The behaviour of glaciers in the Karakorum and western Himalayas is not quite clear; there is evidence suggesting that while some of these glaciers are retreating, others are advancing. This behaviour has been termed the ‘Karakorum anomaly’. The contrasting behaviour of glaciers across the HKH region is a challenge for scientists in terms of understanding the climatic factors that determine glacier advance and retreat. However, it is clear that one single force does not govern the whole region.
One of the reasons why scientists continually attempt to unfold the climate-glacier relationship is the perceived importance of glaciers to regional water resources. The glaciers of the Himalayan region are estimated to hold 3,700 cubic kilometres of ice—a significant quantity of stored water—and are delivering freshwater at a gradual pace. Water generated by the melting of glaciers is generally considered to be crucial to sustaining the river systems originating in the HKH, particularly when there is no rainfall contributing to runoff. The shrinkage of glaciers could have a marked negative impact on the water resources of the Himalayan basins. Serious attempts have been made in recent years to quantify the possible impact of climate change and fluctuations in glaciers on the water resources of the region. These studies have provided important insights into this topic and interestingly, have revealed great regional differences in the role of glaciers in maintaining water resources.
A study by Armstrong and others published in 2009 suggests that glacier melt contributes only 4 percent of the estimated 200,000 million cubic metres of water flowing annually from the rivers of Nepal. This result is confirmed by a more recent study by Andermann and others indicating that groundwater has a more important role than glacier melt in the hydrology of Nepal. Immerzeel and others published a study earlier this year based on the Langtang Khola catchment in Nepal; even at this scale (about 350 square kilometres), it was found that changes in climate change and glacier melt are not likely to lead to a drastic reduction in water resources.
In contrast, the river basins in the western part of the HKH region, which are less dominated by the summer monsoon, seem to be more sensitive to climate change and glacier shrinkage. A comprehensive comparison among several basins in the HKH conducted by Immerzeel and others in 2010 found that the Indus basin is far more sensitive to climate change, as discharge generated by snow and glacial melt is 151 percent of the total discharge naturally generated in the downstream part of the basin, which is snow and glacier free.
One of the reasons scientists study climate-glacier relation is the perceived importance of glaciers to regional water resources.
It should be noted that that the studies mentioned above have many limitations and uncertainties. The first level of uncertainty is in the climate projections—because of the inability of existing climate models to adequately represent the climate of the rather complex HKH region. The second level of uncertainly comes from our limited understanding of the climate-glacier relationship and the inability to quantify this relationship. The third level of uncertainty derives from an inability to translate glacier fluctuations under the changed climatic conditions into melt water generation across the complex ecological and geophysical systems of the large basins of the region. To have more confidence in the estimates, it is essential to strengthen our research efforts on climate, glaciers, and their connection with water resources by using enhanced observation systems, monitoring, and modelling across the HKH region. Despite the uncertainties, recent studies do provide an indication of the ‘hot spots’ for water resources in the HKH region, which can be used to prioritize research endeavours.
The author is a Climate Change Specialist with ICIMOD
abshrestha@icimod.org
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