Himalayan Glaciers: Climate Change, Water Resources, and Water Security (2012)Board on Atmospheric Sciences and Climate
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Scientific evidence shows that most glaciers in South Asia's Hindu Kush Himalayan region are retreating, but the consequences for the region's water supply are unclear, this report finds. The Hindu Kush Himalayan region is the location of several of Asia’s great river systems, which provide water for drinking, irrigation, and other uses for about 1.5 billion people. Recent studies show that at lower elevations, glacial retreat is unlikely to cause significant changes in water availability over the next several decades, but other factors, including groundwater depletion and increasing human water use, could have a greater impact. 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.
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- The meltwater from glaciers in the Hindu Kush Himalayan region, which covers eight countries across Asia, supplements several great river systems such as the Indus, Ganges, and Brahmaputra. Scientific evidence shows that most glaciers in the Himalayan region are retreating, leading to concerns that, over time, normal glacier melt will not be able to contribute to the region's water supply each year.
- Glaciers in the eastern and central regions of the Himalayas appear to be retreating at rates comparable to glaciers in other parts of the world. In the western Himalayas, glaciers are more stable and may even be increasing in size. There is uncertainty in projections of future changes in precipitation, but shifts in the location and intensity of snow and rain could also impact the rate of glacial retreat.
- Variations in climate; in the timing, amount, and type of precipitation; and in glacial behavior and dynamics across the vast Hindu Kush Himalayan region mean that it is challenging to determine exactly how retreating glaciers will affect water supply in each location. It is likely that the contribution of glacier meltwater to water supply in the Hindu Kush Himalayan region may have been overestimated in the past, for example by not differentiating between the contributions to water supply of meltwater from glaciers and meltwater from snow.
- Overall, retreating glaciers over the next several decades are unlikely to cause significant changes in water availability at lower elevations, which depend primarily on monsoon rains. However, for high elevation areas, current glacier retreat rates, if they continue, could alter streamflow in some basins. Assuming annual precipitation in the form of snow and freezing rain remains the same, the loss of water stored as glacial ice will likely not change the amount of meltwater that supplements rivers and streams each summer.
- Glacial meltwater can act as a buffer against the hydrologic impacts of a changing climate, such as drought. Thus, water stored as glacial ice could serve as the Himalayan region's hydrologic insurance. Although retreating glaciers would provide more meltwater in the shorter term as the glacier shrinks, the loss of glacier "insurance" could become problematic over the longer term.
- Groundwater is an integral part of the Hindu Kush Himalayan region's hydrology, although uncertainties about its contributions to water supply are great. It is clear that groundwater is already being depleted in many areas, with evidence that in the central Ganges Basin, overdraft of groundwater is likely to have an earlier and larger impact on water supplies than foreseeable changes in the supply of glacial meltwater.
- Social changes such as changing patterns of water use and water management decisions, are likely to have at least as much of an impact on water demand as environmental factors do on water supply. Many of the region's river basins are already water stressed, and this water stress could intensify as populations grow. Water scarcity will likely affect the rural and urban poor most severely, as these groups have the least capacity to move to new locations as needed.
- It is predicted that the region will become increasingly urbanized as cities expand to absorb migrants in search of economic opportunities. As living standards and populations rise, water use will likely increase—for example, as more people eat diets rich in meat, more water will be needed for agricultural use. The effects of future climate change could further exacerbate water stress.
- Water resources management and the provision of clean water and sanitation is already a challenge in the Hindu Kush Himalayan region. The adequacy and effectiveness of existing water management institutions, which focus on natural hazards and disaster reduction, provides an indicator of how the region will likely cope with changes in water supply.
- Although the history of international river disputes suggests that cooperation is more likely than violent conflict, current political disputes in the region could complicate the process of reaching agreements on resource disputes. Changes in the availability of water resources could play an increasing role in political tensions, especially if existing water management institutions do not better account for the social, economic, and ecological complexities of the region.
- 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.