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The Himalayan water tower provides crucial water resources for Asia. Permafrost degradation is deemed to exert important impacts on streamflow in the Himalayan rivers. Yet, the magnitudes of such impacts remain poorly quantified. Here, we established a robust hydrological model that incorporated active layer deepening and ground ice melt for the drainage basin of the largest river in the northern Himalayas-the Yarlung Zangbo River (YZR). We estimated that permafrost degradation led to ∼0.65 km3/yr decrease in surface runoff and ∼0.35 km3/yr increase in baseflow and ground ice melt contributed ∼0.25% to the annual streamflow in the YZR for the period 2001–2022. The "fill-and-spill" mechanism helps explain the seeming contradiction of observed increasing versus decreasing baseflow in different permafrost regions worldwide. We propose that the dilution of riverine dissolved organic carbon (DOC) concentrations by baseflow may lead to the riverine DOC hysteresis patterns. This study not only lays solid scientific basis for water resources management in the Himalayas, but also yields new insights into how to interpret measured river discharge and nutrient flux in permafrost regions over the globe. [ABSTRACT FROM AUTHOR]

Atmospheric rivers (ARs) have the potential to generate large-impact hydrometeorological events over mountainous topography. In this study, we investigate ARs' impacts on the hydrology of Indus basin (IB) and Ganga basin (GB), two highly populated basins of the Himalayas. We used the recently developed 37-yr-long ERA5-based AR database over the Himalayas to explore the influence of ARs on total and extreme precipitation, snowfall, and floods over these basins. We find that ARs contribute ∼25% to the annual rainfall in the IB and ∼15% in the GB. Over the mountainous regions, ARs contribute more than 50% to winter precipitation in Karakoram (KA), Hindu–Kush (HK), central (CH), and western Himalayas (WH), and respectively explain over 75%, 57%, 42%, and 30% of their interannual variability. The seasonal rainfall extremes over the mountain foothills are most often (50%–100%) associated with ARs in winter and spring, whereas the summer and autumn extremes over the plains and mountains foothills appear moderately associated with ARs (10%–40%). The two most catastrophic flood events (2014 Kashmir flood and 2013 Uttarakhand flood) in these basins are found to be linked with category 5 ARs. Upon further examination of floods over a long period, we noted that 56% and 73% of the floods in IB and GB, respectively, are related to ARs. Thus, our results establish that the variance of ARs is a major source of hydroclimate variability in the two Himalayan basins. [ABSTRACT FROM AUTHOR]

Considering the sensitivity and importance of water resources in the Himalayan uplands, this study intended to assess the hydrological responses to climate change in the Jhelum basin. Representative concentration pathway (RCP)–based projections from six dynamically downscaled global circulation models (GCMs) were bias-corrected for developing the climatic projections over the twenty-first century. The uncertainty associated with GCM outputs was addressed by using multi-model ensemble projections developed through Bayesian model averaging (BMA) technique. The assessment reveals that compared to the baseline (1980–2010) values, the annual mean maximum temperature in the basin will rise by 0.41–2.31 °C and 0.63–4.82 °C, and the mean minimum temperature will increase by 1.39–2.37 °C and 2.14–4.34 °C under RCP4.5 and RCP8.5, respectively. While precipitation is expected to decrease by 7.2–4.57% and 4.75–2.47% under RCP4.5 and RCP8.5, correspondingly. BMA ensemble projections were coupled with the Soil and Water Assessment Tool (SWAT) to simulate the future hydrological scenarios of the drainage basin. With the changing climate, the discharge of rivers in the Jhelum basin is expected to witness reductions by about 23–37% for RCP4.5 and 19–46% for RCP8.5. Moreover, the water yield of the basin may also exhibit decreases of 17–25% for RCP4.5 and 18–42% for RCP8.5. The projected scenarios are likely to cause water stress, affect the availability of water for diverse uses, and trigger transboundary water-sharing-related conflicts. The impact of climate change on discharge demands early attention for the formulation of mitigation and adaptive measures at the regional level and beyond. [ABSTRACT FROM AUTHOR]

