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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]

The interactive role of life-history traits and environmental factors on plant water relations is crucial for understanding the responses of species to climate change, but it remains poorly understood in secondary tropical montane forests (TMFs). In this study, we examined differences in sap flow between the pioneer species Symplocos racemosa and Eurya acuminata , and the late-successional species Castanopsis hystrix that co-occur in a biodiverse Eastern Himalayan secondary broadleaved TMF. The fast-growing pioneers had sap flux densities that were 1.6–2.1 times higher than the late-successional species, and exhibited characteristics of long-lived pioneer species. Significant radial and azimuthal variability in sap flow (V) between species was observed and could be attributed to the life-history trait and the access of the canopy to sunlight. Nocturnal V was 13.8% of the daily total and was attributable to stem recharge during the evening period (18.00–23.00 h) and to endogenous stomatal controls during the pre-dawn period (00.00–05.00 h). The shallow-rooted pioneer species both exhibited midday depression in V that was attributable to photosensitivity and diel moisture stress responses. In contrast, the deep-rooted late-successional species showed unaffected transpiration across the dry season, indicating their access to groundwater. Thus, our results suggest that secondary broadleaved TMFs, with a dominance of shallow-rooted pioneers, are more prone to the negative impacts of drier and warmer winters than primary forests, which are dominated by deep-rooted species. Our study provides an empirical understanding of how life-history traits coupled with microclimate can modulate plant water use in the widely distributed secondary TMFs in Eastern Himalaya, and highlights their vulnerability to warmer winters and reduced winter precipitation due to climate change. [ABSTRACT FROM AUTHOR]

Many global climate models, including the Climate Forecast System version 2 (CFSv2), have a biased representation of subseasonal modes of variability of the Indian summer monsoon. For instance, they simulate a weaker summer mean monsoon low‐pressure systems (LPS) climatology, faster than observed northward propagation of monsoon intraseasonal oscillations (MISOs), and a systematic dry bias over Indian landmass. The Bay of Bengal (BoB), with its shallow mixed layers and unique thermal stratification, significantly modulates the convective activity in this region at subseasonal‐to‐seasonal timescales through modulation of sea surface temperature. The highly stratified upper ocean in the BoB is due to the enormous freshwater it receives from rains and rivers. A river routing model is coupled to the CFSv2 to account for the riverine freshwater and the improvements in modelling the upper‐ocean structure are analysed. Model simulations indicate that inclusion of temporally varying riverine freshwater improves the upper‐ocean state in the BoB and the observed mixed‐layer temperature gradients in the Bay are simulated reasonably after incorporating the time varying river runoff. This resulted in increased LPS lifetime and track density, and enhanced rainfall over central India. Better representation of the upper‐ocean stratification in the model leads to larger post‐convection shoaling of mixed layers at intraseasonal timescales, thereby forming thick barrier layers. Enhanced air–sea interactions restricted to the shallow mixed layer are associated with stronger vorticity, specific humidity and low‐level convergence to the north of the intraseasonal convection band. This enhanced low‐level moisture convergence north of the convection centre results in realistic northward propagation of MISO and aids LPS activity. It is demonstrated that better simulation of the upper‐ocean structure in coupled climate models can improve the representation of subseasonal modes of monsoon variability. These results bear important implications for operational forecasting. [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]

An accurate streamflow forecast is vital for flood prediction and early warning systems. Notwithstanding the rising frequency and intensity of floods during the summer monsoon season in India, efforts to examine the utility of data assimilation (DA) for streamflow prediction remain limited. We examine soil moisture and streamflow DA to improve streamflow simulations in the Narmada River basin, considered a testbed. Data assimilation was performed using the Variable Infiltration Capacity (VIC) model at four gauge stations in the basin. First, we used the ensemble Kalman filter (EnKF) to assimilate the satellite soil moisture from the European Space Agency Climate Change Initiative (ESA-CCI) to the initial state of the VIC model. We examined the usefulness of observed streamflow from the India Water Resources Information System (India-WRIS) to improve the initial hydrological conditions of the VIC model in the streamflow DA during the summer monsoon (June–September) season from 1980 to 2018. The assimilation of ESA-CCI soil moisture showed less improvement in percent error reduction (PER) and efficiency index (EFF) (less than 2%) than the streamflow DA at all of the four gauge locations in the Narmada basin. On the other hand, the streamflow DA showed a significant improvement in PER and EFF (more than 10%) at all the gauge stations for both mean and high-flow conditions. Streamflow data assimilation improved errors in the magnitude and timing for the major floods in 1994 and 2013. Significance Statement: India is considerably affected by floods during the summer monsoon. Floods have increased and are projected to become more frequent under the warming climate. Flood prediction and early warning systems are essential in reducing their impacts and exposure. In the present study, we are interested in examining the role of soil moisture and streamflow data assimilation on flood prediction in the Narmada River basin. Our results show that streamflow data assimilation is more effective in reducing errors and bias in streamflow prediction than soil moisture data assimilation. The hydrologic framework used for the Narmada basin can be extended and evaluated to other flood-prone basins in India. [ABSTRACT FROM AUTHOR]

Water harvesting is a critical component of any approach to alleviating India's water crisis. Traditional rainwater harvesting systems are found in every region of the country. Haveli is one such system found in almost every village in the Bundelkhand region, Uttar Pradesh, India. A defunct Haveli in the Parasai-Sindh watershed of Jhansi district, Uttar Pradesh, was rejuvenated by providing a cement concrete core wall to the earthen embankment to address the problem of breaching, and the existing outlet was also expanded. This study was conducted from 2013 to 2019 to analyse the hydrology of the rejuvenated Haveli and to understand its impact on surface-water availability and recharging groundwater. The study period was divided based on long-term southwest monsoon (SWM) as wet (SWM > 20%), normal (SWM ± 20%) and dry (SWM < 20%) years. It was found that the Haveli could harvest about 1.91-2.0 times, 1.13-1.72 times and 0.2 times its capacity during a wet, normal and dry year, respectively. There was a 1.41 m difference in hydraulic head between pre- and post-Haveli rejuvenation in a wet year, whereas, a normal year, the difference was 2.71 m. [ABSTRACT FROM AUTHOR]

Stable water isotopes in ground-level vapour are key to estimating water exchange between geospheres. Their sampling, however, is limited to laser-absorption spectrometers and satellite observations, having inherent shortcomings. This study investigates diffusive kinetic fractionation during liquid condensation under supersaturated environment, providing a cost-effective, reliable way of sampling ground-level vapour isotopes (18O, 2H). Experiments were undertaken at three locations in India with 'liquid' samples collected from condensation of ambient air at 0°C. Simultaneously, pristine 'vapour' was sampled via cryogenic-trapping using liquid nitrogen–alcohol slush at –78°C. The 'liquid' condensed under supersaturation was progressively more depleted in 18O, and less enriched in 2H than expected under equilibrium fractionation, with an increasing degree of supersaturation expressed as saturation index (Si). This study revealed: (1) Si, molecular density, Rh, T together control the extent of isotopic kinetic fractionation. (2) The presence of diffusive concentration gradient inhibits the flow of heavier isotopes during liquid condensation. (3) The stochastic nature of the process cannot be explained using a physics-based model alone. The artificial neural network model is hence deployed to sample δ18O (δ2H) within –0.24 ± 1.79‰ (0.53 ± 11.23 ‰) of true value. (4) The approach can be extended to ground-validate isotope-enabled general circulation models and satellite observations. [ABSTRACT FROM AUTHOR]

