Himalayan Glaciers Research Articles

Observations of black carbon and albedo over a Central Himalayan Glacier (Satopanth): Preliminary results

Simultaneous measurements of ambient atmospheric black carbon (BC) mass concentrations and radiative fluxes were carried out over Satopanth glacier in the central Himalayas from September 22 to October 2, 2016, as a part of a glacier campaign experiment. The daily mean atmospheric BC concentrations varied between 165 ± 20–263 ± 32 ng m−3 with a mean of 199 ± 54 ng m−3 during the observational period. The measured average surface albedo was found to be 0.24 ± 0.11 during the entire period of observation. Spectral albedo from Moderate Resolution Imaging Spectroradiometer - Bidirectional Reflectance Distribution Function (MODIS-BRDF) satellite observation and net radiometer derived glacier albedo was found to be in good agreement with a correlation of 0.64 over the region. Concentration weighted trajectory analysis (CWT) over the site indicates a 70% BC transport from the Indo-Gangetic plain, Pakistan, and the Middle East region. BC radiative forcing was estimated using an optical model along with a radiative transfer model. An average BC direct radiative forcing of −5.4 ± 0.25 W m−2 and 2.4 ± 0.19 W m−2 was found respectively in the surface and at the top of the atmosphere (TOA) during the experimental period. The estimated average BC induced heating rate was found to be 0.33 ± 0.04 K day−1over the region.

Suspended sediment dynamics and associated hydro-meteorological interrelations in east rathong glacier, eastern himalaya, india

The records of suspended sediments and associated hydro-meteorology of the glacierized catchments are very limited in Sikkim Himalaya. Therefore, we carried out the first-ever estimate of suspended sediment transport from the meltwater stream of East Rathong Glacier for June-September during three consecutive melt seasons (2013–2015). These records were used to estimate the suspended sediment concentration (SSC), load (SSL), yield (SSY) and erosion rate (ER). The daily mean SSC was 105.75, 84.20, and 91.51 mg/l during melt seasons of 2013–2015 respectively. The monthly mean SSC of the combined melt season of 2013–2015 was 92.72, 107.14, 105.93 and 60.46 mg/l for June-September, respectively. The observation shows that July-August contributed to maximum SSC, accounting 70.45% of total SSC. Similarly, the monthly mean SSL for June-September was 55.64, 69.61, 65.75 and 25.72 tons, respectively. We observed high variability in SSL (CV = 0.54) than SSC (CV = 0.38) since the estimation of SSL depends on both discharge (Q) and SSC. The relationship between monthly mean SSC and Q was highly significant (R2 = 0.98) than daily SSC and Q (R2 = 0.25) due to reduced variability on a monthly scale. Further, mean SSY in the catchment was high during peak melting season (July-August), which substantially reduced during the end of the melting season. We estimated the mean SSY of 281.93 ton/yr km2 during the combined melt season (2013–2015). The average ER for the East Rathong Glacier basin was 1.04 mm/yr, which is lower than the ER of most of the Himalayan glaciers. We observed significant meteorological control of Tmean, Tmax and Rainfall in the transportation of suspended sediments from meltwater stream at a monthly scale. These in-situ based records on dynamics of suspended sediment and associated hydro-meteorological parameters are relevant for the planning and management of freshwater resources and planning for hydropower projects under a changing climate.

Quantification of volume loss and snout retreat from 1980 to 2019 of baspa basin glaciers, western himalaya

Himalayan glaciers are under the enhanced retreating process and filed observations are scarce due to the harsh terrain and inclement weather in the upper Himalayan region. Under these conditions, the use of remote sensing and GIS technique is the best option for long term change detection in glacial features. Glacier length, area, and volume change analyses have been done using Landsat data series (MSS, TM, ETM+, and OLI/TIRS) from 1980 to 2019. Glaciers of Baspa basin were digitized in 1980 and 75 glaciers were reported whereas in 2019, number of glaciers were 84. During the period of 1980 to 2019, the number of glaciers were increased by 9 in the Baspa basin but the volume has been reduced. The increase in number has been due to the conversion of larger glaciers into a few smaller glaciers under the melting process.The results showed a general trend of loss in the areas and volume of the glaciers with varying magnitudes at different glaciers of the Baspa basin and in different periods. The overall retreat during 1980–2019 has been 22.40 ± 4.46% with the average loss in the area as 1.11 ± 0.01 km2 a-1 in the entire Baspa basin. The smallest rate of loss in the glacier area has been observed as 1.05 ± 0.01 km2 a-1 from 2001 to 2013. The Baspa basin possessed a glacial volume of 16.26 km3 in the year 1980 that got reduced to 12.98 km3 by the year 2019. The total loss in 39 years (1980–2019) has been calculated as 3.28 km3. The rate of loss in volume is highest in the period 2013 to 2019 which is 0.116 km3 a-1 and the minimum rate of loss in volume was observed from 1994 to 2001 i.e. 0.035 km3 a-1.The results on changes in the areal cover of glaciers as well as the volume are important for quantification of future water availability on the basis which controls the water supply in the river system. It is also of use in the planning of the hydropower sectors as well as the existing power plants in terms of the potential to generate electricity.