The hydrology of Himalayan region is influenced by temperature lapse rate (TLAPS) and precipitation lapse rate (PLAPS). Therefore, hydrological modeling considering TLAPS and PLAPS is crucial to manage the water resources in these terrains. In this research, Himalayan Gandak River basin is considered as the study area where TLAPS and PLAPS vary significantly due to high altitude of Himalayas. To assess the impact of TLAPS and PLAPS on water balance components, Soil Water Assessment Tool (SWAT) model was calibrated (2000–2007) and validated (2008–2014) on daily time step for three projects i.e., Reference Project (RP), Snowmelt Project (SP) and distributed elevation band snowmelt project (SWAT-ETISM). The analysis discloses that SWAT-ETISM model (which has TLAPS and PLAPS parameters) outperforms the RP and the SP models in predicting streamflow with improved statistical indicators R2 =0.88, NSE =0.84 and PBIAS = 11.9. Furthermore, it was observed that SWAT-ETISM model comprehensively improved the streamflow statistics by improving the snow water equivalent and water balance components through the consideration of TLAPS and PLAPS values for the region. Hence, the proposed SWAT-ETISM model can be used for estimation of the water budget at the high-altitude and data scarce alpine Himalayan regions and worldwide, where PLAPS and TLAPS are substantial due to altitudinal variation. [ABSTRACT FROM AUTHOR]

The Indian Summer Monsoon (ISM) characterizes the hydrometeorological variability across the north Indian region and contributes more than 75% of the annual rainfall during the monsoon (June–September) season. In the present study, we analysed the long-term monsoon rainfall for the Ganga River basin to investigate its spatio-temporal variability. A statistically increasing (10 to 17 mm/year; p < 0.05) trend has been observed in ISM rainfall for the mountainous region since 1980, accompanied by increased temperature. We further note that high, very high and extreme rainfall events are also increasing, enhancing the flash flood risk in the mountainous region. In contrast, the ISM rainfall in the alluvial region is observed to be statistically decreasing (−5 to −20 mm/year; p < 0.05) with the combined influence of reduced vegetation. These findings provide valuable insights into the variations in regional hydrology of the Ganga River basin caused by natural and anthropogenic factors. [ABSTRACT FROM AUTHOR]

Precipitation over the southern rim of the Indian Himalayan Region (IHR) mainly occurs due to two dominant synoptic weather systems: Indian winter (IWM: December, January, February) and summer monsoon (ISM: June, July, August, September). The genesis and evolution of these systems are extensively researched. Additionally, geographical location, season, orography controls the strengths of these systems along and across the southern rim of the IHR. However, plausible positioning of the frontal threshold limit of precipitation during IWM and ISM over the IHR remains an elusive scientific question. Thus, with the help of water samples collected in the upper Bhilangana River Basin (BRB in the central Himalayas), an attempt has been made to assess this frontal threshold limit of precipitation and is defined as "quasi monsoon front (QMF)" in the IHR. Results show depleted (enriched) stable water isotopic values at higher (lower) altitudes suggesting an elevation control. The intercepts of local meteoric water lines (LMWLs) of glacier ice/glacier melt (2.5), snow packs/snow melt (7.7), and stream water (10.3) reflect mixing of precipitation due to IWM and ISM. The d-excess values in water samples lie between the d-excess value of a typical IWM (~20‰) and ISM (~10‰), suggesting mixing of moisture from both Atlantic ocean – Mediterranean sea and Indian ocean-Bay of Bengal-Arabian sea. The tracer based hydrographic analysis indicates dominance of snow melt contributions to the regional hydrology. Hybrid Single Particle Lagrangian Integrated Trajectory Model (HYSPLIT) model in the back trajectory mode estimates moisture sources of the IWM and ISM. Based on precipitation isotopic composition and associated moisture source regions, QMF oscillates in the northwest and southeast direction of the IHR depending on the strength and/or weakness of IWM and ISM. This work hypothesizes for upscale determination and description of the pulsatory extension of QMF in the central Himalayas (along BRB). [ABSTRACT FROM AUTHOR]

Himalayan rivers originating generally from >4000 masl, sustain large number of population downstream. However, these river basins are highly data scarce, and in situ data for hydro-meteorological parameters is available mainly from the regions below 2000 masl. Considering the high level of human dependence on these rivers, it is important to develop policies and plans based on the hydrology of these rivers. Thus it is important to quantify the contribution of various runoff components like snow and ice melt, baseflow, etc. This paper has used conceptual hydrological model, HBV model to estimate the composition and contribution of various runoff components, for the Chenab river basin, Western Himalayas. Similar to hydrological modelling results for other basins of western Himalayas, this study shows that snow and ice melt contribution is significant in the basin and ranges between 40–66% of the total runoff in different seasons. During the post monsoon period, baseflow sustains the perennial nature of river. This research attempts to quantify the seasonal contributions to river runoff and provides valuable insights into hydrological processes operating in this high altitude hydrological catchment to facilitate improved management of water resources in the basin. The study further outlines the uncertainty in simulating low flows in ungauged catchments being fed by snow/ice melt. [ABSTRACT FROM AUTHOR]