An important goal of the Surface Water and Ocean Topography (SWOT) mission is to provide river width, height, slope to estimate global river discharges. To appraise the feasibility of SWOT data over India, the present study utilizes the SWOT simulator from Centre National D'Etudes Spatiales (CNES) to generate a long time-series (three years) of SWOT observations over the Mahanadi River basin in India. Two independent sources of river geometry are used in this study, namely satellite-based and hydrodynamic model-based estimates. Satellite-based river geometry is derived using a web-based User Interface (UI) developed in-house to generate time series of accurate river width shapefiles from Sentinel-1 satellite imagery. To compare these results, a 1D unsteady flow analysis is carried out over the Mahanadi River to simulate channel water depth and inundation extent using the Hydrologic Engineering Center's River Analysis System (HEC-RAS) model. The simulated observations are used in this study to assess the potential error in SWOT channel water depth measurements. Results indicate a good spatial correlation between the water surface area derived from Sentinel and HEC-RAS models with a correlation of 0.74. The simulated data shows a bias of 20 cm compared to gauge observations. This study is conducted as a proof of concept in demonstrating the ability of simulated SWOT data in capturing river water surface elevation with respect to the conventional HEC-RAS model. It also implements a new tool in google earth engine (GEE) to generate input to SWOT simulator. [ABSTRACT FROM AUTHOR]

• Assessing rural water use patterns and water-covered areas in Nagaon, India. • Employing participatory methods for community insights. • Degradation of surface water bodies from increased reliance on groundwater. • Decline in flora and fauna linked to changing water use and water-covered areas. • Community engagement in policy-making for ecohydrological conservation & restoration. The use and management of water resources are fundamental for sustainable human societies, economic development, and ecological conservation. Therefore, conducting a thorough investigation to comprehend water use (WU) patterns and assess the extent of water-covered areas (WCA) in a region is indispensable for fostering sustainable ecological and economic conditions, and for implementing effective water management practices. However, the rapid growth of human populations, particularly in developing countries, and the concomitant developmental activities have significantly influenced the WCA, leading to their degradation and loss. In this context, the present research focuses on investigating and understanding the variations in WU and WCA, with an emphasis on unraveling the ecological implications of these hydrological dynamics in the rural areas of Nagaon-a floodplain district of the middle Brahmaputra valley in Assam, India. The study also seeks to investigate the intricate and dynamic human-water relationship and their impact on the waterscapes and the associated hydroecological characteristics. The methodology employed in this study involved analyzing spatial data and conducting field surveys to procure some other relevant primary data and information to assess the current state of WU and WCA in the district. The results reveal substantial shifts in water usage patterns, with a growing reliance on groundwater and reduced dependence on surface water bodies. Notably, all wetlands, except the artificial ponds (pukhuris), have experienced significant declines in both quantity and size, resulting in a reduction of WCA and the associated aquatic vegetation cover. This reduction in WCA has consequently led to a substantial decline in wetland habitats and disruptions to their ecological conditions, posing serious threats to the floral and faunal species dependent on these aquatic ecosystems. The findings of this research will definitely help the concerned policymakers, environmental organizations, and local communities by providing a foundation for informed decision-making towards formulating effective conservation strategies to safeguard not only the WCA of the district but also to maintain the region's ecological health, proper water use, and the sustainable socio-economic development. [ABSTRACT FROM AUTHOR]

The SCATSAT-1 (Scatterometer Satellite) was launched by ISRO (Indian Space Research Organisation) on September 26, 2016 from the Satish Dhawan Space Centre, Sriharikota, India. With nearly five years of its journey, the Ku-band (13.5 GHz) based SCATSAT-1 made a profound impact on many scientific domains such as ocean-atmosphere dynamics, soil moisture and vegetation dynamics, climate change, hydrology and polar sea-ice and snowmelt studies. As a successor of the Oceansat-2 Scatterometer (OSCAT), the SCATSAT-1 supports the long-term analysis in climate studies, crop yield prediction, and forecasting analysis. In addition, the SCATSAT-1 provides the four different levels of data products at an enhanced resolution to improve the scope of the scatterometer in different applications. Recently the SCATSAT-1 has been explored in many emerging applications apart from oceanography e.g., crop growth, snow cover analysis, jute crop detection and river level estimation with advanced algorithms i.e., machine learning-based classification, information fusion, and super-resolution mapping. Therefore, it is desired to summarise all operational SCATSAT-1 products, applications, and their emerging trends at the global level in the various scientific domains. This paper has summarized the progress made by SCATSAT-1 in different scientific domains since its launch. A meta-analysis has also been conducted in this paper (using the SCOPUS database) to analyse the current research status of SCATSAT-1 in terms of study area targets. This study highlights the features, challenges, and future directions for the scatterometer improvements. • To summarise the historic & current scatterometer missions for earth exploration. • To know the physics & chemistry of earth using data products of SCATSAT-1. • To explore the applications in cryosphere, oceanography, agriculture & hydrology. • To analyse the current status through meta-analysis of published articles. • To summarise the challenges & future directions for the scatterometer improvements. [ABSTRACT FROM AUTHOR]

• Anthropogenic water regulation (AWR) has incorporated into the CIESM model. • The worldwide TWS simulation results improve with AWR incorporation. • The impact of AWR on regional hydroclimate change is significant. This study examines the impact of anthropogenic water regulation (AWR) on hydroclimatic systems by incorporating an AWR module into the Community Integrated Earth System Model (CIESM), validated against GRACE satellite data. This approach assesses the influence of human activities, including irrigation and groundwater extraction, on global and regional hydrology and climate. Key findings include: Implementation of the AWR module significantly improves terrestrial water storage (TWS) simulation accuracy in CIESM. The correlation coefficient for global-scale TWS improved from 0.33 in the control (CTRL) to 0.89 in the experiment (EXP). Notably, the model's performance enhanced in Northern India and the North China Plain, while the Central United States showed limited improvement. AWR markedly alters the global water cycle, evidenced by substantial increases in soil moisture (about 0.04 to 0.02 m3/m3) and evapotranspiration. These changes have led to increased latent heat flux (around 5 W/m2) and a decrease in temperature by 0.1 °C to 1 °C in heavily irrigated regions. The study highlights the role of AWR in modifying the energy balance, particularly in agricultural areas where irrigation exerts a significant cooling effect. Despite its potential, the study identifies considerable uncertainties in coupling AWR within the CIESM model, related to inherent model limitations, incomplete water intake data, variable groundwater levels, and simplifications in water transfer parameters. Future research should aim to refine these aspects, focusing on enhancing the physical mechanisms and performance of AWR modules in hydroclimatic simulations. In conclusion, this research underscores the substantial modifications in hydrological and climatic conditions due to human activities. The improved AWR scheme within CIESM provides valuable insights for understanding and predicting climate change impacts on water resources, demonstrating its utility in simulating complex hydroclimatic changes at both global and regional scales. [ABSTRACT FROM AUTHOR]

The efforts to develop a hydrologic model-based operational streamflow forecast in India are limited. We evaluate the role of bias correction of meteorological forecasts and streamflow postprocessing on hydrological prediction skill in India. We use the Variable Infiltration Capacity (VIC) model to simulate runoff and root-zone soil moisture in the Narmada basin (drainage area: 97 410 km²), which was used as a testbed to examine the forecast skill along with the observed streamflow. We evaluated meteorological and hydrological forecasts during the monsoon (June--September) season for the 2000--18 period. The raw meteorological forecast displayed relatively low skill against the observed precipitation at 1--3-day lead time during the monsoon season. Similarly, the forecast skill was low with mean normalized root-meansquare error (NRMSE) more than 0.9 and mean absolute bias larger than 60% for extreme precipitation at the 1--3-day lead time. We used empirical quantile mapping (EQM) to bias-correct precipitation forecasts. The bias correction of precipitation forecasts resulted in significant improvement in the precipitation forecast skill. Runoff and root-zone soil moisture forecasts were also significantly improved due to bias correction of precipitation forecasts where the forecast evaluation is performed against the reference model run. However, bias correction of precipitation forecasts did not cause considerable improvement in the streamflow prediction. Bias correction of streamflow forecasts performs better than the streamflow forecasts simulated using the bias-corrected meteorological forecast. The combination of the bias correction of precipitation forecasts and postprocessing of streamflow resulted in a significant improvement in the streamflow prediction (reduction in bias from 40%to 5%). [ABSTRACT FROM AUTHOR]

