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Upper Indus Basin (UIB), being climatologically sensitive and socio-economically important, has emerged as a hotspot for eco-hydrological studies. Permafrost, one of the essential components of the regional hydrological cycle with a critical role in microclimate, is also an important water resource in the UIB. Despite being an important component of the cryospheric system, permafrost is least studied in the UIB. In present study, we used stable oxygen and hydrogen isotopic composition in supra-permafrost water (SPFW) and aufeis along with precipitation, snowpack, glacier and other groundwaters to assess their variability and estimate their contribution to regional hydrology. The sources are evolving isotopically, depending on physiographic and hydrometeorological factors, with each source attaining different (if not distinct) isotopic signatures. The isotopic signatures (with different ranges) of sources help in estimating the contribution from these sources. A significant altitude gradient of δ18O is observed in stream water, SPFW and other groundwaters. Isotopic composition in SPFW is differentially modulated by fractionation, resulting in isotopic variability from the source waters. The results suggest snowmelt and/or glacier melt as the source of SPFW. To stream flow, SPFW is the dominant contributor (43 ± 18 %) at higher elevations (> 4300 m a.m.s.l.) in July, followed by snowmelt (26 ± 10 %). In September, SPFW contribution decreases (14 ± 8 %), but the contribution from other groundwaters becomes dominant (39 ± 11 %) to stream flow. The results indicate the significant role of seasonal thawing and freezing of active layer on the contribution from SPFW. This study highlights the significant role of permafrost in the hydrological system of the basin. The study also emphasizes the need to understand the dynamics of permafrost, taliks of various types (e.g., supra-permafrost subaerial talik) and active layer under changing climate to define the subsequent implications to regional hydrology, eco-hydrological systems and micro-climate of permafrost regions.

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Recent studies have endorsed that surface water chemical composition in the Himalayas is impacted by climate change-induced accelerated melting of glaciers. Chemical weathering dynamics in the Ladakh region is poorly understood, due to unavailability of in situ dataset. The aim of the present study is to investigate how the two distinct catchments (Lato and Stok) drive the meltwater chemistry of the Indus River and its tributary, in the Western Himalayas. Water samples were collected from two glaciated catchments (Lato and Stok), Chabe Nama (tributary) and the Indus River in Ladakh. The mildly alkaline pH (range 7.3-8.5) and fluctuating ionic trend of the meltwater samples reflected the distinct geology and weathering patterns of the Upper Indus Basin (UIB). Gibbs plot and mixing diagram revealed rock weathering outweighed evaporation and precipitation. The strong associations between Ca2+-HCO3-, Mg2+-HCO3-, Ca2+-Mg2+, Na+-HCO3-, and Mg2+-Na+ demonstrated carbonate rock weathering contributed to the major ion influx. Principal component analysis (PCA) marked carbonate and silicates as the most abundant minerals respectively. Chemical weathering patterns were predominantly controlled by percentage of glacierized area and basin runoff. Thus, Lato with the larger glacierized area (~ 25%) and higher runoff contributed low TDS, HCO3-, Ca2+, and Na+ and exhibited higher chemical weathering, whereas lower chemical weathering was evinced at Stok with the smaller glacierized area (~ 5%). In contrast, the carbonate weathering rate (CWR) of larger glacierized catchments (Lato) exhibits higher average value of 15.7 t/km2/year as compared to smaller glacierized catchment (Stok) with lower average value 6.69 t/km2/year. However, CWR is high in both the catchments compared to silicate weathering rate (SWR). For the first time, in situ datasets for stream water chemical characteristics have been generated for Lato and Stok glaciated catchments in Ladakh, to facilitate healthy ecosystems and livelihoods in the UIB.

