RAAJ Ramsankaran

• PhD
• Professor (Full) at Indian Institute of Technology Bombay

In recent years, glacial lake outburst flood (GLOF) hazards in the Himalayan region have garnered considerable attention. The expansion of glacial lakes and the corresponding increase in volume play major roles in the initiation of GLOFs. Due to the lack of systematic assessments and the challenges associated with conducting field surveys, communit...

Snow depth (SD) exhibits high spatiotemporal heterogeneity in Western Himalaya (WH), and its knowledge is essential for applications related to water resources, disaster management, climate, etc. However, due to inclement weather and rugged topographical conditions, only a sparse network of SD monitoring stations exists in WH. Spaceborne passive mi...

Rock glaciers, important indicators of mountain permafrost, play a critical role in mountain hydrology. Despite their significance, comprehensive studies on delineation, characterization, and hydrological potential of rock glaciers in the Himalayan region are currently in the incipient stages. In this study, we present a detailed rock glacier inven...

Snow depth (SD) exhibits high spatiotemporal heterogeneity in Western Himalaya (WH), and its knowledge is essential for applications related to water resources, disaster management, climate, etc. However, due to inclement weather and rugged topographical conditions, only a sparse network of SD monitoring stations exists in WH. Spaceborne passive mi...

Assessing runoff under changing land use/land cover (LULC) and climatic conditions is crucial for achieving effective and sustainable water resource management on a global scale. In this study, the focus was on runoff predictions across three diverse Indian watersheds—Wunna, Bharathapuzha, and Mahanadi—spanning distinct agro-climatic zones to captu...

Snow-induced disasters pose significant risks in mountainous regions. Accurate visibility assessment is crucial for informed decision-making and disaster preparedness. This paper presents an innovative approach that integrates theoretical literature with practical application using augmented reality (AR) to address this challenge. The proposed syst...

In his paper we model the evolution of the exposure of the Lower Barun lake (located in the Nepal Himalaya) to avalanches from the surrounding susceptible slopes under various SSP scenarios. We used numerical ice-flow modelling for this purpose.

Indian heritage structures display exceptional detail, adorned with numerous sculptures that offer insights into the nation's diverse cultural heritage and artistic legacy. Most of the regions in India are in seismically active zones; therefore, seismic assessment of heritage structures is essential for identifying structural weaknesses, potential...

Global warming causes glacial mass loss, leading to the growth of high-mountain glacial lakes. The presence of glacial lakes poses a significant threat to downstream communities, as they can produce destructive Glacial Lake Outburst Floods (GLOFs). Timely basin-scale inventory and GLOF susceptibility assessments are crucial, considering past GLOF e...

Hydrological models are widely used to estimate and forecast streamflow for various applications. Given the inherent uncertainties in these models, there is a pressing need to enhance the current state of the modelling strategies. Historically, hydrological models showed significant improvement through soil moisture (SM) assimilation. Particularly,...

The prevalent climate warming across the mountain regions worldwide has exacerbated the snow melt, glacier recession and permafrost thawing that is impacting the hydrological cycle. The rock glaciers, a manifestation of ice-rich permafrost, could be regionally important for sustaining the streamflow, especially in the lean season in the Himalaya. S...

Spatiotemporal snow depth (SD) mapping in the Indian Western Himalayan (WH) region is essential in many applications pertaining to hydrology, natural disaster management, climate, etc. In situ techniques for SD measurement are not sufficient to represent the high spatiotemporal variability in SD in the WH region. Currently, low-frequency passive mi...

Evolution of glacial lakes in the Himalayan and Karakoram (H-K) mountain ranges is an important indicator of glacier changes in response to climatic warming. The study utilized multi-temporal Landsat 4, 5, 7, and 8 images accessible in the cloud-based Google Earth Engine platform to analyse the spatiotemporal variations of the supraglacial lake (SG...