• Pulse reserve paradigm observed across biomes over India. • Pulse reserve is distinctly visible from both X and L-band satellite data. • Spatio-temporally and seasonally varying Pulse reserve characteristics. • Pulse reserve characteristics sensitive to pulse soil moisture and EVI. • These characteristics less sensitive to clay fraction opposed to global traits. The pulse-reserve paradigm associated with the plant's increased water uptake following surface soil moisture pulses is not well understood in India. India has a very high spatio-temporal climate and ecological variability. Such ecological and climatological diversity makes the country-scale analysis of the pulse-reserve paradigm challenging. Here, we present the first analysis of this phenomenon using 9 years of space based passive microwave estimates of surface soil moisture and vegetation water content from both X-band and L-band. We observed from both datasets that the pulse-reserve paradigm is widespread in India across seasons and biomes. The seasonal climate in India drives the precipitation characteristics, thus uphold the pulse-reserve paradigm. The estimated Soil Moisture Threshold (SMT), at which the vegetation water content drops, has substantial spatio-temporal variations, unlike other regions worldwide. The comparisons between X-band and L-band products show significant differences in the magnitudes of soil moisture and vegetation optical depths due to inherent properties. However, most of the findings related to the pulse-reserve paradigm, specifically the sensitivity of processes on different factors, remain similar. We found a strong dependence of SMT on seasonal climate, vegetation greenness, and pulse soil moisture. The association of SMT with soil characteristics, such as clay fraction, is weak in India, contrary to global traits. Our analysis provides new insights into the plant water uptake mechanisms in India to improve the parameterization schemes for better representation of the soil–plant continuum structural and functional behavior. [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]

The present study aims to illustrate the efficacy of socio-hydrology in understanding the interaction between coupled human and water systems for sustainable water resource management. Future Land use land cover (LULC) growth is projected under four scenarios – business as usual (BAU), sustainable growth (SG), exponential growth (EG-1 and EG-2), and combined sustainable and economic growth (CS-EG) – for the Subarnarekha basin of India. The associated impacts of the scenarios on hydrological processes are simulated using an integrated modelling system that combines a physically based distributed hydrological model (MIKE SHE/MIKE HYDRO RIVER) and a spatially explicit integrated LULC change model (multilayer perceptron Markov model). The magnitudes of different hydrological variables suggest SG as the most favourable scenario. In contrast, the CS-EG scenario is the most plausible scenario based on the signal-to-noise ratio. The findings may provide valuable knowledge for future LULC planning in the basin. The study suggests incorporating a citizen science approach in LULC planning to reflect local preferences in the decision making process. [ABSTRACT FROM AUTHOR]

Wetlands play an important ecological role by providing shelter and habitat for diverse fish species, migratory birds, macrophytes and other aquatic organisms. Hydrological connectivity with the main river channel has a critical role in fish diversity and production in floodplain wetland. The present study showed the seasonal hydrological alteration on fish species distribution in Ansupa wetland, connected with tropical river Mahanadi, India. The river discharge showed a variation from 4549 cusec during lean season (April) to 204716 cusec during monsoon (August). It has been recorded that water flows/discharge above 200000 cusec only, inundate the wetland resulting in exchange of free flows of fish species and nutrients. The study period for the fish species diversity was undertaken during 2017-18. A total of 46 fish species were observed under the orders Cypriniformes (18), Perciformes (12), Siluriformes (7), Synbranchiformes (2), Cyprinodontiformes (1), Clupeiformes (1), Beloniformes (1), Osteoglossiformes (1), Mugiliformes (1), Anguilliformes (1) and Tetraodontiformes (1). According to the conservation status of the International Union for Conservation of Nature, four species Parambassis lala, Ompok bimaculatus, and Anguilla bengalensis are in the category of Near Threatened. Analysis showed that taxonomic distinctness is more during winter than the monsoon and pre-monsoon, indicating monsoon could play a significant role in the fish species recruitment through river connectivity. Climatic data was analysed for a period of 34 years and indicated that an increment of 0.20C in water temperature and average increase of 129mm rainfall at the study site. This slight increase in rainfall over the years could be one of the factors responsible for the fish recruitment in the Ansupa wetland, through river connectivity underlining the importance of flood for wetland fisheries recruitment and sustainability. [ABSTRACT FROM AUTHOR]

Every year, during the monsoon period (June–September), series of land subsidence incidences are reported from the Southern Western Ghats in India. These land subsidences occur primarily due to subsurface erosion, which leads to formation of soil pipes. These soil pipes are geo-morphologically an outcome of land degradation process that significantly influences the hill slope hydrology which makes the slopes vulnerable, and affects the human lives as well. However, detection of these subsurface pipes remains a serious challenge. Most of the previous studies are based on surface investigations, without considering the subsurface features. The present study aims to provide a more detailed account of these less-studied geomorphic features (soil pipes) using an integrated approach. The main purposes of the present study are to 1) describe the characteristic of the soil pipes and 2) to quantify the scale of piping activity; based on both surface and subsurface investigations in watershed scale. The remote sensing and GIS platform were used to delineate watershed boundary, identify geo morphological setup of the terrain, detailed landuse information and to bring out change in landuse, landcover pattern. The geomorphic mapping was carried out to identify the type of pipes, location of its inlet, outlet and other subsequent deformation features. The resistivity survey was done to map geometry of the pipe, piping network, subsurface lithology, and get the water table depth. The resistivity survey results indicate that the density of pipes are more than the estimated through surface mapping. Similarly, the length of the pipes is more than the mapped pipe through the surface mapping. The combined results suggest that the region is rich in these kinds of pipe features and may create hazard to the society residing in those areas. This study further underlined the importance of detailed study about soil piping phenomena to minimize its threat to human habitation and to provide specific recommendations to prevent the recurrence. [ABSTRACT FROM AUTHOR]

Accurate estimation of ET0, and determination of its trend/variability and sensitivity to changes in climate variables is essential at regional scale for different applications. These are attempted for India by considering 18 homogeneous ET0 regions formed in companion paper. Food and Agriculture Organization (FAO) recommends Penman–Monteith (PM) equation for ET0 estimation, which requires information on several climate variables. The equation cannot be used in data‐sparse areas where information/forecasts on one or more required climate variables is unavailable/unreliable. To address this, relevance vector regression (RVR) relationships are developed in this paper for the 18 homogeneous regions to arrive at FAO‐PM estimate of ET0 from subsets of its predictor climate variables, which could be typically expected in data‐sparse areas. The developed relationships are shown to be better in arriving at ET0 estimates when compared to multiple linear regression (MLR) relationships and three widely used empirical equations (Hargreaves, Mcguinness–Bordne, Priestly–Taylor). Regional trend analysis revealed that ET0 is significantly decreasing (increasing) in most regions located in north (south) India. Sensitivity of ET0 and surface runoff to changes in their predictor climate variables is determined for each region by considering third‐order Taylor series approximation of their functional relationships. Key climate variable(s) that govern ET0 changes in each region are identified. Results indicate that at annual scale solar radiation and relative humidity govern ET0 changes in regions located in south and north‐east India, whereas wind speed followed by relative humidity mostly influence the ET0 changes over other regions. Existence of evaporation paradox in four regions and validity of Bouchet's complementary relationship between ET0, actual evapotranspiration (ETa), and precipitation in 11 regions is also established. Significant divergence in trend of ET0 and ETa was evident in north‐east India. [ABSTRACT FROM AUTHOR]

