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Satellite-geodetic altimetry investigations in the Karakoram have indicated slight mass gain or loss of the glaciers during the early part of 21st century. Equivalent discharge in the upper Indus Basin due to these mass changes has been estimated at 5 to 10% of mean annual flow. However, satellite altimetry and geodetic glacier mass estimates in the extreme topography of the Karakoram have not yet been counter-validated by hydrological analysis. Therefore, we present a first cross validation of three to five decades of river flow data from the three major watersheds in the Karakoram, with matching series of monthly precipitation, temperature, and evaporation provided by six atmospheric reanalysis products for 1979-2014. The analyses suggest that in most cases river flows have been increasing steadily from the end of the 1960s and 1970s to the middle of the 1990s and have stabilized or are in decline since then. Hunza watershed in Karakoram West shows consistently declining flows over the first half of the analysis period and stable flows during the second half for most of the summer melting season, suggesting mass accumulation. Rising river flows in the Shyok and Shigar watersheds, followed by stabilizing or slightly declining flows from 1995 onward, can be explained by consistently increasing precipitation during the first half of the analysis period, and successive stabilization or minor decline thereof. Flow data do not necessarily suggest considerable loss or gain of glacial mass in the Karakoram during the late 90s and early 2000s as suggested by satellite-based altimetry studies. [ABSTRACT FROM AUTHOR]

Field observations and geodetic measurements suggest that in the Karakoram Mountains, glaciers are either stable or have expanded since 1990, in sharp contrast to glacier retreats that are prevalently observed in the Himalayas and adjoining high-altitude terrains of central Asia. Decreased discharge in the rivers originating from this region is cited as a supporting evidence for this somewhat anomalous phenomenon. Here, we show that river discharge during the melting season of the glaciers in the eastern and western Karakoram, respectively, exhibits rising and falling trends. We have implemented a statistical procedure involving non-parametric tests combined with a benchmark smoothing technique that has proven to be a powerful method for separating the stochastic component from the trend component in a time series. Precipitation patterns determined from ERA-40 and GPCP data indicate that summer-monsoonal precipitation has increased over the Karakoram Mountains in recent decades. Increasing flows in June and July in the eastern Karakoram are due to an increase in summer-monsoonal precipitation. The rising trend of August discharge is due to an increase in the loss of glacier storage at an approximate average rate of 0.186–0.217 mm d-1year-1during the period 1973–2010. Moreover, this rate is higher than the rate of increase in monsoonal snowfall during the months of August and September. Therefore, most plausibly, glacier mass balance in the eastern Karakoram is negative. In the western Karakoram, river flows show declining trends for all summer months for the period 1966–2010, corresponding to a rate of increase of glacier storage by approximately 0.552–0.644 mm d-1year-1, which is also higher than the rate of increase in summer-monsoonal precipitation. The gain of the cryospheric mass in the western Karakoram is in the form of increased thickness of the glaciers and perennial snowpacks instead of areal expansion. This investigation shows two contrasting patterns of trends of river flows that signify both negative and positive mass balance of the Karakoram glaciers. Trends of river flows are spatially and temporally integrated responses of a watershed to changing climate and thereby are important signals of the conditions of the cryospheric component of a watershed where it is highly significant. However, they cannot unequivocally provide indications of the state and fate of the glaciers in the complex hydrometeorological setting of the Karakoram. Extreme caution and care must be exercised in interpreting trends of river discharge in conjunction with climatic data. [ABSTRACT FROM AUTHOR]

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]

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: [•] 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]

A prevailing perception is that the glaciers and perennial snow and ice covered areas (SCAP) or in the Himalayan region are fast contracting. However, systematic studies providing the quantitative estimates of SCAP as a function of time within individual river basins are lacking. The importance of meltwater in river flows varies greatly from one river basin to another, yet the actual estimates of those contributions are largely unknown. This study bridges such knowledge gaps for the upper-middle Brahmaputra Basin by using best available digital cartographic and remotely sensed snow cover data. We find that when the entire basin is considered, SCAP decreased from 7637 ± 764 in 1980 to 4298 ± 1422 km2 in 1992. However, it has increased to 7160 ± 2248 km2 in 2000. From 2000 to 2010, the SCAP has remained nearly constant around a mean of 10 052 ± 1468 km2. The same trend is observed within individual physiographic zones of the basin. Such increase in SCAP is due to the increase in the precipitation over the middle Brahmaputra Basin and the Nyainquentanglha Mountains, as observed in station records. The incursion of moist air through the Brahmaputra valley to the higher elevations within the Nyainquentanglha Mountains causes snowfall during pre-monsoonal and post-monsoonal seasons and an expansion of the SCAP. Glacial expansions in the Nyainquentanglha Mountains have also been observed in other recent studies. In addition to the increase in precipitation and SCAP, another manifestation of climate change observed in this basin is the increasing temperature with a mean annual trend of +0.28 °C/decade. The hydrologic consequences of the observed effects of climate change are expected to be an insignificant change in streamflows in the watersheds drained by the upper Brahmaputra River but a perceptible increase in river discharges in the watersheds drained by the middle Brahmaputra River and its tributaries, particularly within the upper and lower catchments of the middle Brahmaputra Basin. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Integrated water resources management at river basin scales and evaluation of effects of climate change on regional water resources require quantitative estimates of space-time variability of monthly discharges within a river network. This study demonstrates that such estimates, which can be called stream water availability, for regional river basins with meager or nonexistent gauge data, can be obtained by combining continuity models of hydrological processes, flow routing, and topology of the river basin. The hydrologic processes can be adequately modeled using high quality databases of hydrologic significance. A stream water availability model is presented for Upper Indus Basin (UIB) utilizing the most up-to-date datasets for topography, temperature, precipitation, net radiation, land cover, soil type, and digital atlas. Multiple datasets have been evaluated and the ones with best accuracy and temporal coverage have been selected for the final model. Upper Indus River and its major tributaries are highly significant in regional water resources management and geopolitics. However, UIB is a poorly studied and largely ungauged river basin with an area of 265,598 km and extremely rugged topography. Several factors, the chief ones being the challenging terrain and the trans-boundary nature of the basin, have contributed to this knowledge gap. Hydro-climatologically it is a complex basin with a significant cryospheric component. The spatial and temporal variation of the principal climatic variables, namely precipitation, net radiation, and temperature has been thoroughly accounted for in the development of a stream water availability model based on a process model coupled with a topologic model and a linear reservoir model of river flow routing. Model calculations indicate that there are essentially two hydrologic regimes in UIB. The regime that is truly significant in contributing stream flows, originates from the UIB cryosphere containing outstanding glaciers and snowfields. The other regime, generated from wet precipitation and melt water from seasonal snow covers is insignificant due to high rates of infiltration and evaporation in the semi-desert environment prevailing at elevations below perennial snow and ice covers. In general, the modeled stream flow characteristics match with the sparse discharge measurements that are available. Flow in the Indus considerably increases at its confluence with Shyok River and further downstream where other tributaries form the north join the main stem. At or near the outlet of the basin stream flow can vary from less than 800 m s in the winter and spring to nearly 8,000 m s in the peak summer and can persist to over 1,500 m s in the autumn. The importance of snow and glacial melt in Indus River discharge is apparent and any global or regional climate change affecting the equilibrium line elevation of the snow fields in the Karakoram will have a profound influence on the water availability in the Indus. Estimates are made for per capita water availability in Ladakh and Gilgit-Baltistan territories, controlled by India and Pakistan respectively. Geopolitical significance and climate change effects are discussed briefly. [ABSTRACT FROM AUTHOR]