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In many high altitude river basins, the hydro-climatic regimes and the spatial and temporal distribution of precipitation are little known, complicating efforts to quantify current and future water availability. Scarce, or non-existent, gauged observations at high altitudes coupled with complex weather systems and orographic effects further prevent a realistic and comprehensive assessment of precipitation. Quantifying the contribution from seasonal snow and glacier melt to the river runoff for a high altitude, melt dependent region is especially difficult. Global scale precipitation products, in combination with precipitation-runoff modelling may provide insights to the hydro-climatic regimes for such data scarce regions. In this study two global precipitation products; the high resolution (0.1°â€¯× 0.1°), newly developed ERA5-Land, and a coarser resolution (0.55°â€¯× 0.55°) JRA-55, are used to simulate snow/glacier melts and runoff for the Gilgit Basin, a sub-basin of the Indus. A hydrological precipitation-runoff model, the Distance Distribution Dynamics (DDD), requires minimum input data and was developed for snow dominated catchments. The mean of total annual precipitation from 1995 to 2010 data was estimated at 888 mm and 951 mm by ERA5-Land and JRA-55, respectively. The daily runoff simulation obtained a Kling Gupta efficiency (KGE) of 0.78 and 0.72 with ERA5-Land and JRA-55 based simulations, respectively. The simulated snow cover area (SCA) was validated using MODIS SCA and the results are quite promising on daily, monthly and annual scales. Our result showed an overall contribution to the river flow as about 26% from rainfall, 37-38% from snow melt, 31% from glacier melt and 5% from soil moisture. These melt simulations are in good agreement with the overall hydro-climatic regimes and seasonality of the area. The proxy energy balance approach in the DDD model, used to estimate snow melt and evapotranspiration, showed robust behaviour and potential for being employed in data poor basins.

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Water resources are under severe stress in the highly populated Indus River Basin due to the increased consumption of water across different sectors and climate change. Coping with these challenges, requires a clear understanding on hydrological processes and anthropogenic activities, and how these are influencing recharging and spatiotemporal availability of groundwater in the basin. The present study aims to investigate the natural and anthropogenic impact on Terrestrial Water Storage (TWS) over the Indus River Basin by using a series of statistical methods and the observation data from the Gravity Recovery and Climate Experiment (GRACE) and Follow-On (GRACE-FO). Our results show that (i) TWS Anomaly (TWSA) experienced a significant decrease from 2002 to 2020, particularly in the MUIP; (ii) the UIB showed a weak decreasing trend in TWSA as a result of the accelerated glacier melting; (iii) there was significant loss of groundwater (1.57 mm/month) caused by ineffective water management and over-exploitation; and (iv) assisted by favorable meteorological conditions, the precipitation presented a positive trend against the weakness of the Westerlies, which exerted the positive influence on TWSA.

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There is research evidence that due to global warming, global precipitation and monsoon area have shown a shift which needs to be analyzed at regional scale. This study analyses future precipitation and monsoon spatial shift over Pakistan and Upper Indus Basin (UIB) based on latest Coordinated Regional Climate Downscaling Experiment - Coordinated Output for Regional Evaluations (CORDEX-CORE) high resolution projections (25 km) for the South Asian domain. Three global climate models from Coupled Model Intercomparison Project Phase 5 (CMIP5) (MIROC5, NorESM1-M and MPI-ESM-MR) provided the lateral boundary conditions for the Regional Climate Model (RegCM4) under Representative Concentration Pathways 2.6 (RCP2.6) and RCP8.5 scenarios. Results indicate that JJA precipitation over Upper Indus Basin (UIB which also includes North Pakistan) is projected to increase more under RCP8.5 and less under RCP2.6 while for Pakistan it shows slightly increase (decrease) in RCP2.6 (RCP8.5). The results also show a projected expansion in monsoon area in UIB and northward shift of MCR which corresponds with future precipitation changes in the area and hence indicate the penetration of monsoon system over UIB under higher warming scenario. The changes in monsoon precipitation and domain are related to the changes in wind circulation patterns at 850 hPa and 200 hPa atmospheric levels.

