Summary
Climate change is causing significant mass loss of glaciers in high mountains worldwide. Although glacier systems show a great amount of inherent complexity and variation, there are clear overall trends indicating global glacier recession, which is likely to accelerate in coming decades. Large gaps remain in our understanding and ability to model accurately the key processes and cause-effect relationships driving glacier re- sponse to climate change. In addition, a lot of data on glacier mass changes are not available to the public due to national interests concerning water supply.
Impacts of the shrinkage and disappearance of mountain glaciers include changes in the flow characteristics of glacier- fed rivers, glacier lake outburst floods (GLOFs) in the Andes and Asia, and changing flood severity and frequency. GLOFs were observed in Patagonia in 2008 and 2009, in addition to GLOFs in the Himalayas and Andes in the past decades in areas where glaciers are receding. While such GLOFs may immediately endanger lives, infrastructure and power sup- ply, flash floods and particularly large-scale down-river floods pose an ever greater challenge and risk. These floods are caused by extreme events of intense and high-volume mon- soons or other types of rains that are often exacerbated by un- sustainable land use practices killing several thousand people every year directly, and impacting over 100 million people annually, including through loss of crops and eruption of dis- eases associated with flooding of sewage or contamination of drinking water supplies.
The glacial contribution to river flow varies greatly, both annually and within and between catchments. The hydro- logical significance of glacier runoff also depends on other components of the hydrological cycle, such as precipitation, evapo-transpiration, and groundwater flow. In consequence, the impacts of glacier mass loss will be highly variable both locally and worldwide. Some regions will undoubtedly be af- fected by water shortage, whereas others are unlikely to be
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significantly affected by glacial melt. Much detailed work remains to be done to adequately predict regional and local hydrological responses to climate change. Flood risks are expected to increase in some regions, including increased frequencies of GLOFs and weather-related flash floods in both the Hindu Kush Himalayas and in the Andes. Melting of glaciers and ice caps will also have global effects on sea level rise. It is currently estimated that they will contribute approximately 40 to 150 mm (depending upon the green- house gas scenario and climate model used) to sea level rise by 2100.
Changes in glacier regimes and runoff from snow and ice, combined with changes in precipitation timing and intensity will most likely increase human vulnerability in many areas. Livelihoods are affected as climate variability and water stress affect agriculture, forestry, health conditions and tourism. Future challenges for the management of impacts of climate change include filling data gaps, improving regional coopera- tion in observation networks and developing comprehensive databases, improving modeling of glacier mass balance and runoff, strengthening regional cooperation and developing adaptive strategies that are cultural and context specific, and ensuring sufficient irrigation capacity to uphold higher levels of food production.
One of the chief challenges in the coming decades will be to capture and store excess water during periods of high water availability. We are likely to experience more extreme melt- ing, as well as extreme events of rainfall. With great land-use pressures in many mountain regions, including deforesta- tion and heavy grazing combined with extreme rainfall, flash- floods and flooding will likely increase. New and more effec- tive systems in both capturing and storing water will become essential in the future. This includes both installation of new water capture and storage methods, as well as re-introduction of some of the ancient traditional irrigation systems, such as