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Spring constitutes one of the primary water resources in some parts of the world, such as the Indian Himalayas. However, these remain imperfectly surveyed and delineated far and wide in most areas worldwide. Due to natural and anthropogenic factors, the springs are under great threat. All over the globe, springs have left as data deficit and have not relatively gained considerable attention in comparison to other systems like rivers, streams, lakes, and wetlands. This is also true for India, where most of the research is usually centered on groundwater, rivers, lakes and wetlands. This manuscript presents an overview of studies carried out on various themes of spring water systems, such as characteristics, classification schemes, and different empirical and analytical methods at international and national levels. A comprehensive overview of the literature identified the demand for an integrated approach of different empirical and analytical methods to strengthen the understanding of spring hydrology in the Himalayan region and elsewhere. Research highlights: Springwater system protection needs a forewarning of imminent contamination and thus, an integrated approach of conceptual and management-related groundwater models should be developed in India on a large scale. Empirical and analytical approaches should be used to attain an inclusive understanding of springwater hydrology and water quality. Himalayan springs should be studied considering the current updated classification schemes to obtain a comprehensive understanding of them. Monitoring of data and simulation models should be developed to establish an integrated and comprehensive understanding of Himalayan spring hydrogeology and hydrology. [ABSTRACT FROM AUTHOR]

In the Himalayas, the lives and livelihoods of millions of people are sustained by water resources primarily depending on the moisture brought by Western Disturbances and Indian Summer Monsoon. In the present study, a network of 12 precipitation stations was established across the Kashmir Valley to understand the spatial and meteorological factors controlling precipitation isotopes. Temperature and relative humidity are dominant meteorological factors, whereas altitude, proximity to forest canopy, land use/land cover, windward and leeward sides of the mountains are the main physical factors influencing precipitation isotopes. The study suggests that the Mediterranean Sea and nearby water bodies along with continental recycling are the dominant sources of moisture from October to May, while the Arabian Sea, Bay of Bengal and continental recycling are the main sources of moisture from June to September. However, some precipitation events from October to May collect moisture from the Arabian Sea and some precipitation events from June to September collect moisture from the Mediterranean Sea. The occasional passage of Western Disturbances in summer merging with the Indian Summer Monsoon yields heavy to very heavy precipitation. The study provides a better understanding of complex spatial and meteorological phenomena controlling precipitation isotopes across the Western Himalayas. [ABSTRACT FROM AUTHOR]

• 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]

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]

• 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]

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]