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We analyse an ensemble of statistically downscaled Global Climate Models (GCMs) to investigate future water availability in the Upper Indus Basin (UIB) of Pakistan for the time horizons when the global and/or regional warming levels cross Paris Agreement (PA) targets. The GCMs data is obtained from the 5th Phase of Coupled Model Inter-Comparison Project under two Representative Concentration Pathways (RCP4.5 and RCP8.5). Based on the five best performing GCMs, we note that global 1.5 °C and 2.0 °C warming thresholds are projected in 2026 and 2047 under RCP4.5 and 2022 and 3036 under RCP8.5 respectively while these thresholds are reached much earlier over Pakistan i.e. 2016 and 2030 under RCP4.5 and 2012 and 2025 under RCP8.5 respectively. Interestingly, the GCMs with the earliest emergence at the global scale are not necessarily the ones with the earliest emergence over Pakistan, highlighting spatial non-linearity in GCMs response. The emergence of 2.0 °C warming at global scale across 5 GCMs ranges from 2031 (CCSM4) to 2049 (NorESM) under RCP8.5. Precipitation generally exhibits a progressive increasing trend with stronger changes at higher warming or radiative forcing levels. Hydrological simulations representing the historical, 1.5 °C and 2.0 °C global and region warming time horizons indicate a robust but seasonally varying increase in the inflows. The highest inflows in the baseline and future are witnessed in July. However, the highest future increase in inflows is projected in October under RCP4.5 (37.99% and 65.11% at 1.5 °C and 2.0 °C) and in April under RCP8.5 (37% and 62.05% at 1.5 °C and 2.0 °C). These hydrological changes are driven by increases in the snow and glacial melt contribution, which are more pronounced at 2.0 °C warming level. These findings should help for effective water management in Pakistan over the coming decades.

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Contemporary changes in the Himalayan cryosphere are an important concern in the global climate change debate. In this context, the glaciers of the Upper Indus Basin (UIB) deserve special attention because of their importance for freshwater supply in the mountain valleys and the adjoining lowlands. However, detailed long-term glacier monitoring studies are rare due to the lack of historical data with adequate spatial and temporal resolution. In the case of Nanga Parbat, the ample availability of historical maps and terrestrial photographs together with satellite imagery and digital elevation models make it possible to analyse and quantify glacier changes for the period between 1856 and 2020. Using diverse multi-temporal datasets, this study reveals slight changes in ice-covered area for 63 glaciers, which decreased by 7% between 1934 and 2019. A detailed analysis of five glaciers in the Rupal Valley over the period 1856-2020 identifies diverse response patterns and highlights the importance of ice and snow avalanches, surge-type instabilities and site-specific topographic particularities for individual glacier changes. The results show high similarity with the stable glacier mass in the Karakoram. This study demonstrates the advantages of combining multiple sources and types of data in order to achieve consilience and offer robust insights.

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Water availability is important for survival of millions of people living in the Himalayan region of Upper Indus Basin and adequate monitoring system is for better water resources management. In the present study, groundwater recharge appraisals in the Neelum watershed (Upper Indus Basin) were investigated by using water balance and geospatial modeling techniques on monthly time-scale climate data from 1989 to 2015. Results demonstrated that on an average out of total annual rainfall (i.e., 2028 mm), about 46% of the rainfall convert to surface runoff and 35% loss to atmosphere via evapo-transpiration (ET), while the remaining 18% contribute to infiltrate the groundwater recharge. Groundwater recharge enhanced during snow-melt from December to March and the rainfall infiltration increased during July and August months. Similarly, the infiltration ranges 106-177 mm from January to March and 45-51 mm from December to July. The groundwater discharge in the form of oozing from the spring occurred during the remaining six months, which ultimately contributed to the baseflow of the stream. Findings from the study revealed variations in groundwater recharge during the years and hence recommended more hydrological studies to predict future changes in climate and land use for sustainable development of freshwater resources in the Upper Indus Basin.