Groundwater is rapidly depleting in India primarily because of pumping for irrigation. However, the crucial role of crop growth at annual and seasonal time scales in groundwater storage variability remains mostly unexplored. Using the data from the Gravity Recovery Climate Experiment (GRACE) satellites and well observations, we show that crop growth is negatively correlated with groundwater storage at annual and seasonal time scales in north India. Precipitation is positively associated with groundwater storage variability at the yearly time scale in north-central India (NCI) and south India (SI). In contrast, precipitation is negatively correlated with groundwater storage from the GRACE satellites in northwest India (NWI). The negative correlation between precipitation and groundwater from the GRACE in NWI is primarily due to groundwater depletion due to anthropogenic pumping from deep aquifers. Precipitation and groundwater storage from the well observations are positively correlated in all the three regions, indicating the influence of precipitation on shallow aquifers. Analysis of the two main crop growing seasons (Rabi and Kharif) showed that crop growth is negatively related to groundwater storage in both Kharif (June–September) and Rabi seasons in north India (NWI and NCI). Groundwater contributes more than precipitation in NCI during the Kharif season and in NWI and SI during the Rabi season. Granger's causality test showed that groundwater is a significant contributor to crop growth in NWI and NCI in both Kharif and Rabi seasons. Our results highlight the need for agricultural water management in both the crop growing seasons in north India for reducing the rapid groundwater depletion. [ABSTRACT FROM AUTHOR]

The low-frequency evolution of Indian rainfall mean-state and associated interannual-to-decadal variability is discussed for the last 6000 years from a multi-configuration ensemble of fully coupled global transient simulations. This period is marked by a shift of Indian Summer Monsoon Rainfall (ISMR) distribution towards drier conditions, including extremes, and a contraction of the rainy season. The drying is larger in simulations with higher horizontal resolution of the atmosphere and revised land surface hydrology. Vegetation–climate interactions and the way runoff is routed to ocean modulate the timing of the monsoon onset but have negligible effects on the evolution of seasonal rainfall amounts in our modeling framework in which carbon cycling is always active. This drying trend is accompanied by changes in ISMR interannual-to-decadal variability decreasing over north and south India but increasing over central India (20°–25° N). The ISMR interannual-to-decadal variability is decomposed into six physically consistent regimes using a clustering technique to further characterize its changes and associated teleconnections. From 6 to 3.8 kyr bp, the century-to-century modulations in the frequency of occurrence associated to the regimes are asynchronous between the simulations. Orbitally-driven trends can only be detected for two regimes over the whole 6–0 kyr bp period. These two regimes reflect increased influence of ENSO on both ISMR and Indian Ocean Dipole as the inter-hemispheric energy gradient weakens. Severe long-term droughts are also shown to be a combination of long-term drying and internally generated low-frequency modulations of the interannual-to-decadal variability. [ABSTRACT FROM AUTHOR]

Sediment transport is one of the major challenging fields in hydrology. The tropical atmosphere, complex topography and occasional extreme precipitation are the fundamental explanations behind this challenge. Thus, the rivers in this situation contain a huge quantity of sediment, which may affect the river hydraulics. Hence, it is required to collect various parameters such as discharge, velocity, rainfall and sediment concentration to analyze the impact of sediment for river engineering practices and management. Therefore, the dataset which is collected from the river may contain outliers and noises. For improving the prediction accuracy of sediment load, we present robust regularized extreme learning machine frameworks to reduce the effect of noise by using the asymmetric Huber loss function named as AHELM and ε - insensitive Huber loss function named as ε - AHELM. Further, the problems are rewritten in the form of strongly convex minimization problems whose solutions are acquired by simple function iterative schemes. To ensure the effectiveness of the proposed approach, we have considered the real-world datasets with two types of noises. Furthermore, the proposed schemes are applied on real sediment load datasets (SLDs) which are collected from the Tawang Chu river of Arunachal Pradesh, India. The results reveal that proposed AHELM and ε - AHELM with multiquadric activation function are performed better for real-world datasets, whereas AHELM and ε - AHELM with sigmoid activation function perform efficiently and effectively for the sediment load prediction. In overall, the experimental results clearly exhibit the applicability as well as the usability of the proposed extreme learning machine with asymmetric Huber loss functions. [ABSTRACT FROM AUTHOR]

Delineation of homogeneous reference evapotranspiration (ET0) regions is essential for different applications in hydro‐meteorology. In conventional regionalization approaches, lumped (time‐invariant) statistics such as mean, median or interquartile range of different hydrometeorological variables are often considered as attributes to delineate regions. Information on temporal dynamics of those variables is not utilized (as it is lost in lumped statistics), which if accounted could yield better regions. To address this, a new regionalization approach is presented in fuzzy framework in this Part 1 of a two‐part series. In the proposed approach, information on temporal dynamics of predictor climate variables influencing ET0 is used for regionalization, and the delineated regions are subsequently validated for homogeneity using the predictand (ET0) related information. Effectiveness of the approach is demonstrated through a case study on India, which yielded 18 regions. They are shown to be statistically more homogeneous in ET0 when compared to the existing agro‐ecological zones and regions formed using global fuzzy c‐means clustering method. The homogeneous ET0 regions were found to be different from homogeneous actual evapotranspiration (ETa) regions delineated over India using the fuzzy dynamic clustering approach. Various applications of the homogeneous ET0 regions formed using the proposed approach are presented in Part 2 of this series. [ABSTRACT FROM AUTHOR]

The changes in land use and regional climate together with human interventions affect the hydrological processes, resulting in the spatial and temporal alterations of surface and subsurface flow processes. Both climate and land surface change have adverse implications on the natural hydrological system in terms of variation in the run-off regime, surface storage, evapotranspiration, subsurface flow and infiltration, thereby affecting the hydrology of the river basin as a whole. Even though several studies worldwide have attempted to address the influence of climate change, land-use change and human activities on the hydrology of river basins, either as a whole or limited to a few components of the hydrological cycle, limited attention has been given to study the hydrological changes in the river basins of arid and semi-arid tropics, which are essentially fed by precipitation. The objective of the study is to analyse the changes in hydrological characteristics of the Cauvery river basin, a semi-arid river basin in South India. The changes in the hydrology of the Cauvery river basin are studied by analysing the trends in hydro-meteorological parameters using Mann-Kendall trend tests and Sen's estimator of the slope. The results showed that the changes in the volume of rainfall and the number of rainy days significantly affect the overall hydrological regime of the river basin. The analysis of annual and seasonal rainfall over the Cauvery river basin showed a decreasing trend in the middle Cauvery basin. A declining trend in the number of rainfall events was also observed in the middle Cauvery region. The effect of decreasing trend in the volume of rainfall and number of rainy days is evident from the decreasing trends in the streamflow of the main channel and tributaries of the Cauvery river. The regions of increase in evapotranspiration showed a significant correlation with the regions which exhibited a decline in groundwater level. [ABSTRACT FROM AUTHOR]

Water for irrigation constitutes the highest freshwater demand in any country. For a monsoon-fed country like India, variations in precipitation lead to severe repercussions in the agricultural economy. Water security in India has historically been approached by creating more storage capacity and increasing the supply. Can managing the demand for water be an approach to the challenge of water security? What could be the basis for managing the demand? This article revisits the concepts of virtual water flow and water footprint, to examine their applicability in today's context. The present author has applied the concepts in a dip-stick manner on fruit and sugar export from Maharashtra, India. The quantity of water flowing out of Maharashtra from such exports was assessed. The results show a remarkable quantity of scarce water being diverted to foreign lands. This article also discusses the use of these concepts in water policies to nudge the farmers into making choices appropriate for the region. [ABSTRACT FROM AUTHOR]

The low level tritium, released to marine environment from nuclear facilities, incorporated by marine matrices as tissue free water tritium (TFWT) and organically bound tritium (OBT), was studies for 3 years at Tarapur, situated on the west coast of India. Results show that the tritium concentration in sea water was correlated with TFWT concentration in sea weeds, sediment and marine animals as, with correlation coefficients of 0.6, 0.8 and 0.96 respectively. The TFWT to OBT ratios were observed to be 5.7, 4.9 and 3.6 respectively in seaweed, sediment and marine animals. [ABSTRACT FROM AUTHOR]