This study presents a reconstruction of basin scale long-term annual surface mass balance (SMB) estimates for 91 glaciers (≥ 1 km²) of Chandra basin in Western Himalayas from 1989 to 2020. The presented approach requires three inputs: annual Equilibrium Line Altitude (ELA), long-term average mass balance, and an estimate of mass balance gradient ac...

Supraglacial debris influences the glacier-climate relationship by altering the ablation patterns of the debris-covered glaciers. The intricate surface morphology of debris-covered glaciers renders difficulties in their assessment through satellite remote sensing alone. In this context, unmanned aerial vehicles (UAVs) have the advantage of providin...

Spatiotemporal snow depth (SD) mapping in the Indian Western Himalayan (WH) region is essential in many applications pertaining to hydrology, natural disaster management, climate, etc. In-situ techniques for SD measurement are not sufficient to represent the high spatiotemporal variability of SD in WH. Currently, low-frequency passive microwave (PM...

The Global Vipassana Pagoda is the largest meditation hall in the world, located near Gorai, north west of Mumbai, Maharashtra, India. Although the monument's artistic integrity is still somewhat intact, material degradation and structural deformations are observed. The visual inspections of such monuments are the primary and most important practic...

Glacial lake outburst floods (GLOFs) are a severe threat to communities in the Himalayas; however, GLOF mitigation strategies have been implemented for only a few lakes, and future changes in hazard are rarely considered. Here, we present a comprehensive assessment of current and future GLOF hazard for Gepang Gath Lake, Western Himalaya, considerin...

Monitoring snowpack depth is essential in many applications at regional and global scales. Space-borne passive microwave (PMW) remote sensing observations have been widely used to estimate snow depth (SD) information for over four decades due to their responsiveness to snowpack characteristics. Many approaches comprised of static and dynamic empiri...

In this study, we simulated the evolution of a large glacier-fed lake called the Gepan Gath lake located in Western Himalayas by numerically modelling the evolution of the Gepan Gath glacier that feeds the lake. Due to the extremely large volume and steep lake sidewalls, the lake has been classified as ‘critical’ or prone to hazards such as lake ou...

This study aims to demonstrate the capability of a low-cost echosounder for measuring the depths of high-altitude glacial lakes. A pilot survey was conducted in a shallow glacial lake associated with the Drang Drung glacier located in the Zanskar region of Ladakh, India. A bathymetric survey was carried out using Airmar P66 echosounder mounted on t...

Snow depth (SD) knowledge is significant in many applications related to hydrology, climate, and disaster management. Many snow depth (SD) models are developed using multifrequency spaceborne passive microwave (PMW) brightness temperature (Tb) observations because of their sensitivity to SD. The sensitivity of Tb to SD is affected by snow metamorph...

The use of accurate streamflow estimates is widely recognized in the hydrological field. However, due to the model’s structural error, they often yield suboptimal streamflow estimates. Past studies have shown that soil moisture assimilation improves the performance of the hydrological model which often results in enhanced model estimates. Due to th...

Catchment hydrological response to anthropogenic change is quite extensive. Especially, surface runoff is highly dependent on various human-induced activities like urban sprawl, construction of dams, modern agricultural practices, etc. Hence, understanding its impact is highly essential. In this study, a heterogeneous river basin called Bharathapuz...

Climate change (CC) affects millions of people directly or indirectly. Especially, the effect of CC on the hydrological regime is extensive. Hence, understanding its impact is highly essential. In this study, the Bharathapuzha river basin (BRB) lying in the Western Ghats region of southern India is considered for CC impact assessment, as it is a hi...

Total water storage change (TWSC) reflects the balance of all water fluxes in a hydrological system. The Gravity Recovery and Climate Experiment/Follow-On (GRACE/GRACE-FO) monthly gravity field models, distributed as spherical harmonic (SH) coefficients, are the only means of observing this state variable. The well-known correlated noise in these o...

