Combining Remote Sensing And Isotopic Analysis To Determine The Contribution Of Snow- And Ice-Melt To Streamflow In The Nepal Himalaya: A Multi-Scale Approach
Racoviteanu, Adina E 1 ; Armstrong , Richard 2 ; Williams, Mark W. 3 ; Alford , Don 4 ; Cowie, Rory 5
1 Dept of Geography and Institute of Arctic and Alpine Research, University of Colorado
2 National Snow and Ice Data Center, University of Colorado
3 Dept of Geography and Institute of Arctic and Alpine Research, University of Colorado
4 4 1831 Poly Drive, Billings, MT
5 Dept of Geography and Institute of Arctic and Alpine Research, University of Colorado
Recent controversies about the retreat of Himalayan glaciers pose concerns about the future of water supplies in this region. While snow and ice are an important component of the hydrologic regime of many large mountain ranges including the Himalaya, the role of glaciers in the hydrologic regime of this mountain range, in particular their contribution to base flow, is not well understood. Here we focus on assessing the relative contributions of snow- and ice-melt to base flow in selected basins of the Eastern Himalaya (Nepal). This research combines remote sensing-derived glacier data from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and the Shuttle Radar Topography Mission (SRTM) with field-based measurements of streamflow and water chemistry. Our approach relies on ablation gradients, the area-altitude distributions of glaciers, degree-day approaches and mixing models. Based on the ablation gradient method, we estimate that the contribution of glacier annual melt water to annual streamflow into the Ganges basin from the glacierized catchments of the Nepal Himalaya represents 2-3% of the total annual streamflow volume of the rivers of Nepal.
Preliminary results from the Langtang and Dudh Kosi basins using stable water isotopes collected during baseflow conditions in November 2008 and December 2009 show that glacial outflows at about 4600m have delta18O values of about -16 parts per mil. The delta18O values increase by about 1 part per mil at an elevation of 3300 m in river flow, and by 3 parts per mil at an elevation of 1400 m. These results suggest that glacial contributions to discharge decrease rapidly with decreasing elevation and increasing basin area, consistent with the results from the ablation modeling above.
Alford, D., Armstrong, R. and Racoviteanu, A. 2009. Glacier retreat in the Nepal Himalaya: An assessment of the role of glaciers in the hydrologic regime of the Nepal Himalaya. (in press), South Asia Sustainable Development Office, Environment and Water Resources Unit, The World Bank, Washington, DC.