The present study is undertaken in the eastern coast of India, along the coastal tract of Bay of Bengal (BoB), to delineate the submarine groundwater discharge (SGD)-borne nutrient flux at temporal scale and their impact to coastal ecology and biogeochemical processes. Solutes chemistry, seepage meter study, stable-isotopic signature, and geophysical techniques were used to identify the surface water–groundwater interaction zone, SGD rate and nutrient flux. The estimated rate of major annual discharge of nutrient fluxes were 240 and 224 mM m−2 day−1 for NO3− and Fetot. The variation of solute and nutrient fluxes was depending on the load of terrestrial water masses, which is triggered by the local monsoonal meteoric recharge. The ecohydrological response to this solute flux results in spatio-temporal patterns of N and P-sensitive algal blooms in the intertidal zones. Most algae were identified as dinoflagellates and some haptophytes, with greenish and brownish hue that provides a distinct look to the coastal landscape. The algal blooms were found to be substantially influenced by the seasonal-nutrients flux and discharge location. Our study is expected to increase the understanding of a rarely reported eco-hydrological response to terrestrial–marine water interactions and their implications in the tropical ocean adjoining the Indian Subcontinent. [ABSTRACT FROM AUTHOR]

Mahanadi River Basin (MRB) is one of the largest tropical pluvial river basin systems in India contributing the major source of freshwater to more than 71 million people in east-central India. Being located in the monsoon "core" region (18–28° N latitude and 73–82° E longitude) and its proximity to Bay of Bengal, Mahanadi River Basin (MRB) system is highly vulnerable to tropical depression-induced severe storms and extreme precipitation-induced fluvial floods during southwest monsoon as reflected in several successive and catastrophic flood episodes in recent years (2001, 2003, 2006, 2008, 2011, 2013, 2014, 2016, 2019). While previous studies so far focused on analyzing either flood trends or frequency and show the role of precipitation in flood generating mechanism over MRB using both instrumental records and climate model simulations, this study for the first time examines space-time coherence in floods and the role catchment wetness in flood response (i.e., magnitude and the timing of floods) over the basin. We examine the incidence of flooding in three different time windows: 1970–2016 (whole 47 years), 1970–2006, and 2007–2016 (post-2007s) using monsoonal maxima peak discharge (MMPD) and peak over threshold (POT) series at 24 stream gauges spatially distributed over the basin. Our analysis reveals the mean dates of floods for most of the gauges are temporally clustered during the month of August irrespective of the type of flood series and the choice of time frames. Further, we observe sensitiveness of runoff responses (flood magnitude, FM and the flood timing, FT) to lagged d-day mean catchment wetness (CW), suggesting a physical association between them. We also note FT is more strongly correlated (as manifested by statistically significant correlations) to CW rather than FM. Overall, we observe, the correlation of CW versus FT is negative, where the flood timing is relatively irregular. The outcomes of the study help to improve the predictability of floods, which can, in turn, enhance existing flood warning techniques. [ABSTRACT FROM AUTHOR]

The present article highlights the need for a clear techno-legal definition of the river floodplains in India. In the context of environment protection, it reviews some of the recent judgements passed by the National Green Tribunal of India (NGT) pertaining to protection of the river floodplains. The inconsistency and differences in the legal arguments pertaining to the definition of river floodplains are highlighted. The geomorphic and hydraulic approach used for defining the floodplain of a river are discussed. It has emerged out from the discussions that the only abiding and faithful definition of the floodplain is its hydro-geomorphic character. This is manifested by sand, silt and clay and various geomorphic units associated with the depositional activity of the present day river. [ABSTRACT FROM AUTHOR]

Water scarcity is a leading concern in both developing and developed nations. Coping with water scarcity requires an understanding of various hydrological processes that act upon precipitation, surface and groundwater at a local scale. We measured isotopic signatures of several water samples from two distinct ecosystems, i.e. tropical savanna in the West and the warm semi-arid region in the East lying across the Western Ghats mountain range, India, to understand the hydrological processes. The results show that the hydrogeological conditions strongly influence the isotopic characteristics of water of different resources, governed by different hydrological processes, even at close spatial scales. Based on the local evaporation lines of different water resources within a particular ecosystem, it is inferred that the water resources are well linked at one site, but have diverse connectivity at the other site. Further, the isotopic signatures of all the water resources are systematically affected by the monsoon precipitation. In addition, anomalously depleted isotopic signatures are observed during known hailstorm events. This may provide a means to trace their signature in the existing water resources. [ABSTRACT FROM AUTHOR]

Palaeoclimatic reconstructions from sediment cores of the Arabian Sea, Bay of Bengal, and other terrestrial ecosystems including lakes, peatlands and proglacial areas from the Indian subcontinent have been used to understand the past Indian Summer Monsoon (ISM) variability. The core monsoon zone (CMZ) of India is one of the most important regions to understand past ISM dynamics. Pollen based palaeoclimatic reconstructions in the CMZ of India suggest a progressive increase in the ISM during the Holocene. However, the results suggesting a weak ISM after the Younger Dryas (YD) cooling event are contrary to the observations made in other parts of the country. Besides this, the minor climatic fluctuations are difficult to find in most of the reconstructions. This may be attributed to poor sample resolution and chronological control. These limitations make it difficult to ascertain whether the response of vegetation to climatic change has been insignificant or whether this change is not reflected in the proxy (proxy response). As a consequence, we argue that pollen based palaeoclimatic reconstructions are one of the most widely used proxies and will be meaningful as backbone for climate models only if the reconstructions become more quantitative. [ABSTRACT FROM AUTHOR]

The eco-geomorphology of the Varanasi Turtle Sanctuary (VTS) located on the Ganga River in Uttar Pradesh, India was examined for its stability using hydraulic geometry of the channels, such as width, depth and discharge acquired from an Acoustic Doppler Current Profiler, and the mapping of planform morphology from remote-sensing images. Planform maps were generated using Corona and Landsat satellite images for the period 1965-2018. The assessment suggests a well-defined, stable cross-section profile along this stretch of the river. It provides conclusive evidence that the geomorphology of the Ganga River within the VTS has remained stable for the past 50 years, except for some minor changes in the form of bar growth and erosion both upstream and downstream of the sanctuary. Construction activities along the bank, movement of large vessels, sand mining in the sanctuary or dredging of the main channel may destabilize the river geomorphology that will negatively affect the integrity of the VTS as well as the ghats at Varanasi. [ABSTRACT FROM AUTHOR]

Urban lakes in many places around the world are rapidly becoming vulnerable because of such factors as urbanization, climate change, anthropogenic pollutant inputs, etc. The influence of such forcing factors on lakes hydrology must be correctly recognized and addressed in order to protect them over the long term. Facing similar challenges, Sukhna Lake, an urban lake in northern India, has apparently dried up frequently in the recent past. Numerous hypotheses were subsequently proposed to isolate the possible factors affecting the lake and its water budget, including the potential impacts of land use changes, climate change, anthropogenic activities and other natural processes. Using meteorological data, lake‐catchment information and a hydrologic model, these hypotheses were comprehensively analysed. Relevant data on rainfall, wind, temperature, lake inflows, groundwater, lake physical characteristics, catchment land uses, soil texture, etc., were gathered for the analysis. A temporal trend analysis of factors relevant to these hypotheses was undertaken to identify critical drivers of hydrological changes. A sensitivity analysis also was performed, using the lake water budget, to determine and prioritize the predominant factors affecting the lake, leading to the creation of an annual lake water budget for the period from 1971 to 2013, highlighting the lake inflows and outflows. The lake annual inflow (catchment run‐off) was computed by adopting a rainfall–run‐off model based on the SCS‐curve number. Lacking any anthropogenic water withdrawals, the outflow was quantified by estimating the evaporation loss (using the FAO‐based Penman–Monteith Equation). The results of the present study  indicate that the process of siltation and the construction of check dams in the catchment, rather than urbanization and climate change, were the dominating reasons contributing to changes in the lake hydrology, and affecting the lake most in recent years. [ABSTRACT FROM AUTHOR]

