The Himalayan glaciers are the largest store of freshwater outside the polar ice caps. These glaciers supply 303 million cubic feet of water to many major rivers of the world like Indus, Ganges, Brahmaputra, Mekong, Thanlwin, Irrawady, Yangtze and Yellow Rivers, on which more than ten percent of humanity depend on their freshwater needs. However, thanks to global warming and increased human activity on the mountains, these glaciers are depleting at an alarming rate.
The data available with the World Wildlife Fund (WWF) indicates that about 67 percent of the nearly 12,124 square miles of Himalayan glaciers are retreating at the rate of about 10-15 meters (33-49ft) each year, and could vanish completely in another 50 years! The Gangotri glacier, the source of the Ganga, India’s holiest river, is retreating 75 feet a year, and the Khumbu Glacier in Nepal, where Edmund Hillary and Tenzing Norgay began their ascent of Everest, has lost more than three miles since the due first climbed the mountain in 1953.
INCREASE IN SEA LEVEL
The greatest danger posed by the depletion of any glacier is increase in sea level. The World Glacier Monitoring Service (WGMS) attribute 24 percent of the sea level rise in the world in the past 20 years to the depletion of the Himalayan glaciers.
One direct consequence of the sea level rise is that it puts the very existence of major costal cities at stake. In the Himalayan perspective, Karachi, Mumbai (Bombay), Kolkata (Calcutta) and even far away Kochi (Cochin) are in peril of being flooded out of existence even if the sea level rises by a few meters.
The rising sea level poses another danger. It increases pressure on the Earth’s crust, causing extreme geological disturbances such as earthquakes, tsunamis, and volcanic eruptions. Researches have established a direct correlation between erratic monsoons and depletion of glaciers.
In recent times, the western parts of the Indo-Gangetic plains suffer from severe droughts, each drought more intense and long lasting than the previous ones. Simultaneously, the eastern parts face high-intensity flooding. The draught of 1997-2002 was the most severe as well as the longest in parts of Pakistan. This was at the same time when parts of India, Nepal and Bangladesh suffered from devastating floods of unprecedented magnitude.
REDUCTION OF WATER AVAILABILITY
In the short run, depletion or retreat of the glacier means more water for the glacier-dependent perennial rivers. However, this will be short-lived, and in any case pose a threat to the existing dams and reservoirs in the region. More melting means higher silt loads that reduce the life of dams and reservoirs.
Another danger of the high water flow is flooding that can severely affect paddy crop, the major crop cultivated in the Indo-Ganges plain. Although paddy is a water-loving plant, long-standing flood waters ruin the plant’s metabolism and adversely affect its growth.
In the long run, depletion of the glacier would mean reduction of the water flow, posing serious eco-environmental problems. In the Indian Himalayas, this has already happened, and signs of water shortages are evident everywhere. Many wells have already dried up and with each passing year, people feel the reduced availability of water for agriculture. Remote sensing satellites of India’s Space and Research Organization have found a 23 percent drop in glacial water in nineteen of the thirty glaciers mapped in the region.
GLACIAL LAKE OUTBURSTS
Another threat caused by the retreat of the glaciers is Glacial Lake Outburst. High altitude lakes are formed when the glacier’s terminal moraine retain some of the ice melt. When the volume of water becomes too great for the moraine to support or when events like melting of ice cores and rock/ice avalanches occur, these moraines fail and the water burst out. Such outbursts are unpredictable and very damaging. In the upper Indus River system, Thirty-five such destructive outbursts occurred in the past 200 years, with the frequency increasing in the recent past.