EPIBuilding a Sustainable Future
Lester R. Brown

Chapter 4. Rising Temperatures and Rising Seas: Reservoirs in the Sky

Snow/ice masses in mountains are nature's freshwater reservoirs. These "reservoirs in the sky" are nature's way of storing water to feed rivers during the summer dry season. Agriculture is heavily dependent on these snow/ice masses, which are a major source of water for irrigated farming. Now they are being threatened by the rise in temperature.

In some agricultural regions, snowmelt is the leading source of irrigation water. These regions include the southwestern United States, where 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 the effects of rising temperature 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. John Krist, who writes for California's Ventura County Star, says that this "will mean less water flowing into reservoirs from snowmelt during dry months but more pouring in during flood-prone winter months when there is no room to store it." Many of the world's river irrigation systems are plagued with the same prospect.20

In Central Asia, the agriculture in several former Soviet republics depends heavily on snowmelt from the Hindu Kush mountain range. Among these are Uzbekistan, Turkmenistan, Kyrgyzstan, Kazakhstan, and Tajikistan. Afghanistan also depends on the Hindu Kush. Iran gets much of its water from the snowmelt in the 6,000-meter Elburz Mountains between Tehran and the Caspian Sea.

Largest of all in world food terms is the snow/ice mass in the Himalayas. Every major river in Asia originates in the Himalayas, including the Indus, the Ganges, the Mekong, the Yangtze, and the Yellow. If rainfall in the Himalayas increases and snowfall decreases, the seasonal flow of these rivers will change, leading to more flooding during the rainy season and less snowmelt to feed rivers during the dry season.21

This melting's impact on the Yellow River will affect 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, which is second only to China's, will be affected by the flows of both the Indus and the Ganges. Anything that alters the seasonal flow of the Mekong will reduce the rice harvest of Viet Nam, a leading source of rice for importing countries.22

There are many more mountain ranges where the snow/ice cover is melting, 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 has been taken for granted simply because it has always been there. Now that is changing. If we continue burning fossil fuels and raising the earth's temperature, we risk losing these reservoirs in the sky.

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20. John Krist, "Water Issues Will Dominate California's Agenda This Year," Environmental News Network, 21 February 2003.

21. For more information, see NASA Goddard Space Flight Center, "Decline of World's Glaciers Expected to Have Global Impacts Over This Century," press release (Greenbelt, MD: 29 May 2002).

22. Crop harvests from USDA, op. cit. note 8.


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