A slow retreat20 May 2011
Although slower than previously anticipated, climate change is still affecting the retreat of glaciers in the Himalayan region. The effects of this on the future availability of water resources, plus the immediate risk from glacier lake flooding, have been examined in a new report
High Asia is dominated by many steep, dramatic mountain ranges that run through parts of Nepal, Bhutan, Afghanistan, India, China, Tajikistan, Kyrgyzstan and other countries. The region is home to more than 50,000 glaciers that are vital water lifelines to Asia’s largest rivers. These include the Yellow, Yangtze, Mekong, Indus and Ganges. Roughly 2B people depend on these rivers for their water and food supply.
Although the massive glaciers of the greater Himalayan region are retreating more slowly than previously thought, development agencies are being urged to take steps now to help the region’s communities prepare for the many ways glacier melt is expected to impact their lives. This was the focus of a new report entitled Changing Glaciers and Hydrology in Asia: Addressing Vulnerability to Glacier Melt Impacts. Prepared in late 2010, it was a collaboration between Battelle, which operates the US Department of Energy’s Pacific Northwest National Laboratory, and the US Agency for International Development.
“The extremely high altitudes and sheer mass of High Asian glaciers mean they couldn’t possibly melt in the next few decades,” said Elizabeth Malone, a senior research scientist at Battelle and the report’s technical lead. “But climate change is still happening and we do need to prepare for it. That’s especially true in this part of the world, where poverty and other concerns make its residents very vulnerable to any change.”
Glaciers can be thought of as ‘time machines’ as they store water in one place over many decades. The report states that there is an inadequate amount of scientific data and knowledge about addressing glacier-related issues. Little attention has been paid to the downstream implications of glacier melt and adaption strategies, while retreating glaciers can also heighten existing water worries. A certain amount of runoff is provided by glaciers to downstream communities in China, India and the southeast Asia mainland. In the eastern Himalayas the contribution of melting glacier ice to the downstream river flow is less than 5%. However in the west and the Indus basin this is considerably more. Approximately 30% or more of flow of the Indus River is provided by glacier melt water, with snow and ice perhaps providing over two-thirds. As such the Indus River has the largest ratio of melt water to population of any river system anywhere in the world.
However, the report cautioned, realistic, accurate and comprehensive assessments of the future availability of water resources in High Asia and the downstream areas in the context of glacier retreat are not possible until: the existing hydrologic regime of the High Asian mountains is defined more clearly; the current relationship between glaciers and stream flow is evaluated; and the contribution from other sources of stream flow is examined.
Glacier ice melt rate under any reasonable future global warming scenario is relatively slow. A common misconception is the concern that the rapid melting of glaciers will lead to catastrophic flooding downstream. This is physically impossible, the report states. The real environmental hazards come in the form of two distinct glacier lake outburst floods (GLOFs).
1) A moraine-dammed outburst flood occurs when large volumes of water build up behind the terminal moraine of a rapidly melting, retreating glacier and the moraine dam fails. In 1985 a glacier lake at Dig Tsho in Nepal burst and the flood water completely destroyed a hydropower station at Thame 12km below. While considered to be one of the most dangerous moraine-dammed glacier lakes in the Himalayas, Imja Glacier lies south of Mount Everest. However the results of a 20-year study now show that it is relatively stable.
2) The second type of outburst flood is associated with advancing glaciers. This occurs when the glacier tongue dams a river. An outburst flood may occur when the glacier retreats or breaks up. In the Karakoram region there is a greater amount of such ice-dammed lakes formed by advancing glaciers in contrast to moraine-dammed lakes. Regions where advancing glaciers may soon impound rivers are the Shaksgam, upper Shyok and Shimshal valleys.
GLOFs are one of the most pressing near-term impacts of glacier melt. Those most affected by the floods are residents of rural villages close to glaciers. Although the number of people directly impacted can be small, the damage can often be extensive. The people who survive must move and begin to rebuild their lives in other places. Most GLOFs have been recorded in Bhutan, Nepal and Tibet since the 1930s and it is likely that more will occur as climate change progresses.
Glacier melt can potentially impact all sectors of economic growth, governance and health. The report highlighted the complexity surrounding the issue in the region and the critical need to prepare today for future environmental changes. Practical, cross-sectoral approaches to addressing glacier retreat in Asia were examined which, if implemented well, can produce multiple benefits.
“Glaciers may not be disappearing as fast as had been previously thought,” Malone says, “but climate change is happening in the Himalayas and having an effect. If systems – both human and ecological – are already stressed they are less able to be resilient in the face of change. But the good new is that we can take actions now that will be crucially important to how societies respond in the future.”
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