The rapid shrinking of Himalayan glaciers, which has accelerated at a considerable rate over the past decade, could have catastrophic consequences for communities living downstream and the millions who rely on glacial melt water, a new report says.
The extended Himalayan mountain range feeds nine perennial river systems in the region which constitute a lifeline for nearly 1.3 billion people downstream. Nearly 15,000 glaciers and 9,000 glacial lakes have been identified across five countries in the region - Bhutan, Nepal, Pakistan and selected basins of India and China. Of these, some 200 lakes have been identified as potentially dangerous.
Observations of individual glaciers indicate that, in some cases, rates of retreat have doubled since the early 1970s, though they vary from basin to basin. The Dudh Koshi is the largest sub-basin and most densely glaciated region in Nepal and contains 12 of the 20 potentially dangerous glacial lakes identified in the country. The glaciers in this basin are retreating at an average of 10 to 60 m annually; the Imja glacier by as much as 74 m a year. Melting glaciers are also leading to some of the fastest-growing glacial lakes in the region; the lakes form in the gap left between the retreating glacier terminus and the end moraine.
In Bhutan, the Luggye Glacier retreated by 160 m between 1988 and 1993 resulting in rapid growth of the lake Luggye Tso. The Raphstreng Glacier retreated 35 m per year on average between 1984 and 1988; the retreat rate almost doubled to 60 m per year between 1988 and 1993.
Glacial lake outburst floods can have varying degrees of socioeconomic impact. Their impact can be quite extensive since they can destroy villages, agricultural land, roads, bridges, hydropower plants, and trekking trails, as well as causing loss of life. 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 land, and caused considerable loss of life. The Luggye Tso GLOF in Bhutan in 1994 damaged the sacred Dzong and cultivated land, and also caused loss of life.
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 fresh water storage.
"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, dam breach, and hydrodynamic modelling are important for implementing mitigation measures to reduce risks to vulnerable mountain populations," said Surendra Shrestha, Regional Director of the UNEP Regional Office for Asia and the Pacific.
The report, The Impact of Climate Change on Himalayan Glaciers and Glacial Lakes, was produced by the International Centre for Integrated Mountain Development (ICIMOD) with the United Nations Environment Programme (UNEP) and launched during the World Environment Day regional celebrations held in Kathmandu, Nepal on 5 June 2007.
Environment Day, commemorated each year on 5 June 2007, is one of the principal
vehicles through which the United Nations stimulates worldwide awareness
of the environment and enhances political attention and action. The World
Environment Day slogan for 2007 is "Melting Ice - a Hot Topic?" In support
of International Polar Year, the WED theme selected for 2007 focuses on
the effects that climate change is having on polar ecosystems and communities,
and the ensuing consequences around the world.
This policy summary looks at reported and possible, future consequences of climate change in the greater Himalayan region. The main emphasis is on responses in high mountain cryogenic phenomena such as glaciers, permafrost, and avalanches; the implications for water supply, ecosystems, and hazards; and how these threaten regional populations. The assessment points to a serious need to improve relevant knowledge in the region concerning key policy areas and strategies to improve the adaptive capacities of communities at risk.
This, in itself, is signifi cant and has implications for regional water resources, as well as being an indicator of the scale of climate change. Some major hazards, from debris flows to glacial lake outburst floods (GLOFs), are becoming more frequent and severe (Beniston 2003). In fact, all aspects of the Himalayan cryosphere are affected by climate change. They include vast areas of permafrost and areas subject to snow avalanches or freeze-thaw and are affected by the changing balance between snow and rainfall. Complexities arise, especially from interactions among different cold climate elements.
The most rapid and varied interactions occur through the vertical 'cascade' of moisture and sediment between different topoclimates. Large and rapid downslope, down-glacier, or downstream cascades also exaggerate the scale and diffi culty of predicting hazards such as debris flows and flash floods. The varied ability of mountain species to respond as temperature warms, glaciers retreat, and weather extremes become more common threatens extinction for some and is a threat to biodiversity in general.