• The efficiency of SM products to improve unmodelled effects in LSM are examined. • Assimilation of ASCAT and CCI products effectively captures the dynamics of SM. • ASCAT based SM products have high skill to improve LSM simulations. • Blended SM products are more effective to capture the daily SM variability. Realistic representation of surface states using the land surface model (LSM) is extremely challenging owing to human-induced changes and uncertainty in forcing data. In this study, we focus on two crucial objectives pertaining to hydrology namely (a) to understand the ability of different soil moisture (SM) products to improve simulation of unmodeled irrigation processes through data assimilation process, and (b) to learn the feasibility of these SM products to correct the spatial surface soil moisture artifacts caused due to error in precipitation forcing. The utility of SM products evaluated in the present study are retrieved from different satellite sensors and algorithms such as the active satellite-based the Advanced Scatterometer (ASCAT), merged SM from European Space Agency Climate Change Initiative (ESA CCI V4.2) and the latest passive microwave-based SMOS INRA-CESBIO (SMOS-IC) SM product. The results presented for three years (2010, 2011 and 2012) suggest that assimilation of ASCAT and CCI based products effectively captures the SM changes due to irrigation. Similarly, it corrects the spatial artifacts caused due to precipitation errors. However, the single sensor based products have a limitation in spatial samples per day which is critical to capture dynamic SM products over a larger area. Hence, blended products are more effective on a larger area to capture the dynamics in a more effective manner at daily temporal resolutions. [ABSTRACT FROM AUTHOR]

• Synoptic scale observation of water isotopes over high elevations of Western Ghats. • Study reports elevation effect on stable isotope ratio of water in the Western Ghats. • Reports role of humid tropical mountains in controlling seasonal monsoon moisture. • Traces moisture source and mixing processes along highlands of the Western Ghats. • Provides insight into processes controlling regional hydrology in the Western Ghats. • Unravels factors affecting local microclimate to seasonal climate in South India. Forest ecosystem plays a major role in controlling moisture dynamics over the continents, particularly in the humid tropics. The montane forest ecosystem in South India supports a characteristic warm tropical climate which affects the weather pattern and the monsoon system. This study focuses on better understanding of the influence of dual monsoonal rainfall on the surface water and groundwater in south-west India, and the role of the Western Ghats mountain belt in governing the water isotope characteristics (i.e., isotopic elevation, rainfall amount and continental effects) in the humid tropics of South India. This is achieved through a spatial study of stable isotope ratios of surface and subsurface water (oxygen, δ18O and hydrogen, δ2H), collected from different tropical river basins located between Kozhikode (Kerala, 10° 30′ N) and Udupi (Karnataka, 13° 30′ N), in the wettest places and highest peaks of the Western Ghats between 2011 and 2014. The results on stable isotope ratios of ground water, river water and springs show that the water from the tropical mountain belt of the Western Ghats exhibit a low elevation effect with an isotopic lapse rate of 0.09‰/100 m for δ18O up to 2050 m asl. Beyond 2050 m asl, a considerable effect of elevation with an isotopic lapse rate of 2.5‰/100 m for δ18O is observed. The water samples from the Nilgiri ranges (1950–2300 m asl) exhibited higher isotopic lapse rate of 1.5‰/100 m for δ18O unlike that of the mountains (Ezhimala, Agumbe and Chembra) close to the eastern Arabian Sea. The difference in isotopic lapse rate is mainly dependent on (i) the dominating seasonality of oceanic source moisture over the subcontinent leading to higher depletion of heavy isotopes for more inland groundwater during the winter monsoon on the eastern slopes of the Western Ghats (ii) the degree of terrestrial moisture feedback mechanisms along windward slopes of the Ghats belt (i.e., Arabian Sea coast of India) leading to relative enrichment of heavy isotopes in groundwater fed by the highly recycled vapour sources rather than depletion due to amount, elevation or continental effect, and iii) deep cooling of orographically uplifted air moisture at high elevations of inland tropical mountains. The observed isotopic elevation effect on the groundwater and surface water is unique and constrained by specific time scale and mountain ranges within the Western Ghats belt. This study provides new understanding on factors controlling hydrological budget along higher parts of the Western Ghats mountain belt in South India experiencing humid tropical climate. [ABSTRACT FROM AUTHOR]

From the 1980s, Indian summer monsoon rainfall (ISMR) shows a decreasing trend over north and northwest India, and there was a significant observed reduction in July over central and south India in 1982–2003. The key drivers of the changed ISMR, however, remain unclear. It was hypothesized that the large-scale irrigation development that started in the 1950s has resulted in land surface cooling, which slowed large-scale atmospheric circulation, exerting significant influences on ISMR. To test this hypothesis, a fully coupled model, the CESM v1.0.3, was used with a global irrigation dataset. In this study, spatially varying irrigation-induced feedback mechanisms are investigated in detail at different stages of the monsoon. Results show that soil moisture and evapotranspiration increase significantly over India throughout the summertime because of the irrigation. However, 2-m air temperature shows a significant reduction only in a limited region because the temperature change is influenced simultaneously by surface incoming shortwave radiation and evaporative cooling resulting from the irrigation, especially over the heavily irrigated region. Irrigation also induces a 925-hPa northeasterly wind from 30°N toward the equator. This is opposite to the prevailing direction of the Indian summer monsoon (ISM) wind that brings moist air to India. The modeled rainfall in the irrigated case significantly decreases up to 1.5 mm day−1 over central and north India from July to September. This paper reveals that the irrigation can contribute to both increasing and decreasing the surface temperature via multiple feedback mechanisms. The net effect is to weaken the ISM with the high spatial and temporal heterogeneity. [ABSTRACT FROM AUTHOR]

Highlights • Large spatial variation in ecosystem water use efficiency across India. • Higher ecosystem water use efficiency was found in lower Himalayan regions. • Out of 634 districts, only 241 districts were found resilient to dry conditions. • Out of 30 states and UTs, only 10 had more than 50% resilient area. • Forest dominated districts were more resilient, compared to others. Abstract The carbon and water cycles play an important role in ecosystem functioning and are linked to each other through different physical and biological processes. The hydroclimatic disturbances such as droughts affect both hydrological as well as the ecological processes. Increasing hydroclimatic disturbances under climate change will adversely affect the ecohydrological processes and hence, the assessment of the ecohydrological resilience and its controlling factors is important for the sustainability of the ecosystems. In this study, an assessment of the resilience of terrestrial ecosystems in India to hydroclimatic disturbances was carried out at the district (i.e. administrative division) scale. Ecosystem water use efficiency (WUE e), defined as the ratio of net primary productivity (NPP) to evapotranspiration, was used as an indicator of ecosystem functioning or its response to hydroclimatic disturbances. We found a large spatial variation in WUE e in India at district scale, which was significantly higher in lower Himalayan regions compared to rest of the country. Increasing trend in WUE e was found for central parts of the country. The resilience was measured in terms of the ratio of the WUE e under the dry conditions and the mean WUE e , which indicates the ability to absorb hydroclimatic disturbance. Out of 634 districts considered for this study, only 241 (~38%) districts were found resilient to dry conditions, whereas a significant reduction in WUE e was observed for some of the districts. The resilience at district scale indicates the cross-biomes response of ecosystems. In general, the forest dominated districts had higher resilience compared to districts dominated by other biome types. Also, districts having temperate climate were found having higher resilience. Out of 30 states and union territories (UTs) only 10 states had more than 50% resilient area. The results of this study highlight the need for better ecosystem management policies in the country. [ABSTRACT FROM AUTHOR]

