RAOnline Bhutan: Retreating Glaciers - Fast Melting Glaciers from Rising Temperatures Expose Millions in Himalaya to Devastating Floods and Water Shortages

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Glacial Lakes from Retreating Glaciers

Fast Melting Glaciers from Rising Temperatures Expose Millions in Himalaya to Devastating Floods and Water Shortages

The rapid shrinking of Himalayan glaciers, accelerating at alarming rates in past decades as a result of global warming, will have catastrophic consequences for communities living downstream and millions who rely on glacial melt water, a new report says.

The report, the first comprehensive study on the impact of warming temperatures on glaciers and glacial lakes in the Himalayan region warns of impending glacial lake outburst floods (GLOFs) - when rising waters from glacial melt breach dams in glacial lakes - and calls for early warning and mitigation measures to avert disaster.Nearly 15000 glaciers and 9000 glacial lakes are found in the Himalayan mountain chain which stretches 2500 km across five countries - Bhutan, Nepal, Pakistan, India and China.

The mountain range feeds nine perennial river systems in the region and constitutes a lifeline for nearly 1.3 billion people downstream.

Himalayan glaciers are shrinking at an average of 10 to 60 m annually, with some retreating by 74 m a year. In China, glaciers have been retreating at a rate of 5.5 per cent in the last three decades. With current climate change projections two-thirds of China's glaciers are likely to disappear by 2050, and almost all would be gone by 2100.

Significant changes were also seen in the Indian Himalaya, with the highest rate of glacial retreat found in the Bada Shigri Glacier and lowest in the Chhota Shigri Glacier in the Chenab River Basin, where glaciers are retreating by 6.8 to 29.8 m each year.

In Bhutan, the Luggye Glacier retreated by 160 m yearly from 1988 to 1993 resulting in rapid growth of the Luggye Tso Lake. The Raphstreng Glacier retreated 35 m every year on average from 1984 to 1998 but from 1988 to 1993 the retreat rate almost doubled to 60 m per year.

Glacier retreat has been accelerating in Nepal since the 1990s, with dramatic retreats recorded between 1994 and 1998 especially in the Dudh Koshi sub-basin where all of the glaciers studied have retreat by 10 to 59 m yearly. The Dudh Koshi sub-basin is the largest basin and most densely glaciated region in Nepal.

Melting glaciers are also leading to some of the fastest-growing glacial lakes in the region. Some glacial lakes have grown by almost 800 per cent since the 1970s.

Glacial Lakes From Melting and Receding Glaciers
This composite image from the ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer) instrument aboard NASA's Terra satellite shows how the Gangotri Glacier (India) terminus has retracted since 1780. Glacial lakes have been rapidly forming on the surfaces of debris-covered glaciers worldwide during the last few decades.
IMAGE COURTESY: Jeffrey Kargel, USGS / NASA JPL / AGU

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NASA ASTER

Nepal and Bhutan have the highest concentration of glacial lakes with 20 potentially dangerous lakes in Nepal and 24 in Bhutan. Of this, Lake Imja Tso in the Dudh Koshi Basin in Nepal, home to Mount Everest and one of the most popular tourist destinations and trekking route is among the most hazardous.

"Communities and businesses are still reeling from the devastating 1985 Dig Sho GLOF which is also found in the same basin. We anticipate that the impact of a GLOF in Imja Sho will be six times greater, and will extract a heavy toll on heavily populated settlements downstream, not to mention the devastation it would bring to infrastructure and agricultural lands. There will be a high human and economic cost," said Surendra Shrestha, Regional Director of the UNEP Regional Office for Asia and the Pacific.

Glacial floods are a regular occurrence in the Himalaya region with varying degrees of socio-economic impact. Their impact can be quite extensive since they destroy villages, agricultural lands, roads, bridges, hydropower, trekking trails as well human lives and property. The Tibetan Zhangzhangbo GLOF in 1981 caused extensive infrastructural damage and nearly US$3 million in losses. The Dig Tsho GLOF in Nepal in 1985 destroyed a power plant (with a loss of US$1.3 million), destroyed homes and lands and many losses of lives. The Luggye Tso GLOF in Bhutan in 1994 damaged sacred areas, cultivated land and lives.

The Hindu Kush-Himalaya glaciers are also an important source of freshwater for hundreds of millions of people living downstream. Glacial retreat is also causing long term loss of natural water storage of fresh water.

"The significance of these glaciers to downstream communities is of particular importance. Changes in glacier ice or snowmelt affects water yield to downstream regions heightening the risk of water shortages, impacts irrigation water for crops and may disrupt industry and power generation," said Dr. Andreas Schild, Director General of the International Centre for Integrated Mountain Development.

"We have to continue monitoring glaciers and glacial lakes to ensure sound management of these valuable water resources. In addition, the use of early warning systems like satellite-based techniques and mitigation measures such as dam breach and hydrodynamic modeling are important to reduce risks to vulnerable mountain populations," Shrestha added.

Source: United Nations Environment Programme UNEP June 2007