Glaciers and water supply in Central Asia

On average, glacier melt contributes 10-20 per cent of the total river runoff in Central Asia39,120. During dry and hot years, the input of glacier water into summer river flow could be as high as 70-80 per cent, compared to 20-40 per cent in normal years. This proportion is critical for agriculture - the economic sector that consumes about 90 per cent of water resources and is highly dependent on water availability. During the severe droughts of 2000-2001 in the southern districts of Central Asia, glacier water played a vital role in sustaining agricultural production. Irrigated crops such as cotton have survived, while most rain-fed crops, especially cereals, failed. This has strongly affecting the food security of millions of people in Tajikistan, Afghanistan and Iran. It is expected that glacier recession in the long term could reduce water supply, affecting the agricultural sector and energy security, thereby destabilizing the political situation since many ofthe rivers are transboundary121. In Central Asia, the Amu Darya river basin, where input of glacier water is significant, and the densely populated Ferghana Valley, are among most vulnerable to the impacts of droughts, climate change and glacier degradation.

Figure 6B.16: Growth of Imja Tsho Lake, Himalayas. The lake started to form in 1962 at the debris-covered tongue of Imja Glacier and grewto an area of about 1 km2 by 2006. The growing moraine-dammed lake is potentially hazardous in case of a dam failure.

Photo: Michael Hambrey, SwissEduc (www.swisseduc.ch)/Glaciers online (www.glaciers-online.net); data from the International Centre for Integrated Mountain Development, Nepal

The ice extent in the Himalayas is estimated to be about 33 050 square km122. Observations of individual glaciers indicate annual retreat rates varying from basin to basin - in some instances showing a doubling in recent years compared to the early 1970s. An 8 per cent area loss was observed for glaciers in Bhutan between 1963 and 1993123. The Imja Glacier in the Dudh-Koshi basin of the Everest region retreated almost 1600 m between 1962 and 2001 and another 370 m by 2006 (Figure 6B.16). The Gangotri Glacier in Uttaranchal, India, retreated about 2 km between 1780 and 2001124. The glacier shrinking is accompanied by the formation of unstable glacial lakes that threaten downstream areas with outburst floods. For a discussion of the impacts of glacier shrinking on water resources, please see the box on the water towers of Asia, at the end of Part 1 of this chapter.

Figure 6B.16: Growth of Imja Tsho Lake, Himalayas. The lake started to form in 1962 at the debris-covered tongue of Imja Glacier and grewto an area of about 1 km2 by 2006. The growing moraine-dammed lake is potentially hazardous in case of a dam failure.

Photo: Michael Hambrey, SwissEduc (www.swisseduc.ch)/Glaciers online (www.glaciers-online.net); data from the International Centre for Integrated Mountain Development, Nepal

The Tibetan Plateau and surrounding regions in China have a total glacier area and volume of 59 400 km2 and 5600 km3, respectively. Glaciers in China have been retreating with an area loss of about 20 per cent since the Little Ice Age maximum extent in the 17th century125,126. Retreat increased during the last century, especially during the past ten years127,128. Several monitored glaciers show strong retreat. About 90 per cent of glaciers are retreating, and glacier retreat increases from the continental interior to the coastal margins127,128. With the impact of global warming on the region127,129,130, glacier shrinkage will be faster and pose a serious threat to water resources in this region (see box on the water towers of Asia, at the end of Part 1 of this chapter).

Glaciers in South America cover an area of about 25 700 square km131, mainly in the Patagonian Icefields, which represent 66 per cent of South America's total ice area132. Chile has by far most of the glaciers; Argentina has an important number of ice bodies all along the Andes; Venezuela has less than 2 km2 of ice at Pico Bolivar133. Less than 10 per cent of the glacier area is located in the tropical Andes134 (see box on tropical glaciers).

In southern Patagonia, the glacial advance appears to have peaked between the late 17th and early 19th centuries135. Medium and small glaciers in central Chile and Argentina have shrunk considerably. This will affect the future availability of water resources, as these glaciers can contribute up to 68 per cent of meltwater during dry seasons. (See box on glacier changes and water availability in the tropical Andes). Most of the calving glaciers in Patagonia have also experienced drastic retreat136, contributing significantly to sea level rise27,137. Ice avalanches in the cordillera have resulted in many thousands of deaths (see box on the deadly avalanches of Glaciar 511 in the Cordillera Blanca).

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