Discharge over the Narayani river catchment of Nepal was simulated using Statkraft's Hydrologic Forecasting Toolbox (Shyft) forced with observations and three global forcing datasets: (i) ERAInterim (ERA-I), (ii) Water and Global Change (WATCH) Forcing Data ERA-I (WFDEI), and (iii) Coordinated Regional Climate Downscaling Experiment with the contributing institute Rossy Centre, Swedish Meteorological and Hydrological Institute (CORDEX-SMHI). Not only does this provide an opportunity to evaluate discharge variability and uncertainty resulting from different forcing data but also it demonstrates the capability and potential of using these global datasets in data-sparse regions. The fidelity of discharge simulation is the greatest when using observations combined with the WFDEI forcing dataset (hybrid datasets). These results demonstrate the successful application of global forcing datasets for regional catchment-scale modeling in remote regions. The results were also promising to provide insight of the interannual variability in discharge. This study showed that while large biases in precipitation can be reduced by applying a precipitation correction factor (p_corr_factor), the best result is obtained using bias-corrected forcing data as input, i.e. the WFDEI outperformed other forcing datasets. Accordingly, the WFDEI forcing dataset holds great potential for improving our understanding of the hydrology of data-sparse Himalayan regions and providing the potential for prediction. The use of CORDEX-SMHI- and ERA-I-derived data requires further validation and bias correction, particularly over the high mountain regions. [ABSTRACT FROM AUTHOR]

• Three-endmember δ18O-d-excess mixing model has been developed. • Deterministic Monte Carlo is used to develop the model. • The model can quantify the contribution from different sources. • The mean glacial ice-melt contribution is between 40 and 47% in different seasons. The glaciated Himalayan region is the third largest storehouse of freshwater in its frozen form that feeds several mega river systems. Especially the north-eastern Himalayas, where the snow and glacial stock depend on various moisture sources. This study presents a detailed investigation of water sources in the Teesta watershed in terms of oxygen (δ18O) and deuterium (δD/δ2H) values. The study helped understand the Spatio-temporal variability in the isotopic composition of water and moisture sources. Progressive depletion of δ18O values in the stream water as moving towards the non-renewable glacial source indicates orographic ascent attributed to cooling and subsequent rainout. This effect is profound in the case of the western tributary above Chungthang, the Lachen Chu river. The computed d-excess values suggest the dominance of mid-latitude westerlies in the high-altitude perennial streams of the west and north Sikkim. Also, a deterministic Monte Carlo-based three endmember δ18O-d-excess mixing model is developed to quantify the contribution of source endmembers such as snowmelt, rainfall, and glacial melt in the river streams and waterfalls of the Rathong river as well as Lachen Chu and Lachung Chu rivers above their confluence at Chungthang. With the model being iterated 10,000 times for each waterfall and stream sample, the results have been obtained at the mean, 25th, 75th and 95th percentiles. The model results in the mean glacial ice-melt contribution between 40% and 47% in different seasons, with the standard deviation between ± 3.5% and ± 10%. [ABSTRACT FROM AUTHOR]