Floods are the most commonly occurring natural disaster, with the Centre for Research on the Epidemiology of Disasters 2021 report on “The Non-COVID Year in Disasters” estimating economic losses worth over USD 51 million and over 6000 fatalities in 2020. The hydrodynamic models which are used for flood forecasting need to be evaluated and constrain...

Floods are the most commonly occurring natural disaster, with the Centre for Research on the Epidemiology of Disasters 2021 report on “The Non-COVID Year in Disasters” estimating economic losses worth over USD 51 million and over 6000 fatalities in 2020. The hydrodynamic models which are used for flood forecasting need to be evaluated and constrain...

In this study, we simulated the evolution of a large glacier-fed lake called the Gepangath lake located in Western Himalayas by numerically modelling the evolution of the Gepangath glacier that feeds the lake. This modelling was carried out by a 1D model that is based on the principle of mass conservation. The 1D model was forced with the glacier s...

The Himalaya plays a vital role in regulating the freshwater availability for nearly a billion people living in the Indus, Ganga, and Brahmaputra River basins. Due to climate change and constantly evolving human-hydrosphere interactions, including land use/cover changes, groundwater extraction, reservoir or dam construction, water availability has...

Glacier surface velocity is an important variable for glacier dynamics studies. Estimation of accurate surface velocity from remote sensing is a challenge, especially for glaciers with no in-situ observations. To overcome this challenge, a new method for glacier feature tracking named as Spatially varying WIndow based maximum likelihood Feature Tra...

Background Drought is a recurrent phenomenon emerging from an inter-annual and intra-seasonal deficit of water across the atmosphere-to-aquifer continuum and these events are reported to be very severe in regions of Ethiopia. Availability of accurate precipitation observations significantly impacts the drought monitoring systems. These observations...

Streamflow is one of the key variables in the hydrological cycle. Simulation and forecasting of streamflow are challenging tasks for hydrologists, especially in sparsely gauged areas. Coarse spatial resolution remote sensing soil moisture products (equal to or larger than 9 km) are often assimilated into hydrological models to improve streamflow si...

Total Water Storage Change (TWSC) reflects the balance of all water fluxes in a hydrological system. The Gravity Recovery and Climate Experiment/Follow-On (GRACE/GRACE-FO) satellite missions are the only means of observing this state variable, distributed as coefficients of a spherical harmonic (SH) model. The well-known correlated noise in these o...

The need for and the use of different data assimilation techniques to improve the quality of streamflow forecast is now well established. In this paper, the goal is to demonstrate the power of a new class of methods known as the Forward Sensitivity Method (FSM) which is based on the temporal evolution of model sensitivities with respect to the cont...

The accuracy of streamflow forecasts is important for efficient monitoring and mitigation of flood events. Unfortunately, the uncertainty in the model control variable which includes model parameters, initial and boundary conditions, propagates through the model, resulting in the degradation of streamflow forecast. Various studies in the past have...

Abstract: The climate emergency has exacerbated catastrophic flooding and put an unprecedented number of people at risk. Accurate information on flood inundation is therefore critical to bolster preparedness and reduce flood related losses. Satellite-based Synthetic Aperture Radar (SAR) sensors with all-day/all-weather imaging capabilities, provide...

In the Himalayas, rising number of glacial lakes with increase in area of existing lakes is a matter of serious concern and correct mapping is an important step towards regular monitoring of these glacial lakes. This study used Double Window Flexible Pace Search method to identify an optimal threshold of Normalized Difference Water Index value on m...

This study presents a recent estimate (for year 2017) of ice thickness and volume of a small glacier called Patsio Glacier located in Western Himalayas. Also, the present study aims to examine whether the improvement in GlabTop2 based estimates obtained for Chhota Shigri Glacier through the use of relatively accurate and high-resolution Digital Ele...

In this study, glacier ice thickness distribution and storage volume has been modelled for two glaciers viz., Vestre Broggerbreen and Feiringbreen situated across the Kongsfjorden around Ny-Ålesund in Svalbard. These two high Arctic glaciers are being monitored through the ongoing efforts of the Indian Arctic Program. Here, the capability of a glac...

