Significant loss of glaciers in Central Asia began around
Himalayas
the 1930s, and become more dramatic in the second half
of the 20th century and continue into the 21st century.
Glacier area was reduced by 25–30 per cent in the Tien
Shan, by 30–35 per cent in the Pamirs, including its larg-
est Fedchenko Glacier (Figure 6B.15), and by more than The ice extent in the Himalayas is estimated to be about
50 per cent in northern Afghanistan
39,113,115–117
. 33 050 square km
122
. Observations of individual glaciers in-
dicate annual retreat rates varying from basin to basin – in
Glaciers in higher altitudes (above 4 000 m above sea level) some instances showing a doubling in recent years com-
experienced less pronounced ice losses
39,113,119
. Total retreat pared to the early 1970s. An 8 per cent area loss was ob-
has reached several kilometres for many larger glaciers, served for glaciers in Bhutan between 1963 and 1993
123
. The
some hundred metres for smaller ones, and many hun- Imja Glacier in the Dudh-Koshi basin of the Everest region
dreds of small glaciers have vanished
39,113
. Glacier degra- retreated almost 1600 m between 1962 and 2001 and anoth-
dation is accompanied by increasing debris cover on many er 370 m by 2006 (Figure 6B.16). The Gangotri Glacier in
glacier termini and the formation of glacier lakes
39,113
. See Uttaranchal, India, retreated about 2 km between 1780 and
also the box on glaciers and water supply in Central Asia. 2001
124
. The glacier shrinking is accompanied by the forma-
tion of unstable glacial lakes that threaten downstream ar-
eas with outburst floods. For a discussion of the impacts of
Glaciers and water supply in Central Asia
glacier shrinking on water resources, please see the box on
On average, glacier melt contributes 10–20 per cent of the
the water towers of Asia, at the end of Part 1 of this chapter.
total river runoff in Central Asia
39,120
. 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 agricul-
ture – 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 vi-
tal role in sustaining agricultural production. Irrigated crops
such as cotton have survived, while most rain-fed crops, es-
pecially 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 situa- Figure 6B.16: Growth of Imja Tsho Lake, Himalayas. The lake start-
tion since many of the rivers are transboundary
121
. In Central ed to form in 1962 at the debris-covered tongue of Imja Glacier
Asia, the Amu Darya river basin, where input of glacier water and grew to an area of about 1 km
2
by 2006. The growing moraine-
is significant, and the densely populated Ferghana Valley, are dammed lake is potentially hazardous in case of a dam failure.
among most vulnerable to the impacts of droughts, climate Photo: Michael Hambrey, SwissEduc (www.swisseduc.ch)/Glaciers online
change and glacier degradation.
(www.glaciers-online.net); data from the International Centre for Integrat-
ed Mountain Development, Nepal
CHAPTER 6B GLACIERS AND ICE CAPS 139