 November 2002; Monica Vargas, “Peru’s Snowy Peaks May Vanish as Planet Heats Up,” Reuters, 23 July 2004.
Copyright © 2006 Earth Policy Institute