Abstract: Soil moisture dynamics have a significant effect on overland flow generation. Catchment aspect is one of the major controlling factors of overland flow and soil moisture behaviour. A few experimental studies have been carried out in the uneven topography of the Himalayas. This study presents plot‐scale experiments using portable rainfall simulator at an altitude of 1,230 m above mean sea level and modelling of overland flow using observed datasets. Two plots were selected in 2 different aspects of Aglar watershed of Lesser Himalaya; the agro‐forested (AF) plot was positioned at the north aspect whereas the degraded (DE) plot was located at the south aspect of the hillslope. HS flumes and rain gauges were installed to measure the runoff at the outlet of the plot and the rainfall depth during rainfall simulation experiments. Moreover, 10 soil moisture sensors were installed at upslope and downslope locations of both the plots at 5, 15, 25, 35, and 45 cm depth from ground level to capture the soil moisture dynamics. The tests were conducted at intensities of 79.8 and 75 mm/hr in AF plot and 82.2 and 72 mm/hr in the DE plot during Test 1 and Test 2, respectively. The observed data indicate the presence of reinfiltration process only in the AF plot. The high water holding capacity and the presence of reinfiltration process results in less runoff volume in the AF plot compared with the DE plot. The Hortonian overland flow mechanism was found to be the dominant overland flow mechanism as only a few layers of top soil get saturated during all of the rainfall–runoff experiments. The runoff, rainfall, and soil moisture data were subsequently used to calibrate the parameters of HYDRUS‐2D overland flow module to simulate the runoff hydrograph and soil moisture. The components of hydrograph were evaluated in terms of peak discharge, runoff volume and time of concentration, the results were found to be within the satisfactory range. The goodness of fit of simulated hydrographs were more than 0.85 and 0.95 for AF and DE plot, respectively. The model produced satisfactory simulation results of soil moisture for all of the rainfall–runoff experiments. The HYDRUS‐2D overland flow module was found promising to simulate the runoff hydrograph and soil moisture in plot‐scale research. [ABSTRACT FROM AUTHOR]

The impact of increased temperature on the Third Pole, as the Himalayas is referred to, and the likely cascading impacts on the general downstream hydrology have been widely noted. However, the impact on fluvial geomorphology has not received specific attention. Change in the glacial domain in terms of melt increase will change discharge and sediment flux into fluvial system, which will induce changes in fluvial processes and forms. The present work attempts to study this process-based glacio-fluvial coupling in the two neighbouring glaciated river basins in the Northwest Himalaya, viz., the Sutlej and the Yamuna river basins till the mountain front. A total of 194 samples of river, tributary and groundwater of pre- and post-monsoon seasons in the two river basins were analysed for stable isotopes. The trend of δO and electrical conductivity along the mainstream gives qualitative idea on the influence of headwaters in the downstream of the catchment thereby allowing inference on melt contribution. Further, two component mixing model using stable oxygen isotope of two seasons water samples showed that melt contributes about 41.1-66.8 and 6.6-10.6% at different points to the total river discharge in the Sutlej and the Tons River (the glaciated, major tributary of the Yamuna River) basins, respectively. For different scenarios of increase in melt, stream power increase in the Sutlej River basin is significant as opposed to the Tons River. River channel in the Sutlej River basin will be significantly more impacted in comparison with the Yamuna River system. [ABSTRACT FROM AUTHOR]

In a changing climate, river basins with limited summer precipitation but abundant snow and glacier melt-water are affected severely by reductions and seasonal alterations in annual stream flows. However, high altitude glacio-hydrological observations and investigations to address the linkage between the timing of glacier changes and river runoff fluctuations remain ambiguous, particularly in the northwestern Himalayan region of Pakistan. In this context, the hydrological regime of the Astore Basin, a sub-catchment of the Upper Indus River Basin, was comprehensively investigated by employing in situ hydro-meteorological observations in combination with satellite remote sensing data. Two-thirds of the annual precipitation in the Astore Basin falls in winter and spring, mainly deposited by westerly winds, whereas summer and autumn precipitation deposited by the monsoon and local jet streams accounts for only one-third. Some 14 % of the basin area is covered by glaciers and, added to the accumulated seasonal snow deposited by westerly circulations, this can reach 80-85 % of the basin area. Therefore more than 75 % of the annual basin runoff depends on melt-water produced by the predominant seasonal snow and glacier ablation. The non-parametric Mann-Kendall trend test was applied to the whole time-series of hydro-meteorological data. This indicated a lowering of annual and summer mean temperatures during the period 1980-1995 and slight warming during the 1996-2010 period. Similarly, annual, winter and summer precipitation, and annual mean discharge, increased from 1980 to 1995 but, in contrast, a slight decrease in annual and summer precipitation was observed during the 1996-2010 period; however, discharge evidence is slight making any increase in this period insignificant. In addition, the Spearman and Mann-Kendall correlation results depict annual stream flow fluctuations during the 1980-2010 decades in the Astore River that were predominantly influenced by precipitation variations, but not by any alteration in catchment temperatures, and so not governed by enhanced glacier ablation and retreat. The results of the analysis presented here were also substantiated by satellite remote sensing investigation, which points to evidence of stable conditions in the Astore Basin glaciers during this period. [ABSTRACT FROM AUTHOR]