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The Upper Indus Basin (UIB), which covers a wide range of climatic and topographic settings, provides an ideal venue to explore the relationship between climate and topography. While the distribution of snow and glaciers is spatially and temporally heterogeneous, there exist regions with similar elevation-snow relationships. In this work, we construct elevation-binned snow-cover statistics to analyze 3415 watersheds and 7357 glaciers in the UIB region. We group both glaciers and watersheds using a hierarchical clustering approach and find that (1) watershed clusters mirror large-scale moisture transport patterns and (2) are highly dependent on median watershed elevation. (3) Glacier clusters are spatially heterogeneous and are less strongly controlled by elevation, but rather by local topographic parameters that modify solar insolation. Our clustering approach allows us to clearly define self-similar snow-topographic regions. Eastern watersheds in the UIB show a steep snow cover-elevation relationship whereas watersheds in the central and western UIB have moderately sloped relationships, but cluster in distinct groups. We highlight this snow-cover-topographic transition zone and argue that these watersheds have different hydrologic responses than other regions. Our hierarchical clustering approach provides a potential new framework to use in defining climatic zones in the cyrosphere based on empirical data.

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In the semi-arid high mountains of the Upper Indus Basin (UIB), meltwater supply from the cryosphere is vital for irrigated agriculture and hydropower generation. An overlooked cryosphere component that is critical for this is aufeis, which appears as a sheet-like formation of ice layers, created by successive and laminated freezing of flowing water. This study aims to redress the lack of knowledge about this phenomenon by creating an inventory of aufeis fields for the UIB and analysing their spatial distribution, including the role of topographical parameters such as altitude, slope, and aspect. The study is based on a time-series analysis using Landsat imagery from 2010 to 2020, supported and validated by several field campaigns carried out between 2014 and 2020. In total, more than 3700 aufeis fields were detected covering an area of about 298 ± 38 km2. The spatial distribution of their occurrence indicates a distinct elevation range between 4000 and 5500 m a.s.l. and is marked by a pronounced longitudinal increase to the east. In contrast to the western part of the UIB (Gilgit-Baltistan), where only some few and small aufeis fields can be detected, 65% of the aufeis covered areas (195 ± 23 km2) exist on the Tibetan Plateau. Our database fills an important research gap and will help in further cryosphere studies in the UIB and beyond.

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Melting of snow and glaciers from the high-altitude Himalayan region is a significant water source to the major Himalayan rivers, especially in the upper Indus Basin (UIB), which contributes up to 70% of river discharge. Considering Indus Basin as a largest irrigation system dependent on snow and glacier melt runoff, it is imperative to study the rivers' current status and water budget. In this study we have performed a tracer-based hydrograph separation to quantify the contribution of seasonal snow, glacier melt, and groundwater to the Chandra River draining from a semi-arid region of the upper Indus basin, western Himalaya. Our study revealed a negligible control of summer (May-September 2017) precipitation and significant control of summer air temperature (May-September 2017) and winter precipitation over the Chandra River discharge, with 1 °C rise in air temperature leading to 22 m3s-1 (15% of mean) increase in the river discharge (R2 = 0.85; n = 541; p < 0.001). The hydrograph separation of the Chandra River suggests groundwater (38.3 ± 5.6%; 96.8 m3s-1) as a significant source to the river runoff, followed by a direct contribution from glacier melt (30.9 ± 9%; 88.2 m3s-1) and seasonal snowmelt (30.6 ± 5.7%; 84.2 m3s-1), respectively, with negligible contribution from rainfall. Although groundwater is a significant contributor to the river runoff, the infiltration of seasonal snowmelt (54%) and glacier melt (46%) mostly contributed to the groundwater recharge. Present study establishes a linkage between seasonal snowmelt, glacier melt, groundwater, and the river runoff and would be useful to better model and predicts the future changes in the water resources of the upper Indus Basin.