Indian cities face unplanned and rapid urbanization, yet limited studies investigate their urban growth dynamics systematically. Urban land density (ULD) analysis is crucial for developing countries worldwide, especially for populous countries like India. To understand the complexities of urban structure and its expansion, we propose a framework fo...

Snow Depletion Curve derived from satellite images is a key parameter in Snowmelt Runoff Model. The fixed temporal resolution of a satellite and presence of cloud cover in Himalayas restricts accuracy of generated SDC. This study presents an effective approach of reducing temporal interval between two consecutive dates by integrating normalized Sno...

Supraglacial debris complicates automated and semi‐automated mapping of glacier terrains in the Greater Himalayan Range, an area recognized for contrasting signals of its glaciers toward climate change. Despite exhibiting such fluctuating behavior of glaciers, the Greater Himalayan Range lacks literature on mapping of its glaciers. In this rugged a...

Timely measurement of precipitation across a large area is essential for flood/drought/landslide forecasting. Satellite-based precipitation estimates (SPEs) are one of the promising sources of precipitation data for the above mentioned near real-time (NRT) applications. However, these estimates have inherent errors and uncertainty. Hence, it is cru...

Accurate flood inundation forecasts have the potential to minimize socioeconomic losses, but uncertainties in inflows propagated from the precipitation forecasts result in large prediction errors. Recent studies suggest that by assimilating independent flood observations, inherent uncertainty in hydraulic flood inundation modelling can be mitigated...

Satellite observations of flood inundation have the potential to increase the reliability and accuracy of flood forecasts, thereby contributing to improved flood resilience of vulnerable populations. However, new generation high-resolution satellites can only observe small portions of large river systems river during a flood. Since, the model-data...

Real-time streamflow modeling is a challenging endeavor in regions where real-time ground-based hydro-meteorological observations are scarce. Nevertheless, with the emergence of satellite remote sensing, some of the essential hydro-meteorological datasets such as rainfall and soil moisture are available in near real-time, which can circumvent the p...

Role of Unmanned Aerial Vehicle (UAV)-based remote sensing (RS) applications in glaciology have increased in recent years. UAV-based RS studies on mountain glaciers are mainly focussing on obtaining accurate ultra-high-resolution data from UAV images for different glaciological applications. However, studies understanding the challenges involved du...

Knowing the ice thickness distribution of a glacier is of fundamental importance for a number of applications, ranging from the planning of glaciological fieldwork to the assessments of future sea-level change. Across spatial scales, however, this knowledge is limited by the paucity and discrete character of available thickness observations. To obt...

Accurately simulating floodplain inundation is absolutely vital to minimize damage to life and property. The giant strides made in advanced computing, now allow running increasingly complex models at reasonable resolutions over large areas, with the promise of further improvement in the near future. However, the uncertainty contributed by input, bo...

Timely measurement of precipitation across large area is essential for flood/drought/landslide forecasting. Satellite-based precipitation estimates (SPEs) are one of the promising sources of precipitation data for the above mentioned near real time (NRT) applications. However, these estimates have inherent errors and uncertainty. Hence, it is cruci...

Disappearance of mountain glaciers and formation/expansion of glacial lakes are among the most distinguishable and dynamic impacts of climate warming in the Himalayas. The present research focuses on the identification of potential sites for future lake formation in the 65 selected study glaciers of Chandra basin located in the western Himalayas. T...

High-resolution sea surface temperature (SST) estimates are dependent on satellite-based infrared radiometers, which are proven to be highly accurate in the past decades. However, the presence of clouds is a big stumbling block when physical approaches are used to derive SST. This problem is more prominent across tropical regions such as Arabian Se...

This article reports modeled ice thickness distribution and total ice volume of the 65 selected glaciers (>0.5 km2) of Chandra basin, located in the Western Himalayas. This is a first-of-its-kind study that gives detailed insights about the current ice thickness distribution at an individual glacier level in the Western Himalayas. The estimates are...

