Potential Impacts of Snow and Ice Changes on Water Availability for People in High Mountain Asia
Abstract
Rivers are central to life in central and southern Asia, where water diversions support agriculture and runoff is used to generate hydroelectric power. Runoff is composed of rainfall, snowmelt, and glacial ice melt. Changes in snow and ice resources raise questions about possible impacts on people. How much runoff comes from snow, glaciers, and rain at different points along a stream network? Understanding variability in timing, amount, and spatial coverage of snowfall and glacier ice volume is relevant to assessing vulnerability.
USAID has supported the Contribution to High Asia Runoff from Ice and Snow (CHARIS) project to investigate how much rain, snow, and glacier melt contribute to river runoff, in partnership with 11 Asian institutions. Our results show that in the summer, melting glacier ice contributes significantly to river flow in the western basins (Syr Darya, Amu Darya, and Indus) but less so in the east (Ganges and Brahmaputra basins) where monsoonal rains occur. Melting snow contributes much more, proportionally, than water from all other sources for all basins except for the Ganges, where rainfall predominates. This study examines the potential impacts of cryospheric changes on water availability for human consumption. We calculate the contributions to streamflow from these three sources at 500 m elevation intervals in each of five major basins, normalized by the estimated human population above that point. This gives the total annual volume of water available per person from the sources. For the Amu Darya and Syr Darya river basins, meltwater from exposed glacier ice makes up more than 10% of the water theoretically available to each person only for elevations above 4000 m. The per-person annual contribution to streamflow from glacier melt is small for the Indus (< 5%) and negligible for the Ganges and Brahmaputra at all elevations. Even where the fraction of runoff coming from glaciers is small, glaciers still modify the seasonal and inter-annual variability of runoff, both by releasing runoff later in the melt season and effectively smoothing year-to-year variations in streamflow. Water diversions, major reservoirs, the use of groundwater, and timing of precipitation and melt impact the per-person partitioning differently in different locations and would likely alter our conclusions in such locations.- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFMPA11A..09R
- Keywords:
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- 1630 Impacts of global change;
- GLOBAL CHANGEDE: 1637 Regional climate change;
- GLOBAL CHANGEDE: 6304 Benefit-cost analysis;
- POLICY SCIENCESDE: 6309 Decision making under uncertainty;
- POLICY SCIENCES