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Pakistan is highly dependent on water resources from the mountainous regions of the Upper Indus Basin (UIB), especially for irrigation. An evaluation framework was developed and applied in this study to understand the variability in surface water availability to agricultural and domestic sectors across various future climate and socioeconomic pathways in five catchments within the UIB (Astore, Gilgit, Hunza, Shigar, and Shyoke). A planning tool named Water Evaluation and Planning (WEAP) was used to understand the dynamics of past and future water demands for multiple future scenarios. We combined three different climate scenarios (representative concentration pathways) with socioeconomic scenarios (shared socioeconomic pathways) of economic development and population and local agricultural land development pathways. The results indicate that the external driving forces of climate change and socioeconomic growth will cause a discrepancy between the supply and demand of water resources in regions with higher socioeconomic growth, particularly those with agricultural development as the dominant external factor. Among the five catchments within the UIB, Astore and Gilgit face a water shortfall in all future scenarios, whereas Shyoke will encounter water deficiencies only in the case of agricultural land development. We also demonstrated that the impact of climate change is markedly different in Astore and Gilgit. Over Astore, the impact of precipitation will control the unmet water demands by increasing winter streamflow whereas over Gilgit non-climatic factors, such as population and agricultural growth, will control future unmet water demands.

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Glacier runoff shows significant change under global warming in the headwater region of the Indus River with great impact on its highly populated downstream area, but the hydrochemistry characteristics of meltwater and the changing mechanism remain unclear in this region. In this study, runoff water samples were collected during May and June, 2015, from four glacial catchments in the Upper Indus Basin to investigate general characteristics and daytime dynamics of meltwater runoff together with sediment and chemical contents. Results showed that glacier runoff in the studied area had an alkaline pH and much higher sediment yields than the local average of the non-glacier areas. The carbonate-dominated geological feature in the four catchments resulted in single chemical facies of Ca-HCO3. The dominant process determining the glacier runoff chemistry was rock-water interaction, with less soluble minerals and less intensive evaporate weathering in the Passu and Gulmit catchments than the B&B and Hinarchi catchments. Comparing the investigated catchments, the larger glacier with longer flow path exhibited higher runoff but lower melting rate, higher SSC resulting from higher erosive power of flow, and higher solute concentrations as a consequence of more intensive contact of meltwater with rock minerals along the longer flow path. For individual catchments, a negative correlation between TDS and flow rate (R2 = 0.26~0.53) and changing trends of ion ratios with flow rate demonstrated that under intensive melting conditions, rock-water interactions were reduced, resulting in dilution of solutes. Overall, the general chemical characteristics of the investigated glacier runoff indicated geological control, whereas individual glacier illustrated hydrological control on the daytime dynamics of glacier runoff chemistry. The presence of glacier terminal lake and agriculture land can significantly alter the hydrochemistry of downstream runoff.

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The Indus River, the lifeline of Pakistan's economy and its tributaries, derives most of water flow from the upper Indus basin comprised of Karakorum, Himalaya, and Hindu Kush mountain ranges, thus making this area important in climate change studies. We analyzed the records of climatic variables including temperature, precipitation, and relative humidity (RH) from two weather stations (Gilgit and Skardu) of upper Indus basin region from 1953 to 2006. To observe the trends of climate change, the selected time was divided into two temporal half periods consisting of 27 years each (1953-1979 and 1980-2006). The overall mean temperature (OMT) was decreased by - 0.137 °C in Gilgit, while an increase of 0.63 °C was observed in Skardu during the later period compared to the previous one. The mean minimum temperature (MMT) was found to decrease while mean maximum temperature (MXT) showed non-significant changes during the summer at both locations. However, there was an evidence of spring and winter warming at both locations due to increase in the MXT. The precipitation data showed large interannual variation at both locations. Significant increases in the morning relative humidity (RH) were observed during summer and autumn months at Skardu and throughout the year at Gilgit, while the evening RH increased during the same seasons at both stations. Significant increase in MXT and OMT during spring and winter months at higher elevation (Skardu) may have serious implications for the deposition and melting of seasonal snowpack with impacts on local livelihoods and river flow.

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