Floods can have extremely expensive and often fatal consequences, thereby necessitating accurate flood inundation forecasts for increased preparedness and resilience. In an operational forecasting scenario, inflow uncertainties propagated from precipitation forecasts dominate and lead to inherently erroneous predictions of flood inundation, frequen...

Unmanned Aerial Vehicle (UAV) based remote sensing (RS) studies in glaciology are mainly focusing on obtaining accurate high-resolution data from UAV images. Studies for identifying and minimising the challenges faced during the UAV-based RS data acquisition survey on inaccessible and harsh terrains of mountain glaciers is limited. This study aims...

Green spaces are an integral part of urban landscape and offer numerous benefits related to quality of urban life. However, due to various factors, the distribution of green spaces among city neighbourhoods is often skewed. Hence, urban planners require effective tools to routinely map and monitor the greening/ un-greening phenomena among the neigh...

Near-real-time (NRT) satellite-based rainfall estimates (SREs) are a viable option for flood/drought monitoring. However, SREs have often been associated with complex and nonlinear errors. One way to enhance the quality of SREs is to use soil moisture information. Few studies have indicated that soil moisture information can be used to improve the...

The agricultural productivity of India is largely affected by land degradation and water scarcity, causing huge economic losses. Traditionally, this is overcome through Integrated Watershed Management Programme (IWMP), but this approach is restricted to few areas due to limited resources. Therefore, prioritisation is a crucial step in planning wate...

Sea surface temperature (SST) is a fundamental physical variable for understanding, quantifying and predicting complex interactions between the ocean and the atmosphere. Such processes determine how heat from the sun is redistributed across the global oceans, directly impacting large- and small-scale weather and climate patterns. The provision of d...

Glaciers in the Himalaya are retreating, due to climate change. Retreating glaciers can cause formation of lakes due to over-deepening of bottom topography. It can lead to disastrous events in the glaciated terrain due to flash flood. Therefore, to mitigate such catastrophic events, a semi-automated tool is developed to estimate glacier thickness,...

Studies have demonstrated the potential of Synthetic Aperture Radar (SAR) based Flood Extent Assimilation (FEA) for improving flood forecasting accuracy. As the number of high-resolution SAR sensors increases, the likelihood of observing flood events from space also increases. This implies that for ungauged catchments where information about model...

Accurate forecasts are a necessity in a world with frequent flood disasters and climatic anomalies. Studies have demonstrated that one of the primary sources of uncertainty in flood modelling is, the topographic input data, the bathymetry in particular. As high-resolution elevation/bathymetry datasets are often unavailable in developing regions, th...

Continuous availability of a variety of satellite and reanalysis rainfall products have triggered the use of such products as an alternate source of rainfall data in sparsely gauge networked areas. However, before utilizing them a detailed validation of these datasets are essential to have some level of guarantee. In many parts of Africa in general...

The Himalayas, which has the highest concentration of glaciers outside the poles, form a huge reservoir of fresh water. These glaciers are not only important because of the contribution they make to our water resources, but also because they are a great help in understanding the effects of climate change. However, monitoring even a few of these gla...

Recent studies have demonstrated the potential of assimilating flood extents derived from Synthetic Aperture Radar (SAR) imagery for improved flood forecasts. The increasing number of high resolution SAR sensors which provide a partial coverage of flooded areas can benefit from knowledge on the impacts of spatial location on the reduction of foreca...

Urban Green Spaces (UGS) offer social and environmental benefits that enhance quality of life of the residents. However, due to the underlying social and economic disparities, different sections of urban population have disproportionate level of access to UGS. The environmental inequity owing to the varied UGS distribution poses a challenge to urba...

In line with the increasing scientific interest on the Himalayan glaciers , this study focuses on estimating a long-term annual surface mass balance time series of the Chhota Shigri glacier, a 'benchmark' glacier in the western Himalayas. The approach used here is based on the fact that the annual glacier-wide surface mass balance can be deduced fr...