Snow is an essential resource present in the Himalaya. Therefore, monitoring of the snowfall changes over a time period is important for hydrological and climatological purposes. In this study, variability of snowfall from 1976-2008 were analysed and compared with variability in temperature ( T and T) from 1984-2008 using simple linear regression analysis and Mann-Kendall test in the Satluj Basin. The annual, seasonal, and monthly analyses of average values of snowfall and temperature ( T and T) have been carried out. The study also consists an analysis of average values of annual snowfall and temperature over six elevation zones (<1500 to >4000 m amsl). During the study, it was observed that the snowfall exhibited declining trends in the basin. The snowfall trends are more sensitive to the climate change below an elevation of 4000 m amsl. Over the elevation zones of 3000-3500 and 4000-4500 m amsl, positive trends of mean annual values of snowfall were observed that may be due to higher precipitation as snowfall at these higher elevations. Although, both negative and positive snowfall trends were statistically insignificant, however, if this decreasing trend in snowfall continues, it may result in significant however, changes in future. Furthermore, the T is also increasing with statistically significant positive trend at 95% confidence level for November, winter season, annually as well as for the elevation zones of 2500-3000, 3000-3500, and 3500-4000 m amsl. There are dominantly increasing trends in T with negative trends for February, June-September, monsoon season, and for elevation zone <1500 m amls. It is important to state that in the present basin, during the months of winter season, most of the precipitation is produced as snowfall by the westerly weather disturbances. Thus, the declining nature in snowfall is concurrent with the positive trends in temperature particularly T, therefore, reflecting that the positive trends in T may be the dominant factor besides T in controlling the snowfall trends. The snowfall data were also compared with SCA and this showed a highly positive correlation of 0.95% which validates the utilisation of time series of snowfall for the trend analysis. [ABSTRACT FROM AUTHOR]

In this paper, we evaluate the impact of changing land use/land cover (LULC) on the hydrological processes in Dal lake catchment of Kashmir Himalayas by integrating remote sensing, simulation modelling and extensive field observations. Over the years, various anthropogenic pressures in the lake catchment have significantly altered the land system, impairing, inter-alia, sustained biotic communities and water quality of the lake. The primary objective of this paper was to help a better understanding of the LULC change, its driving forces and the overall impact on the hydrological response patterns. Multi-sensor and multi-temporal satellite data for 1992 and 2005 was used for determining the spatio-temporal dynamics of the lake catchment. Geographic Information System (GIS) based simulation model namely Generalized Watershed Loading Function (GWLF) was used to model the hydrological processes under the LULC conditions. We discuss spatio-temporal variations in LULC and identify factors contributing to these variations and analyze the corresponding impacts of the change on the hydrological processes like runoff, erosion and sedimentation. The simulated results on the hydrological responses reveal that depletion of the vegetation cover in the study area and increase in impervious and bare surface cover due to anthropogenic interventions are the primary reasons for the increased runoff, erosion and sediment discharges in the Dal lake catchment. This study concludes that LULC change in the catchment is a major concern that has disrupted the ecological stability and functioning of the Dal lake ecosystem. [ABSTRACT FROM AUTHOR]

Summary: The spatial and temporal distribution of δ18O and δD measurements of precipitation and stream waters were used to distinguish various sources and components of stream flow and to estimate their residence times in snow dominated mountainous catchments of Kashmir Himalaya. A marked spatial and seasonal variability of stable isotopes of oxygen and hydrogen was observed in precipitation with δ18O and δD varied from −12.98‰ to −0.58‰ and −74.5‰ to −11.1‰, respectively during the period from November 2007 to January 2009. The seasonal changes in stable isotopes of precipitation with depleted and enriched 18O and 2H in January/March/May and July/September/November, respectively at each site are attributed to the seasonal changes in ambient temperature, precipitation, source of moisture and airmass trajectory. The mean altitude effect of −0.23‰ and −1.2‰ per 100m change in elevation for δ18O and δD, respectively, was observed based on amount weighted mean precipitation isotopic composition data. Unlike precipitation, less variability of stable isotopes of streams was found with δ18O and δD ranging from −11.56‰ to −6.26‰ and −65.4‰ to −36.4‰, respectively, the depleted values being observed in the headwaters of the streams/tributaries and enriched values at lower elevations of the watersheds. The LMWL established for the Kashmir Himalayas, based on amount weighted monthly samples is δD=7.59 (±0.32)×δ18O+11.79 (±2.07) (r 2 =0.96) with lower slope and intercept than GMWL, is very close to the LMWL for the western Himalayas. The seasonal regression lines suggest the effect of evaporation with lower slopes and intercepts except in winter. The results suggest that the winter precipitation (snow) dominantly contributes the annual stream flow with average snowmelt contribution of about 29% in early spring, 66% in late spring, 61% in summer while the baseflow contribution is found in the order of 40% in autumn season. The mean stream residence times (MRTs) varied from 6 to 12.4months. The longer MRT of the Liddar catchment is attributed to its complex topography and larger area. [Copyright &y& Elsevier]

Abstract: We present an analysis of daily water discharge and suspended sediment concentration measurements for the three main drainage basins in Nepal, on the basis of recent published papers. We first show how precipitation-discharge data can be used to highlight the impact of groundwater storage on the annual hydrological cycle of Himalayan rivers. Then, we show how the concentration of suspended sediment in rivers varies at the year scale depending on the river discharge cycle, as well as how the release of groundwater impacts the concentration of materials in rivers. Finally, we propose a new conceptual model for the mobilization and transportation of material within the monsoonal discharge cycle in the central Himalayas. [Copyright &y& Elsevier]

The analysis of climate change impact on the hydrology of high altitude glacierized catchments in the Himalayas is complex due to the high variability in climate, lack of data, large uncertainties in climate change projection and uncertainty about the response of glaciers. Therefore a high resolution combined cryospheric hydrological model was developed and calibrated that explicitly simulates glacier evolution and all major hydrological processes. The model was used to assess the future development of the glaciers and the runoff using an ensemble of downscaled climate model data in the Langtang catchment in Nepal. The analysis shows that both temperature and precipitation are projected to increase which results in a steady decline of the glacier area. The river flow is projected to increase significantly due to the increased precipitation and ice melt and the transition towards a rain river. Rain runoff and base flow will increase at the expense of glacier runoff. However, as the melt water peak coincides with the monsoon peak, no shifts in the hydrograph are expected. [ABSTRACT FROM AUTHOR]

The most important climatological inputs required for the calibration and validation of hydrological models are temperature and precipitation that can be derived from observational records or alternatively from regional climate models (RCMs). In this paper, meteorological station observations and results of the PRECIS (Providing REgional Climate for Impact Studies) RCM driven by the outputs of reanalysis ERA 40 data and HadAM3P general circulation model (GCM) results are used as input in the hydrological model. The objective is to investigate the effect of precipitation and temperature simulated with the PRECIS RCM nested in these two data sets on discharge simulated with the HBV model for three river basins in the Hindukush-Karakorum-Himalaya (HKH) region. Six HBV model experiments are designed: HBV-Met, HBV-ERA and HBV-Had, HBV-MetCRU-corrected, HBV-ERABenchmark and HBV-HadBenchmark where HBV is driven by meteorological stations data, data from PRECIS nested in ERA-40 and HadAM3P, meteorological stations CRU corrected data, ERA-40 reanalysis and HadAM3P GCM data, respectively. Present day PRECIS simulations possess strong capacity to simulate spatial patterns of present day climate characteristics. However, also some quantitative biases exist in the HKH region, where PRECIS RCM simulations underestimate temperature and overestimate precipitation with respect to CRU observations. The calibration and validation results of the HBV model experiments show that the performance of HBV-Met is better than the HBV models driven by other data sources. However, using input data series from sources different from the data used in the model calibration shows that HBV-Had is more efficient than other models and HBV-Met has the least absolute relative error with respect to all other models. The uncertainties are higher in least efficient models (i.e. HBV-MetCRU-corrected and HBV-ERABenchmark) where the model parameters are also unrealistic. In terms of both robustness and uncertainty ranges the HBV models calibrated with PRECIS output performed better than other calibrated models except for HBV-Met which has shown a higher robustness. This suggests that in data sparse regions such as the HKH region data from regional climate models may be used as input in hydrological models for climate scenarios studies. [ABSTRACT FROM AUTHOR]

Abstract: Various remote sensing products are used to identify spatial–temporal trends in snow cover in river basins originating in the Himalayas and adjacent Tibetan–Qinghai plateau. It is shown that remote sensing allows detection of spatial–temporal patterns of snow cover across large areas in inaccessible terrain, providing useful information on a critical component of the hydrological cycle. Results show large variation in snow cover between years while an increasing trend from west to east is observed. Of all river basins the Indus basin is, for its water resources, most dependent on snow and ice melt and large parts are snow covered for prolonged periods of the year. A significant negative winter snow cover trend was identified for the upper Indus basin. For this basin a hydrological model is used and forced with remotely sensed derived precipitation and snow cover. The model is calibrated using daily discharges from 2000 to 2005 and stream flow in the upper Indus basin can be predicted with a high degree of accuracy. From the analysis it is concluded that there are indications that regional warming is affecting the hydrology of the upper Indus basin due to accelerated glacial melting during the simulation period. This warming may be associated with global changes in air temperature resulting from anthropogenic forcings. This conclusion is primarily based on the observation that the average annual precipitation over a five year period is less than the observed stream flow and supported by positive temperature trends in all seasons. [Copyright &y& Elsevier]

A field study was conducted to assess the location and the seasonal variation in physicochemical parameters of springs (outlets of underground water channels) of Bhetagad watershed of Uttaranchal hills, India. Traditionally, spring water is used for multiple purposes in this region. The average population density of the watershed is 366 persons km−2, distributed within an altitudinal range of 1,090–2,060 m a.m.s.l. and 23.52 km2 area. Twelve springs, in three different land uses e.g. pine forest, rainfed agriculture near settlements and irrigated agriculture near settlements were monitored in the winter (January), summer (June) and monsoon (August) during 1998 and 1999. The water quality parameters selected, in the present study are pH, EC, TDS, DO, free CO2, total hardness, Ca2+, Mg2+, CO3 2−, HCO3 −, Cl-, NO3 − and SO4 2− ions. Some springs in pine forests exhibit lower pH values than the permissible limit. Springs, with their location in agriculture and settlement, show slightly higher EC than the springs in pine forests. All the springs, near the irrigated agricultural land recorded higher nitrate ion concentration. [ABSTRACT FROM AUTHOR]

• Morphometric analysis integrated with sediment connectivity and stream power index. • Variable sediment flux in upper Ganga and upper Kosi basins linked to morphometric characteristics. • Variable hillslope-channel and catchment connectivity contributes to sediment flux variations. • Slope variations manifested in stream power index also influence sediment transport. • Morphometric characterization has significant implications for sediment management. The Indo-Gangetic basin exhibits highly diverse hydro-geomorphic settings that influence the hydrology, sediment production, and transport rates of the rivers draining this region, and this, in turn, is manifested in morphometric diversity of river systems. The rivers draining the western Gangetic plains (WGP) show incised channels attributable to high stream power and low sediment yield. In contrast, the rivers draining the Eastern Gangetic Plains (EGP) have formed aggradational landforms such as megafans due to low stream power and high sediment yield. For a better process understanding of the causal factors of such spatial inhomogeneities in a river basin, a morphometric characterization of its hinterland is necessary. In this work, a set of morphometric parameters such as stream network, longitudinal profile, and hypsometric curve have been integrated with data on sediment connectivity and stream power index to establish the form-process relationships in two contrasting basins, the upper Ganga basin (UGB) and the upper Kosi basin (UKB). The results of this study suggest that high sediment flux in the UKB is attributed to high rainfall, steep topography, unstable channel longitudinal profiles, and high sediment connectivity. A large part of these sediments gets deposited within the channel belt in the alluvial reaches and is remobilized during high flow events. However, the UGB produces fewer sediments due to low rainfall, mild topography, stable channel longitudinal profile, and low sediment connectivity. Also, the presence of a major dam at Tehri further reduces the functional sediment connectivity in the Upper Ganga Basin. [ABSTRACT FROM AUTHOR]

The water resources of Tamor River Basin in the eastern Himalayas of Nepal is heavily tapped for agricultural water use and hydropower production. Several studies show that the hydrology of the Himalayan River Basins is vulnerable to climate change. Topographical variations, data scarcity and its complex climate have always been barriers to achieving realistic simulation of the hydrological regime in the Himalayan River Basins, and the Tamor River Basin is no different. In hydrological response unit (HRU) based models, fixing the number of HRUs and sub-basins has a tendency towards confusion. This is especially true in regions with altitudinal and climatic variations. Therefore, this study aims to evaluate the SWAT model performance uncertainty associated with the number of sub-basins, HRUs, and elevation bands and quantify the impact of climate change on streamflows in the Tamor River Basin. Future climate scenarios were developed for three different time frames, the 2030s, 2060s, and 2080s, based on an ensemble of Coupled Model Intercomparison Project Phase 5 (CMIP5) and four Regional Climate Models (RCMs) under the Representative Concentration Pathways (RCP4.5 and RCP8.5) scenarios. The linear scaling method (LSM) of bias correction was used to bias-correct the climate data and then fed into the SWAT model to simulate the future streamflows of the basin. An increase in the annual average maximum temperature (+4 °C) and minimum temperature (+5.5 °C), and a decrease in precipitation (−4.5%) is projected by the end of the twenty-first century under RCP8.5 scenarios. The study found that the future climate could decrease the streamflow by over 8.5% during the twenty-first century under RCP8.5 scenarios. The results show elevation bands (EBs) to be more significant compared to HRUs and sub-basins (SBs) in getting a robust hydrological model in the Himalayan region. The estimates prepared in this study would be beneficial for hydropower developers, planners and policymakers, and water resource managers in developing adaptation strategies to offset the negative impact of climate change in the Tamor River Basin. Unlabelled Image • We calibrated SWAT model under different model setup scenarios in Himalayan basin. • Elevation bands found to be significant for hydrological modelling in the Himalayan region. • The model simulated future streamflow in future climate change scenarios. • Climate change is expected to decrease streamflow of Tamor river in future. [ABSTRACT FROM AUTHOR]

The incision of rivers into bedrock is considered as one of the most important processesdriving long-term landscape evolution. River incision is non-linearly dependent on riverdischarge, because river discharge must exceed a certain threshold to be able to transportbedload sediment and expose the riverbed to erosion. Fluvial erosion efficiency is, therefore,strongly controlled by the frequency and magnitude of flood events. In this study wehypothesise that catchment attributes, such as regolith thickness, lithology and vegetationcover, modulate the discharge response after a precipitation event, which has implications forthe fluvial erosion efficiency. We present preliminary results from a study, in which we exploit daily discharge recordsfrom 322 river gauging stations on a large climatic gradient in Chile (18˚ S-55˚ S). Thestudied rivers have catchment areas of 15 km2 to 24200 km2, which differ in topography,lithology, regolith thickness, vegetation cover and snow and glacier cover. First, we studieddischarge variability (i.e. magnitude-frequency distribution of flood events) andthe occurrence of different discharge regimes as result of seasonal variations, byobtaining the best fit of a weighted sum of two inverse gamma functions to the data(Scherler et al., 2017). Each of the distributions is interpreted to correspond to oneflow regime. When the weighted sum of two inverse gamma functions performedbetter than one, and each flow regime lasted at least 3 months, we interpret thedifferent flow regimes to reflect seasonal variation in a catchment. Results reveal largevariations in discharge variability along the climate gradient and strong seasonalvariations around 30˚ S-40˚ S which is mainly driven by climatic forcing and snowmelt. We are currently studying discharge variability by obtaining the flood flashinessparameter, the variability index and hydrologic response time from fitting the streamflowrecession model to the daily discharge records (Deal et al., 2018 after Botter et al., 2007). Wewill focus on the differences between seasons and El Niño, La Niña and normalyears and will compare all parameters with calculated topography and datasets ofclimate, vegetation density, regolith thickness, lithology and snow and glacier cover todisentangle their controls on flood flashiness, variability index and hydrologic responsetime. References: Botter, G., Porporato, A., Rodriguez-Iturbe, I. and Rinaldo, A.: Basin-scale soil moisturedynamics and the probabilistic characterization of carrier hydrologic flows: Slow,leaching-prone components of the hydrologic response, Water Resour. Res., 43(2),1–14. Deal, E., Botter, G. and Braun, J.: Understanding the role of rainfall and hydrology indetermining fluvial erosion efficiency, J. Geophys. Res. Earth Surf., 2018. Scherler, D., DiBiase, R. A., Fisher, G. B. and Avouac, J. P.: Testing monsoonal controlson bedrock river incision in the Himalaya and Eastern Tibet with a stochastic-thresholdstream power model, J. Geophys. Res. Earth Surf., 122(7), 1389–1429, 2017. [ABSTRACT FROM AUTHOR]