An important theme is the enormous diversity within the region in climates and topoclimates, hydrology and ecology, and, above all, in human cultures and the ways in which their activities are complexly interwoven with elements of the cryosphere and alpine ecosystem. The complex regional differentiation magnifi es the signifi cance of two major problems: the widespread absence of basic scientific investigations into cryogenic processes and limited knowledge of the human cultures and ongoing developments in them. This leads to the theme of 'uncertainty on a Himalayan scale', referring more to problems of limited knowledge than inherent physical and social uncertainties.
The impacts of climate change are not evenly distributed in intensity within the region, nor among different communities and sectors of society. However, the poorer, more marginalised, people of the high mountains are likely to suffer the earliest and the most. Given the evidence that many risks already threaten women disproportionately; and also the elderly, disabled, and indigenous groups, especially their poorer members; identifying changes in the cryosphere and alpine ecosystem most likely to affect them is of utmost importance. In addition, there are broader regional questions of which the more severe highland-to-lowland dangers relate to rapid melting events, floods caused by natural dam bursts, increased sedimentation, and droughts caused by reduced or changed flow patterns.
course, mountain people have lived with and survived great hazards for
thousands of years, but current rates of climate change are among the most
rapid known and they are superimposed on severe and, equally, uncertain
socioeconomic pressures. A range of issues and policy areas are identifi
ed, from the regional to local community levels, through which these problems
might be addressed. They involve land use, water management, disaster management,
energy consumption, and human health. It is argued that community-led adaptive
strategies and capacities, as well as substantial efforts to reverse the
human drivers of climate change, are needed. An important practical and
ethical requirement is for all levels of government, research, non-government
organisations, and professions to engage with mountain communities in combined
efforts to increase their adaptive capacities to climate change.
Intense rainfall is the most common cause of flash floods in the Himalayan region. These events may last from several minutes to several days. Such events may happen anywhere but are more common to mountain catchments. The main meteorological phenomenon causing intense rainfalls in the region are cloudbursts, stationarity of monsoon trough and monsoon depressions.
Landslide dam outburst
Debris from a landslide can temporarily block the flow of a river creating a reservoir in the upstream reach. The landslide dam can breach due to overtopping and cause huge floods known as landslide dam outburst floods (LDOF).
Glacial lake outburst
The glaciers in the Himalayas are mostly retreating, and as they retreat lakes can form from melt water held in by the now exposed terminal moraine acting as a dam. If the dam breaks the water can be released suddenly resulting in a glacial lake outburst flood.
Impact of climate change
Intense rainfall floods and landslide dam outburst floods are directly related to the hydrometeorological conditions and likely to be affected by climate change. Climate models project an increase in monsoon precipitation in the region. Similarly the frequency and magnitude of extreme rainfall events are also anticipated to. GLOFs are related to glacial retreat which in turn is mainly due to climatic warming. It is therefore very likely that flash floods due to intense rainfall, landslide dam outbursts, and glacial lake outbursts will increase in the future.
the region is highly exposed to flash flood hazards, due to poor socioeconomic
condition the vulnerability is also high. In general the capacity to manage
the risk of flash floods is low. ICIMOD has undertaken several initiatives
targeted towards mitigation of the impact of flash floods including development
of an inventory of glaciers and glacial lakes for a part of the Hindu Kush-Himalayan
region; an international workshop on flash floods in Lhasa, PR China; capacity
building for flash flood risk management; and satellite rainfall estimation.
ICIMOD will continue to work in flash flood management in the region particularly
in raising awareness towards flash floods, increasing capacity to manage
the risk, and linking flash floods risk management with climate change
The International Centre for Integrated Mountain Development (ICIMOD) is an independent 'Mountain Learning and Knowledge Centre' serving the eight countries of the Hindu Kush- Himalayas - Afghanistan , Bangladesh , Bhutan , China , India , Myanmar , Nepal , and Pakistan - and the global mountain community. Founded in 1983, ICIMOD is based in Kathmandu, Nepal, and brings together a partnership of regional member countries, partner institutions, and donors with a commitment for development action to secure a better future for the people and environment of the extended Himalayan region. ICIMOD's activities are supported by its core programme donors: the governments of Austria, Denmark, Germany, Netherlands, Norway, Switzerland, and its regional member countries, along with over thirty project co-financing donors. The primary objective of the Centre is to promote the development of an economically and environmentally sound mountain ecosystem and to improve the living standards of mountain populations.