The present study analyzes the water quality characteristics of the Ramganga (a major tributary of the Ganga river) using long-term (1991–2009) monthly data and applies the Integrated Catchment Model of Nitrogen (INCA-N) and Phosphorus (INCA-P) to the catchment. The models were calibrated and validated using discharge (1993–2011), phosphate (1993–2010) and nitrate (2007–2010) concentrations. The model results were assessed based on Pearson's correlation, Nash-Sutcliffe and Percentage bias statistics along with a visual inspection of the outputs. The seasonal variation study shows high nutrient concentrations in the pre-monsoon season compared to the other seasons. High nutrient concentrations in the low flows period pose a serious threat to aquatic life of the river although the concentrations are lowered during high flows because of the dilution effect. The hydrological model is satisfactorily calibrated with R 2 and NS values ranging between 0.6–0.8 and 0.4–0.8, respectively. INCA-N and INCA-P successfully capture the seasonal trend of nutrient concentrations with R 2 > 0.5 and PBIAS within ±17% for the monthly averages. Although, high concentrations are detected in the low flows period, around 50% of the nutrient load is transported by the monsoonal high flows. The downstream catchments are characterized by high nutrient transport through high flows where additional nutrient supply from industries and agricultural practices also prevail. The seasonal nitrate (R 2 : 0.88–0.94) and phosphate (R 2 : 0.62–0.95) loads in the catchment are calculated using model results and ratio estimator load calculation technique. On average, around 548 tonnes of phosphorus (as phosphate) and 77,051 tonnes of nitrogen (as nitrate) are estimated to be exported annually from the Ramganga River to the Ganga. Overall, the model has been able to successfully reproduce the catchment dynamics in terms of seasonal variation and broad-scale spatial variability of nutrient fluxes in the Ramganga catchment. [ABSTRACT FROM AUTHOR]

In this paper we identify changes in the Indian Summer Monsoon (ISM) intensity during the late Holocene as revealed by palaeohydrological proxies in the fluvial archives of western India. Proxy indices, including the geomorphological, sedimentological, geochemical and biological evidence along with chronology have been employed to highlight the trend in ISM intensity over the late Holocene. It is inferred that on a longer timescale, the Indian Summer Monsoon weakened during the late Holocene however; short pulses of ameliorated monsoon occurred around 3, 1.6 and 0.3 cal ka BP. Clustering of flood events is seen to occur at 3–2.8, 2.2–1.6, 1.3–1.1 and 0.65–0.2 cal ka BP not necessarily coinciding with strengthening of the ISM. Palaeoflood data with regard to the ISM variability shows that the two most prevalent flood events at 0.5 and 1.7 cal ka BP coincide with the weak monsoon period/climatic transition in this region. The occurrence of high magnitude flood events during weak monsoon periods is also reflected in the modern flood and rainfall data. It is surmised that high magnitude flood events may represent peak monsoon periods however, cannot be singularly considered as indicators for enhanced monsoon conditions in a region. Only a more robust database of palaeohydrological proxies can further validate their implications on the monsoonal changes over western India. [ABSTRACT FROM AUTHOR]

Providing safe and wholesome water in sufficient quantity on a sustainable basis remains elusive for large population especially in semiarid regions and hence water balance estimation is vital to assess water availability in a watershed. The water balance study is formulated to assess the runoff that can be harvested for effective utilization. The study area is Urapakkam watershed with a chain of 3 tanks having an aerial extent of 4.576 km2 with hard rock formation underneath and thus has limited scope for groundwater recharge. Hence surface water is the main water source in this area. Runoff computed for the watershed using USDA-NRCS model varied from 94.95 mm to 2324.34 mm and the corresponding rainfall varied from 575.7 mm to 3608.0 mm, respectively. A simple regression model was developed for the watershed to compute runoff from annual rainfall. Average annual runoff estimated for the watershed was around 37% of the rainfall for the study period from 2000-01 to 2013-14. Statistical analysis and test of significance for runoff obtained by NRCS model and regression model did not show any significant difference thus proving that regression model is efficient in runoff computation for ungauged basins. The volume of water accessible for fifty percent dependable flow year is obtained as 2.46 MCM and even if 50% of it can be effectively harnessed the water available in the watershed is 1.23 MCM. The water demand of the area is estimated as 0.148 MCM for domestic purpose and 0.171 MCM for irrigation purpose, which is much lower than the available runoff that can be harnessed from the watershed. Thus there is scope to harvest 1.23 MCM of water which is more than the demand of the watershed. The study reveals that it is feasible to harvest and manage water effectively if its availability and demand are computed accurately. [ABSTRACT FROM AUTHOR]

A study involving grain size analysis was carried out from the Parsons valley lake deposit, Nilgiris, India to determine the depositional environments and paleoflood events since late Pleistocene period (∼29,838 cal yr BP). A 72 cm lacustrine core was collected from the lake and eight organic rich sediment samples were AMS radiocarbon dated. The study reveals variations in the grain size distribution chiefly influenced by regional climatic conditions. Paleoflood events have been identified by the individual sedimentary flood signatures of varying changes in the magnitude of sediment supply from the background silty sediment matrix around ∼29,838 and ∼8405 cal yr BP. [ABSTRACT FROM AUTHOR]

A cell-to-cell routing (ROU) module has been implemented in a large-scale conceptual hydrological model, developed for the entire landmass of India with a 5 km × 5 km grid cell resolution. The ROU module is based on the principle of time variant spatially distributed direct hydrograph (SDDH) travel time method to route streamflow to the catchment outlet. The integrated model has been calibrated and validated at the Kabini dam flow measurement site over 2001–2006 and 2007–2010, respectively. Nash Sutcliffe Efficiency (NSE) is found to be 0.55 and 0.47 for the calibration and the validation period, respectively. The obtained NSE value shows that the model is satisfactorily calibrated and ROU module compliments the other modules. The comparison between model simulation results with implemented and original routing schemes show that implemented method, with modified parameterization, outperforms the original one. The overall results support the applicability of the implemented routing scheme. [ABSTRACT FROM AUTHOR]

High resolution reconstructions of the India Summer Monsoon (ISM) are essential to identify regionally different patterns of climate change and refine predictive models. We find opposing trends of hydrological proxies between northern (Sahiya cave stalagmite) and central India (Lonar Lake) between 100 and 1300 CE with the strongest anti-correlation between 810 and 1300 CE. The apparently contradictory data raise the question if these are related to widely different regional precipitation patterns or reflect human influence in/around the Lonar Lake. By comparing multiproxy data with historical records, we demonstrate that only the organic proxies in the Lonar Lake show evidence of anthropogenic impact. However, evaporite data (mineralogy and δ 18 O) are indicative of precipitation/evaporation (P/E) into the Lonar Lake. Back-trajectories of air-mass circulation over northern and central India show that the relative contribution of the Bay of Bengal (BoB) branch of the ISM is crucial for determining the δ 18 O of carbonate proxies only in north India, whereas central India is affected significantly by the Arabian Sea (AS) branch of the ISM. We conclude that the δ 18 O of evaporative carbonates in the Lonar Lake reflects P/E and, in the interval under consideration, is not influenced by source water changes. The opposing trend between central and northern India can be explained by (i) persistent multidecadal droughts over central India between 810 and 1300 CE that provided an effective mechanism for strengthening sub-tropical westerly winds resulting in enhancement of wintertime (non-monsoonal) rainfall over northern parts of the Indian subcontinent, and/or (ii) increased moisture influx to northern India from the depleted BoB source waters. [ABSTRACT FROM AUTHOR]