The present study investigates the potential of coupled Soil Moisture Analytical Relationship (SMAR) and Ensemble Kalman Filter (EnKF) based surface soil moisture data assimilation for improving the streamflow simulations. For this purpose, synthetic and real data assimilation experiments were carried out using Soil and Water Assessment Tool (SWAT)...

Synthetic Aperture Radar (SAR) data are currently the most reliable resource for flood monitoring, though still subject to various uncertainties, which can be objectively represented with probabilistic flood maps. Moreover, the growing number of SAR satellites has increased the likelihood of observing a flood event from space through at least a sin...

Synthetic aperture radar (SAR) sensors have emerged as the preferred mode of flood monitoring due to their all‐weather, all‐day imaging capabilities. Current and upcoming SAR satellites provide high‐resolutions and shorter revisit times, which can facilitate effective resource allocation during emergency response. However, the sensitivity of microw...

Estimation of glacier ice-thickness distribution is important for many glacio-hydrological applications such as runoff projections, glacial lake outburst flood (GLOF) predictions, future evolution of glaciers. Varieties of modelling approaches are available for estimating ice-thickness distribution depending upon the data availability. In the prese...

Considering the importance of the error estimates for satellite rainfall products in various applications, the present article deals with the development of an Error Model for Modified-INSAT Multi-Spectral Rainfall Algorithm (M-IMSRA) Estimates (EMME), a recently developed climate region scale rainfall algorithm across India. A non-parametric frame...

The present study demonstrates a spatially distributed application of field-scale annual soil loss model the modified-MMF (MMMF) to a large watershed using hydrological routing techniques, remote sensing data and geospatial technologies. In this study, the MMMF model is implemented after incorporating the corrections suggested in recent literature...

The present study assesses the effect of accounting the temporal variation of near-surface lapse rate in the conceptual, degree-day snowmelt runoff model simulations in a cold-desert region of Himalayas. The near-surface lapse rate over Spiti basin shows seasonal variation during a year. The results obtained show that the inclusion of monthly varia...

Synthetic Aperture Radar (SAR) data are currently the most reliable resource for flood monitoring, though still subject to various uncertainties, which can be objectively represented with probabilistic flood maps. Moreover, the growing number of SAR satellites has increased the likelihood of observing a flood event from space through at least a sin...

The main objective of this study is to validate and inter-compare two Near-Real-Time Satellite Rainfall Estimates (NRT-SREs): INSAT Multispectral Rainfall Algorithm (IMSRA, simple blended product) and TMPA 3B42-RT V7 (3B42-RT, multisatellite product) across India. This study aims to provide some insight into the error characteristics of both the NR...

Drought is a recurrent phenomenon in the arid and semi-arid regions of Ethiopia. In the past two decades, millions of people are affected by drought throughout the country. To assess and monitor droughts, accurate rainfall record is crucial at different spatial and temporal scales. However, rain gauges are sparsely distributed across Ethiopia. To o...

In this study, an Artificial Neural Network (ANN) based modelling has been done to estimate daily Sea Surface Temperature (SST) using Moderate Resolution Imaging Spectroradiometer (MODIS) Aqua datasets. A feed-forward Back-Propagation Artificial Neural Network (ANN-BP) model is implemented in this work. This ANN based SST model (MODIS-SSTANN) was t...

The lack of necessary policy interventions in the cities of the developing countries result in a disproportionate distribution of Urban Green Spaces (UGS), a key component of urban landscape. The socioeconomically affluent neighbourhoods are known to possess a better share of UGS arranged in distinctive spatial patterns. Studies relating SocioEcono...

This article presents a study carried out using EnKF based assimilation of coarser-scale SMOS soil moisture retrievals to improve the streamflow simulations and forecasting performance of SWAT model in a large catchment. This study has been carried out in Munneru river catchment, India, which is about 10,156 km². In this study, an EnkF based new ap...