Most glaciers in South Asia’s Hindu Kush Himalayan region are retreating, but the consequences for the region’s water supply are unclear, a new report from the National Research Council finds. The report examines how changes to glaciers in South Asia’s Hindu Kush Himalayan region could affect the amount of water flowing in the area’s river systems, water supplies, and the South Asian Population. This image shows Mt. Taboche in the Khumbu Valley, Nepal. Image source: Alton Byers, Khumbu, Nepal, The Mountain Institute, http://commons.wikimedia.org/wiki/File:Icimod4_3520794097.jpg
Extending over 2,000 km across South Asia, the Hindu Kush Himalayan region includes all or parts of Afghanistan, Bangladesh, Bhutan, China, India, Nepal, and Pakistan.
The region is the source of many of Asia’s major rivers, including the Indus, Ganges, and Brahmaputra Rivers, which provide water for drinking and irrigation for about 1.5 billion people. Image source: Fotopedia/Jesús Tejel
The region is also home to some of the world’s most spectacular glaciers, which play an important role in the region’s hydrology. The meltwater generated from these glaciers each summer supplements the rivers and streams of the region. This image shows the Naimona'nyi glacier in southwestern Tibet. Image source: Thomas Nash, Smithsonian
Glaciers in the eastern and central regions of the Himalayas are retreating at rates that have accelerated over the past century. This has prompted concerns that, over time, the glaciers of the Hindu Kush Himalayas will dwindle in size until normal glacier melt can no longer contribute to the region’s water supply. This image shows the position of the end (terminus) of Gangotri Glacier, India, between 1780 and 2001. Image Source: U.S. Geological Survey. Glacier retreat boundaries courtesy of the U.S. Land Processes Distributed Active Archive Center. http://gallery.usgs.gov/photos/08_25_2010_s85Are1QPl_08_25_2010_4#.UE9ZR1GByVt
Although most glaciers are retreating, some glaciers in the western Himalayas are more stable and may even be increasing in size. The entire Himalayan climate is changing, the region is vast and so varied in climate, precipitation, and in glacial behavior and dynamics that it remains challenging to determine exactly how retreating glaciers will affect water supply in each location.
Due to factors including the remoteness and political instability of some parts of the Hindu Kush Himalayas, hydrological field data from the region is sparse. Here, researchers trek across the Guliya ice cap on the Tibetan Plateau after a snowstorm. Image source: Lonnie Thompson, The Ohio State University
Data that show how glaciers responded to previous shifts in climate are also limited. There are five ice core records for the Hindu Kush Himalayan region (in red), which extend back more than 2000 years. Because the climate of the region is varied, more ice core data is needed to form a complete picture of the region’s paleoclimate.
Recent studies show that at lower elevations, glacial retreat is unlikely to cause significant changes in water availability over the next several decades. These areas depend primarily on water from monsoonal rains and less on glacial meltwater. Therefore, factors such as groundwater depletion and increasing human water use could have a greater impact on water supply than glacial retreat.
Higher elevation areas could experience altered water flow in some river basins if current rates of glacial retreat continue, but shifts in the location, intensity, and variability of rain and snow due to climate change will likely have a greater impact on regional water supplies.
Glacial meltwater can act as a buffer against the hydrologic impacts of a changing climate, such as more frequent droughts. Although retreating glaciers would provide more meltwater in the shorter term as glaciers shrink, the loss of glacier “insurance” could become problematic over the longer term. This image shows glacier lakes feeding into rivers and streams. Image source: Daniel Miller, USAID
Social changes are likely to have at least as much of an impact on water demand as environmental factors do on water supply. Although some areas are sparsely inhabited, the Hindu Kush Himalayan region contains some of Earth’s most densely populated areas, and many river basins are already water stressed. Water stress could intensify if populations continue to increase over the next several decades.
It’s predicted that the region will become increasingly urbanized in coming years as people migrate to cities in search of economic opportunities. As living standards in cities rise, water use will likely increase— for example, if more people eat diets rich in meat, more water will be needed for agricultural use. Climate change could further exacerbate this water stress.
Most water use in the Hindu Kush Himalayan region is for agricultural irrigation. As the region’s population increases, pressure is growing to farm land more intensively in order to produce enough food. In India, this has led to a shift away from relying on water delivered through canals and irrigation systems for agricultural use. Instead, farmers compete to extract groundwater to irrigate their own land using small, inexpensive water pumps, depleting groundwater stores.
Water is also used to produce hydroelectricity in the Hindu Kush Himalayan region, with most dams located along the Ganges and Indus rivers. Changes in the hydrologic cycle in the Himalayas will have implications for power production, and rising temperatures will increase the loss of water stored in dams to evaporation.
Water resource management and the provision of clean water and sanitation is already a challenge in the region. The adequacy and effectiveness of existing water management institutions, which focus on natural hazards and disaster reduction, could provide an indicator of how the region will likely cope with changes in water supply. Here, a woman in a village in rural India pumps water for her family on Independence day (hence the worn flags). Image Source: mckaysavage/Flikr, http://www.flickr.com/photos/mckaysavage/2832930606/
To effectively respond to the effects of climate change, water management systems will need to take account of the social, economic, and ecological complexities of the region. This means it will be important to expand research and monitoring programs to gather more detailed, consistent, and accurate data on demographics, water supply, demand, and scarcity. Here, researchers stand on the Chhota Shigri Glacier in the Indian Himalaya. Image source: Mark W. Williams, University of Colorado, Boulder.