Variability of snow cover extent and snow melt runoff in the Himalaya-Karakoram
Abstract
Melt water from seasonal snow cover and glacier ice is a significant component of runoff in drainage basins in High Asia. In previous studies, model-based estimates for the Ganges River basin above Farraka, India, the lowest gauge in the basin, indicate snow melt runoff contributes about 10% of the total runoff. The contribution from melting glacier ice is smaller; studies report less than about 4%. Snow melt contributions for head water sub-catchments where rainfall inputs are smaller are about 20%. The snow melt contribution in the Indus basin is larger because summer monsoon rains do not influence this basin. However, these model-based estimates are influenced strongly by biases in forcing data and uncertainties in the models themselves. Here we present estimates of snow and ice melt runoff based on a temporally and spatially continuous time series of snow extent derived from the gridded MOD10A1 daily snow cover product and melt depth calculated using a simple temperature index model. Snow melt runoff for a given grid cell is the daily melt depths summed for the period a grid cell is snow covered. These runoff estimates implicitly include glacier melting because snow maps do not distinguish between snow and ice surfaces. Using satellite-derived measurements of snow on the ground avoids having to use gridded precipitation, which can be biased, especially in mountain regions. Time series of snow extent and snow melt runoff are presented for 2000 to 2011 for five head water basins of the Indus and Ganges rivers that form a transect along the Himalaya-Karakoram chain, spanning the monsoon influenced eastern Himalaya and the arid Karakoram. The temperature index melt model is forced with air temperatures from the NASA MERRA, ERA-Interim and NOAA-CFSR reanalyses, providing a range of estimates of melt depth. This range provides a measure of uncertainty for estimates of snow melt runoff. Air temperatures from the three reanalyses show significant differences with strong spatial structure. These differences translate into differences in melt depth. Biases need to be addressed in forcing fields in order to obtain robust estimates of snow melt runoff for this region.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2012
- Bibcode:
- 2012AGUFMGC52B..04B
- Keywords:
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- 0740 CRYOSPHERE / Snowmelt;
- 1884 HYDROLOGY / Water supply