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Summary The hydrograph separation method, previously proposed to quantify base flow, seasonal snowmelt, and glacial melt components in river flows within Upper Indus basin underestimates glacial melt component. This is particularly limiting for highly glacierized watersheds. The limitation has been corrected by a further refinement of the method. The results with the refined procedure are highly consistent with the physical characteristics such as hypsometry and glacier extents of the watershed even though the method itself is completely independent of the physical characteristics of the watershed where it is applied. Glacial melt far outweigh snowmelt in the rivers draining the Karakoram and Zanskar ranges. In the Karakoram, on an annualized basis, glacial melt proportion varies from 43% to 50% whereas snowmelt varies from 27% to 31%. On the other hand, snowmelt dominates over glacial melt in the rivers draining the western Greater Himalayas and the Hindu Kush. Here snowmelt percentage in river discharge varies from 31% to 53% whereas that of glacial melt ranges from 16% to 30%. In the main stem of Upper Indus River, snowmelt fraction in most cases is slightly greater than the glacial melt fraction. In the main stem, snowmelt percentage ranges from 35% to 44% whereas glacial melt percentage ranges from 25% to 36%. Upper Indus River just upstream of Tarbela Reservoir carries annual flows constituted of 70% melt water of which 26% is contributed by glacial melts and 44% by snowmelts. We also show that during the later part of twentieth century and continuing into the early part of twenty first century glacial melt contributions to river discharge has decreased compared to the previous decades. This phenomenon can be ascribed to either basin wide loss of glacial mass in the recent decades in the elevation range from where most of the glacial melt originates or glacier growth and stability due to either reduction in energy inputs or increase in precipitation or both at the high altitude bands wherefrom glacial melt water originates. [ABSTRACT FROM AUTHOR]

Summary The Hindukush Karakoram Himalayan mountains contain some of the largest glaciers of the world, and supply melt water from perennial snow and glaciers to the Upper Indus Basin (UIB) upstream of Tarbela dam, which constitutes greater than 80% of the annual flows, and caters to the needs of millions of people in the Indus Basin. It is therefore important to study the response of perennial snow and glaciers in the UIB under changing climatic conditions, using improved hydrological modeling, glacier mass balance, and observations of glacier responses. However, the available glacier inventories and datasets only provide total perennial-snow and glacier cover areas, despite the fact that snow, clean ice and debris covered ice have different melt rates and densities. This distinction is vital for improved hydrological modeling and mass balance studies. This study, therefore, presents a separated perennial snow and glacier inventory (perennial snow-cover on steep slopes, perennial snow-covered ice, clean and debris covered ice) based on a semi-automated method that combines Landsat images and surface slope information in a supervised maximum likelihood classification to map distinct glacier zones, followed by manual post processing. The accuracy of the presented inventory falls well within the accuracy limits of available snow and glacier inventory products. For the entire UIB, estimates of perennial and/or seasonal snow on steep slopes, snow-covered ice, clean and debris covered ice zones are 7238 ± 724, 5226 ± 522, 4695 ± 469 and 2126 ± 212 km 2 respectively. Thus total snow and glacier cover is 19,285 ± 1928 km 2 , out of which 12,075 ± 1207 km 2 is glacier cover (excluding steep slope snow-cover). Equilibrium Line Altitude (ELA) estimates based on the Snow Line Elevation (SLE) in various watersheds range between 4800 and 5500 m, while the Accumulation Area Ratio (AAR) ranges between 7% and 80%. 0 °C isotherms during peak ablation months (July and August) range between ∼ 5500 and 6200 m in various watersheds. These outputs can be used as input to hydrological models, to estimate spatially-variable degree day factors for hydrological modeling, to separate glacier and snow-melt contributions in river flows, and to study glacier mass balance, and glacier responses to changing climate. [ABSTRACT FROM AUTHOR]

Highlights: [•] Summer river flows in central Karakoram conspicuously exhibit rising trends. [•] Rate of loss of glacial storage is approximately 0.04–0.05mm/day/year. [•] Increasing summer precipitation is responsible for nonnegative glacial mass balance. [•] Rising river flows accompany nonnegative glacial mass balance in central Karakoram. [ABSTRACT FROM AUTHOR]

Highlights: [•] Auto pit-filling applied to DEMs can result in significant errors in catchment areas. [•] Past estimates of the Upper Indus Basin area are ranging between 160,000 and 266,000km2. [•] The best estimate of the Upper Indus Basin (UIB) area is 164,867km2, using SRTM DEM. [•] The Pangong Tso catchment is not part of the UIB, for at least past thousand years. [•] Past studies based on the over-estimated watershed areas of the UIB need revision. [Copyright &y& Elsevier]

Highlights: [•] Glacio-hydrometeorological conditions with four flow regimes in Upper Indus Basin. [•] Highest flow regime from July to September carry 53–62% annual flow volumes (m3). [•] Three most glaciated watersheds contribute 48–54% flow to the highest flow regime. [•] Melt water from altitude >3500m constitutes 41–54% of annual flow volumes. [•] Near the outlet, glacial and snow melt components respectively constitute 21% and 49% of annual flows. [Copyright &y& Elsevier]

• Constant ice density assumption produces significant bias. • Glaciers in the Indus are losing mass similar to the rest of Asia. • The western and central Karakoram glaciers are losing negligible mass. • Indus Basin contributes about 0.014 mm a−1 to global sea-level rise. Glaciers in the upper Indus supply more than half of the river water, are experiencing significant melting with a debated fate. The recent melting rate is still contained by considerable uncertainties, hindering to estimate precise glacier mass change. Here we present geodetic mass balance results for the whole Indus Basin using SRTM and ALOS 30 m elevation data, improved glacier inventory, optimized glacier surface density, and validation through in-situ differential GPS and ICESat data. Our glacier inventory and derived by improving RGI6.0 boundaries and separated into debris cover and debris free parts. The derived surface elevation changes were converted into annual mass balances using separated density assumptions (four criteria) for debris-covered ice (900 ± 60 kg m−3), debris-free ice (below 20° and 25° slopes (850 ± 60 kg m−3) and above 20° and 25° slopes (600 ± 60 kg m−3)), respectively. The resulting mass balance biased between −0.20 and 0.09 m water equivalent (w.e.) a-1 using an average (850 ± 60 kg m−3) density assumption throughout the Indus Basin. In the western Himalaya and Hindu Kush, the glacier mass losses are less affected by the average density assumption compared to the Karakoram. The western (Hunza) and central (Shigar) Karakoram glaciers show negligible mass losses of −0.02 ± 0.12 and −0.01 ± 0.13 m w.e. a−1 in contrast to the relatively more negative mass balance (−0.26 ± 0.21 m w.e. a−1) in the eastern (Shyok) Karakoram. All the sub-basins exhibit negative mass balances, with the most negative values ranging from −0.34 ± 0.31 to 0.44 ± 0.27 m w.e. a−1 in the Ravi, Chenab and Jhelum sub-basins of the Himalaya. The whole Indus Basin contributes approximately +0.014 ± 0.016 mm a−1 to the global mean sea-level equivalent. [ABSTRACT FROM AUTHOR]