A Preliminary Assessment of the Snow Cover of the Upper Indus Basin and Contribution to Water Resources Richard Armstrong, CIRES/NSIDC, University of Colorado Adina Racoviteanu, INSTAAR, University of Colorado Donald Alford, Consulting Hydrologist, Billings Montana Mark Williams, INSTAAR, University of Colorado Siri Jodha Singh Khalsa, CIRES/NSIDC, University of Colorado Al Rasmussen, University of Washington, Seattle Project Funding from World Bank, NASA, USAID

Eastern Himalayan Range - Nepal

- Digital elevation model (DEM) from the NASA Shuttle Radar Topography Mission (SRTM v.4) (90m spatial resolution). - Glacier outlines for Nepal from topographic maps and satellite data (GLIMS/ICIMOD) - Catchment basins from ICIMOD (basic topographic unit in water budget analysis) -Runoff data from Department of Hydrology and Meteorology (DHM) Nepal Data Sources 3 Estimating runoff from glacier ice melt in Nepal using area-altitude distributed models

Compute melt below 5400 m using a regional vertical mass balance gradient. (from Alford et al. 2010, Glacier retreat in the Nepal Himalaya: An assessment of the role of glaciers in the hydrologic regime of the Nepal Himalaya. Report to SASDN, The World Bank.) Estimated 0 o C isotherm altitude Area-elevation hypsometry and location of 0 o isotherm for the glacier covered area of Dudh Kosi Basin, Nepal = Approximately 5400 m

Compute runoff from melting glacier ice – Accumulation area Ablation area 1.4m2.8m4.2m5.6m Runoff Volume = sum of the products of the specific net budget within the (100 m) elevation bands within the ablation zone and surface area of those elevation bands. In this study:VBG db/dz = 1.4 m/ 100m for probable maximum runoff volume from ice melt for the region.

Results of Nepal Study  The contribution of glacier ice melt to annual streamflow volume varies among the 9 sub-basins from approximately 2-30%.  This glacier ice melt contribution is estimated to be about 4% of the total mean annual streamflow volume of the rivers flowing out of Nepal.  Mass balance gradient and degree day melt models produce comparable results.  Similar results were reported by Thayyen and Gergan in The Cryosphere 4, 2010 for the Dokriani glacier, Nepal. 6

Western Himalaya, Upper Indus Basin

Upper Indus Basin = catchment above Besham/Tarbela

Armstrong, NSIDC/U. of Colorado Estimate Water Sources for the flow of the Upper Indus Involve the relative percentages of rainfall, seasonal snow cover melt, and glacier ice melt. (infiltration, ground water, evaporation) Although numerous publications address this pattern, there is limited agreement on the contribution from these individual sources: primary source is glacier ice and “semi-permanent snow cover”, with rainfall and seasonal snow being insignificant, runoff is equally divided between snow and glacier melt, two thirds from snow/ice but without a clear distinction between snow melt and glacier melt,

Armstrong, NSIDC/U. of Colorado in other examples, melt specifically from glaciers is noted to be of lesser importance simply because glaciers only occupy a limited amount of area in the UIB. One source of these differences is often the lack of consistent definitions for semi-permanent snow cover and seasonal snow cover. The assessment presented here focuses on seasonal snow cover, defined as that snow cover that has accumulated during the previous winter, or snowfall season, prior to the current melt season.

Besham- Tarbela Dam 340m AMSL Besham- Tarbela Dam 340m AMSL

Besham Approximately 107,000 sq. km are situated above Pangong Lake and its associated internal drainage. Formerly, Pangong Lake had an outlet to Shyok River, a tributary of Indus River, but it was closed off due to natural damming. Defining the Upper Indus Basin Some examples with a greater total area of approximately 200,000 to 273,000 sq. km include the region situated above Pangong Lake which we have considered to be internal drainage and therefore was not included in the map shown below which has an area of 166,101 sq. km above Besham. This is the basin polygon we have been working with for our snowcover and glacier mapping.

MODIS Mean Monthly Snow Covered Area (SCA) km 2

Departures from MODIS mean monthly snow covered area for Astore, Gilgit, Hunza, Shigar, and Shyok sub-basins,

Departures from the MODIS mean snow covered area for the full UIB.

August – annual minimum, semi-permanent snow and glaciers Upper Indus Basin Seasonal Snow Area February – annual maximum seasonal snow cover

Armstrong, NSIDC/U. of Colorado If snow present, and melt possible, (NCAR/NCEP upper air temperatures) apply PDD model to area-elevation data to generate local melt volumes (potential runoff). Mean monthly area-elevations for seasonal snow cover in the UIB.

Armstrong, NSIDC/U. of Colorado Average monthly values for snow melt and stream flow

Armstrong, NSIDC/U. of Colorado

Besham/ Tarbela Resevoir Preliminary estimates of average contribution to annual flow at Besham: Snow Melt 75% Glacier Ice Melt 15% Rainfall 10% 20

Conclusions Eastern Himalaya: river runoff dominated by summer monsoon – snow/ice play minor role. Western Himalaya, Karakoram, Hindu-Kush: seasonal snow and glacier ice melt are major contributors to water resources. Snow and glacier cover in the west appears to be reasonable stable over the past decade. Well-planned management, conservation, and efficient use of water currently available – as important as any changes that may take place in the regional climate in the near future. Need remains for accurate estimates of potential impact of reduced seasonal snow or glacier melt contribution to downstream water resources in a warming climate.

GLIMS Database at NSIDC High resolution glacier outlines (shape files) derived primarily from Landsat, ASTER and SPOT Current content: 95,000 glaciers, 290,000 km 2 Coming soon: ESA GlobGlacier Project (European Alps, West Greenland, Sweden, Baffin Island) Svalbard, Argentina, Nepal, and China. GLIMS database contains approximately 250,000 ASTER browse images.

Richard L. Armstrong CIRES/NSIDC, Univ of Colorado Boulder, USA The Glaciers of the Hindu Kush-Himalayan Region A summary of the science regarding glacier melt/retreat in the Himalayan, Hindu Kush, Karakoram, Pamir, and Tien Shan mountain ranges All ICIMOD Publications: