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• Indian Northwestern Himalayan lakes are sole sources of water at many locations. • Anthropogenic alterations have an adverse impact on lake water quantity and quality. • Tourism and land use land cover changes have led to degrading lake systems. • Void in knowledge of hydroecology of lake systems inhibits sustainable management. • Need for holistic lake studies with long term hydroecological monitoring. The Himalayas are dotted with a multitude of freshwater lakes of varying sizes. These lakes serve as the sole source of water for multiple major human settlements in the region and a backbone to socio-economic services. Here, we provide a comprehensive review of the available literature on hydro-ecology of important lakes in the Indian Northwestern Himalayas (INWH). Numerous studies have been performed in the past but are reported in regional journals, scientific reports of government research institutions and local conference proceedings with a very few publications in the international journals. We attempt to synthesize the available scientific knowledge in view of topography, climate, hydrology, water quality, land use land cover (LULC), sedimentation, climate change, and other anthropogenic influences. Our review reveals that INWH lakes are adversely affected by multiple anthropogenic influences including, population growth, LULC modifications and deforestation, urbanisation, intensified agricultural, wastewater disposal, excessive freshwater abstraction, and tourism. It is leading to a widespread decline in water quality and adverse impacts on the ecological status of lakes across the INWH region. Signals of climate change impacts are also reported in the region, evident as a significant reduction in precipitation and warming of temperature in historical records, along with projections of an increasing rate of change in future climate. Sustainable management of INWH lakes to preserve their unique hydroecological attributes will require integrative limnological studies that include climate, hydrology, water quality, and ecology. It will provide a body of evidence for developing conservation practices and policies to protect the INWH lakes, prioritise restoration activities, and sustain their role as socio-economic assets. The studies need to prioritise long-term field-based limnology research and high-frequency, high-density monitoring stations while developing practices and policies to alleviate the immediate threats from LULC, water abstraction, and human perturbances. [ABSTRACT FROM AUTHOR]

• Kolahoi Glacier had higher mass loss more than the majority of Western Himalayan glaciers. • Mass balance of the glacier during 1980–2019 shows significant inter-annual variation. • Glacier mass loss showed a good relation with observed temperature and precipitation. • Glacier mass loss and depleting glacier-melt streamflow exhibits a strong link. Knowledge of glacier mass balance (MB) is critical for understanding glacier-climate interactions and projecting future water availability in the data-scarce Himalayan region. In this study, we present the glaciological (2014–2019), geodetic (2000–2014) and reconstructed (1980–2019) MB of the Kolahoi Glacier (KG) in the Kashmir Himalaya, India. During the five-year observation period, the average in situ MB of the Glacier was −0.83 ± 0.34 m w.e. a−1, with significant inter-annual variation. The mean annual geodetic MB of the KG between 2000 and 2014 was −0.90 ± 0.09 m w.e. The reconstructed MB revealed four distinct glacier recession episodes since 1980. The Period I (1980–1990) showed a reduced mass loss of −0.27 ± 0.42 m w.e. a−1, with four years of positive mass balance. The Period II (2000–2010), on the other hand, experienced the highest mass loss of −1.18 m w.e. a−1 throughout the entire reconstructed MB series. All three MB measurement- in situ, geodetic and simulated agreed well. The MB showed an excellent correspondence with the observed temperature and precipitation. Analysis of the data revealed that the MB is sensitive to temperature at the rate of −0.65 m w.e. a−1 °C−1, but the sensitivity is only 0.13 m w.e. a−1 for a 10% change in precipitation. Furthermore, there is a good correlation between the simulated glacier mass loss and depleting glacier-melt in the autumn streamflow. The mass loss of the KG is expected to exacerbate in future as a result of the projected climate change, and thus further diminishing the streamflow of the transboundary rivers emanating from the region. It is envisaged that the findings will contribute to a better understanding of glacier-climate interactions and their implications for future water availability in the Kashmir Himalaya. [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: This paper reports a study of the Tista megafan in the foothills of Darjeeling Himalaya. Spread over parts of India and Bangladesh, the megafan is bounded by the Mahananda River to its west and the Tista River to the east. The Atrai and Karatoya Rivers flow through its axial part. The megafan covers an area of ~18,000km2. Near its apex the surface slope is ~0.19°, that declines to 0.01° near the toe. The east–west transverse profile of the megafan is broadly upward convex, with gently sloping (~0.01°) flanks. Maximum width and the length of the megafan are about 145km and 166km respectively. The highest point near the megafan apex is ~150m above the Brahmaputra alluvial plain. The Tista River flanking the megafan has an average annual discharge of 609m3/s with highest average monthly discharge exceeding 2000m3/s during monsoon. Most of the other channels currently traversing the megafan are plains-fed, and compared to Tista and Mahananda Rivers these channels have lesser discharge, higher sinuosity, and decreased widths. A radiating network of abandoned channel belts can be identified in satellite images of the megafan. Each of these major paleochannels is associated with numerous crevasse channels in the distal part of the megafan, forming an intricate network of radial drainage on the megafan surface. Three distinct depositional lobes can be recognised on the Tista megafan. Each of the lobes is identified by a set of ancient and modern radial drainage systems. The lobe boundaries are marked by discordance in drainage network of adjacent lobes. The relative ages of the lobes, as tentatively determined from the drainage discordances, indicate that the megafan first built up the eastern lobe (lobe 1), then shifted to the west to form lobe 2, and finally switched again eastward giving rise to the smallest lobe located close to the mountain front (lobe 3). Although broadly upward convex in cross profiles, subtle reflections of multiple lobes are apparent in some of the cross profiles. Study of the old maps published between 1794 and 1945 reveals that some of the present-day plains-fed rivers, like the Tangon, the Atrai and the Karatoya, were directly connected to the Himalayan catchment basins prior to the late eighteenth century. Archaeological excavations along the banks of these rivers appear to support this paleodrainage configuration. Eight facies and five facies associations were recognised in the uppermost megafan sediments. Facies associations suggest deposition from high-energy sandy streams in the proximal area and deposition from mixed load, sinuous streams and flanking marsh or lake in the distal part of the lobes. Paleocurrent data are consistent with a southwestward spreading paleochannel pattern recognised within the studied part of the megafan. Multiple lobes typify megafans ocurring in different parts of the globe. The existence of the mutiple accretionary lobes in Tista megafan, its radial drainage pattern, its concave-upward longitudinal and convex-upward transverse profile shape make it morphologically comparable with other high-gradient alluvial fans observed in nature and those produced in the laboratory. These morphological features denote the similarities between the small, high-gradient alluvial fans and large, low-gradient megafans, and that in turn may be indicative of the commoness in certain controlling factors between these two depositional systems. [Copyright &y& Elsevier]