Women face greater challenges than men in accessing water, sanitation, and hygiene (WASH) resources to address their daily needs, and may respond to these challenges by adopting unsafe practices that increase the risk of reproductive tract infections (RTIs). WASH practices may change as women transition through socially-defined life stage experiences, like marriage and pregnancy. Thus, the relationship between WASH practices and RTIs might vary across female reproductive life stages. This cross-sectional study assessed the relationship between WASH exposures and self-reported RTI symptoms in 3,952 girls and women from two rural districts in India, and tested whether social exposures represented by reproductive life stage was an effect modifier of associations. In fully adjusted models, RTI symptoms were less common in women using a latrine without water for defecation versus open defecation (Odds Ratio (OR) = 0.69; Confidence Interval (CI) = 0.48, 0.98) and those walking shorter distances to a bathing location (OR = 0.79, CI = 0.63, 0.99), but there was no association between using a latrine with a water source and RTIs versus open defecation (OR = 1.09; CI = 0.69, 1.72). Unexpectedly, RTI symptoms were more common for women bathing daily with soap (OR = 6.55, CI = 3.60, 11.94) and for women washing their hands after defecation with soap (OR = 10.27; CI = 5.53, 19.08) or ash/soil/mud (OR = 6.02; CI = 3.07, 11.77) versus water only or no hand washing. WASH practices of girls and women varied across reproductive life stages, but the associations between WASH practices and RTI symptoms were not moderated by or confounded by life stage status. This study provides new evidence that WASH access and practices are associated with self-reported reproductive tract infection symptoms in rural Indian girls and women from different reproductive life stages. However, the counterintuitive directions of effect for soap use highlights that causality and mechanisms of effect cannot be inferred from this study design. Future research is needed to understand whether improvements in water and sanitation access could improve the practice of safe hygiene behaviors and reduce the global burden of RTIs in women. [ABSTRACT FROM AUTHOR]

Koyna-Warna Region (KWR) is one of the known sites for reservoir triggered seismicity. The continued triggered seismicity over the five decades is restricted to a region of about 600-700 sq. km, which provides a unique opportunity to monitor geophysical anomalies likely to be associated with seismicity of the region. Present study confers temporal gravity changes recorded by gPhone and GRACE satellite and interprets observed changes in conjunction with seismological, geodetic (cGPS) observations and groundwater level measurements. GRACE data suggest that seasonal vertical deformation due to hydrological loading is ∼ 2 cm, which corroborates with continuous GPS observations. Seasonal hydrological loading of the region, which is in a phase of reservoir loading, might be influencing the critically stressed KWR leading to the seasonal seismicity of the region. The gPhone gravity data distinctly show co-seismic gravity signals for eight earthquakes of M > 2 and gravity anomalies show positive correlation on a logarithmic scale with earthquake released energy. To investigate the cause of gravity changes, an estimate is made for 14 April 2012 earthquake for M 4.8 using fault dislocation model. The recorded gravity changes of 189 μGal by gPhone located at a distance of 28 km from the hypocentre is much more than the estimate of ∼0.1 μGal calculated for M 4.8 Koyna earthquake. Therefore, it is inferred that co-seismic gravity signals for eight earthquakes are primarily caused due to redistribution of mass at shallow depth. [ABSTRACT FROM AUTHOR]

Indian agriculture relies on monsoon rainfall and irrigation from surface and groundwater. The interannual variability of monsoon rainfalls is high, which forces South Indian farmers to adapt their irrigated areas to local water availability. In this study, we have developed and tested a methodology for monitoring these spatiotemporal variations using Sentinel-1 and -2 observations over the Kudaliar catchment, Telangana State (~1000 km²). These free radar and optical data have been acquired since 2015 on a weekly basis over continental areas, at a high spatial resolution (10-20 m) that is well adapted to the small areas of South Indian field crops. A machine learning algorithm, the Random Forest method, was used over three growing seasons (January to March and July to November 2016 and January to March 2017) to classify small patches of inundated rice paddy, maize, and other irrigated crops, as well as surface water stored in the small reservoirs scattered across the landscape. The crop production comprises only irrigated crops (less than 20% of the areas) during the dry season (Rabi, December to March), to which rain-fed cotton is added to reach 60% of the areas during the monsoon season (Kharif, June to November). Sentinel-1 radar backscatter provides useful observations during the cloudy monsoon season. The lowest irrigated area totals were found during Rabi 2016 and Kharif 2016, accounting for 3.5 and 5% with moderate classification confusion. This confusion decreases with increasing areas of irrigated crops during Rabi 2017. During this season, 16% of rice and 6% of irrigated crops were detected after the exceptional rainfalls observed in September. Surface water in small surface reservoirs reached 3% of the total area, which corresponds to a high value. The use of both Sentinel datasets improves the method accuracy and strengthens our confidence in the resulting maps. This methodology shows the potential of automatically monitoring, in near real time, the high short term variability of irrigated area totals in South India, as a proxy for estimating irrigated water and groundwater needs. These are estimated over the study period to range from 49.5 ± 0.78 mm (1.5% uncertainty) in Rabi 2016, and 44.9 ± 2.9 mm (6.5% uncertainty) in the Kharif season, to 226.2 ± 5.8 mm (2.5% uncertainty) in Rabi 2017. This variation must be related to groundwater recharge estimates that range from 10 mm to 160 mm·yr-1 in the Hyderabad region. These dynamic agro-hydrological variables estimated from Sentinel remote sensing data are crucial in calibrating runoff, aquifer recharge, water use and evapotranspiration for the spatially distributed agro-hydrological models employed to quantify the impacts of agriculture on water resources. [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]

Evidence has suggested a wetting trend over part of the Tibetan Plateau (TP) in recent decades, although there are large uncertainties in this trend due to sparse observations. Examining the change in the moisture source for precipitation over a region in the TP with the most obvious increasing precipitation trend may help understand the precipitation change. This study applied the modified Water Accounting Model with two atmospheric reanalyses, ground-observed precipitation, and evaporation from a land surface model to investigate the change in moisture source of the precipitation over the targeted region. The study estimated that on average more than 69% and more than 21% of the moisture supply to precipitation over the targeted region came from land and ocean, respectively. The moisture transports from the west of the TP by the westerlies and from the southwest by the Indian summer monsoon likely contributed the most to precipitation over the targeted region. The moisture from inside the region may have contributed about 18% of the total precipitation. Most of the increased moisture supply to the precipitation during 1979-2013 was attributed to the enhanced influx from the southwest and the local moisture supply. The precipitation recycling ratio over the targeted region increased significantly, suggesting an intensified hydrological cycle. Further analysis at monthly scale and with wet-dry-year composites indicates that the increased moisture contribution was mainly from the southwest and the targeted region during May and September. The enhanced water vapor transport from the Indian Ocean during July and September and the intensified local hydrological recycling seem to be the primary reasons behind the recent precipitation increase over the targeted region. [ABSTRACT FROM AUTHOR]

Frequent recurrences of drought in India have had major societal, economical, and environmental impacts. While region-specific assessments are abundant, exhaustive appraisal over large spatial scales has been insubstantial. Here a new drought index called Water Storage Deficit Index (WSDI) is devised and analyzed for holistic representation of drought. The crux of the method is the employment of terrestrial water storage (TWS) variations from Gravity Recovery and Climate Experiment (GRACE) for quantification of drought intensity and severity. Drought events in recent times are well identified and quantified using the approach over four homogenous rainfall regions of India over the period from April 2002 to April 2015. Among the four regions, the highest peak deficit of −158.00 mm is observed in January 2015 over central India. While the drought of 2002-04 is prominent in peninsular and west-central India, the drought of 2009-10 and 2012-13 is conspicuous in almost all four regions of India. The longest deficit period of 23 months (from February 2009 to December 2010) and the highest severity value of −26.31 are observed in central and northwestern India, respectively. WSDI values show an increasing trend in west-central India (0.07 yr−1), indicating recovery from previously existing drought conditions. On the contrary, a decreasing trend in WSDI is observed in northwestern (−0.07 yr−1) and central (−0.18 yr−1) India. Results demonstrate considerable confidence in the potential of WSDI for robust characterization of drought over large spatial scales. [ABSTRACT FROM AUTHOR]