UAV-Based Survey of Glaciers in Himalayas: Challenges and Recommendations

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 during UAV surveys on complex terrains of high mountain glaciers are inadequate and they are not available for places like Himalayas. Therefore, this study aims to examine and derive strategies to minimize those challenges on such complex glacier and their margin topography. Here, UAV surveys were conducted using a fixed-wing commercial-grade off-the-shelf UAV (eBee series, SenseFly) on three glacier sites (East Rathong, Hamtah and Panchinala-A) located in different climate regimes within the Indian part of Himalayas. From the UAV collected images, ultra-high-resolution ortho-mosaicked images and Digital Elevation Models were generated at 0.1 m ground sample distance and their accuracies were assessed using the collected ground control points. Based on the challenges observed, the study recommends criteria for selection of best-suited take-off/landing locations on a mountain glacier and its margins for conducting efficient UAV surveys in the complex terrain such as in the Himalayas and possibly beyond. Recommendations reported in this article shall be useful to minimize the challenges and associated risks during UAV data acquisition using fixed-wing UAVs.

Morphology and evolution of supraglacial hummocks on debris‐covered Himalayan glaciers

AbstractThick supraglacial debris layers often have an undulating, hummocky topography that influences the lateral transport of debris and meltwater and provides basins for supraglacial ponds. The role of ablation and other processes associated with supraglacial debris in giving rise to this hummocky topography is poorly understood. Characterizing hummocky topography is a first step towards understanding the feedbacks driving the evolution of debris‐covered glacier surfaces and their potential impacts on mass balance, hydrology and glacier dynamics. Here we undertake a geomorphological assessment of the hummocky topography on five debris‐covered glaciers in the Everest region of the central Himalaya. We characterize supraglacial hummocks through statistical analyses of their vertical relief and horizontal geometry. Our results establish supraglacial hummocks as a distinct landform. We find that a typical hummock has an elongation ratio of 1.1:1 in the direction of ice flow, length of 214 ± 109 m and width of 192 ± 88 m. Hummocky topography has a greater amplitude across‐glacier (15.4 ± 10.9 m) compared to along the glacier flow line (12.6 ± 8.3 m). Consequently, hummock slopes are steeper in the across‐glacier direction (8.7 ± 4.3°) than in the direction of ice flow (5.6 ± 4.0°). Longer, wider and higher‐amplitude hummocks are found on larger glaciers. We postulate that directional anisotropy in the hummock topography arises because, while the pattern of differential ablation driving topography evolution is moderated by processes including the gravitational redistribution of debris across the glacier surface, it also inherits an orientation preference from the distribution of englacial debris in the underlying ice. Our morphometric data inform future efforts to model these interactions, which should account for additional factors such as the genesis of supraglacial ponds and ice cliffs and their impact on differential ablation.

Effect Of Climate Change On Himalayan Regions

The climate change is one of the biggest challenges in the whole world. According to current situation the temperature of world can be anything between 1.5-5.80C.The warming rates of Himalaya is higher than rest of world. The rate of retreating of Himalayan glacier is six times greater than retreating rate of other glaciers of the world. The water supply the Asian countries like India, Bangladesh, Bhutan, China, Pakistan, Nepal, Afghanistan is done by the rivers which originate from Himalaya and the life circle, economic growth, agriculture and other requirement of life which is related to water of these countries is effected to the rivers which comes from Himalaya so it effected with any changes if happen in glaciers of Himalayas. The population of these countries is increases mainly of china and India at very fast rate, so in future their requirement in future will increase and the pressure on Himalayas will increase which is affected with continuing change climate change. Change climate has affected the Himalayas from various sides its glacier rate has accelerated, ecosystem and biodiversity has disturb in continuing pattern the flora and fauna is effected the species which were founded in low elevation regions in past decades is shifting towards upper elevation because of increase temperature this will create the problem of resources where they are shifting and competition is start for spacing we have no idea how long they will survive .Climate change also affected the alpine ecosystem this is most important by the point of view of medicine because 62%of medical plants are found from these parts. If this will continue affected then it will create great problem in the field of medicine. The increase temperature is favourable for female and transgender which is danger for their future production. The agricultural activity of above mention Asian countries is dependent on rivers which come from Himalaya due to retreating rate of glaciers of Himalayas there is chances of flood in future and due to change pattern of monsoon drought condition will come in future both drought and flood will create problems of live, diseases, food etc.

Role of sediment in solute acquisition in the Himalayan glacier meltwater stream, Gangotri glacier, Uttarakhand, India

AbstractLow temperature in‐stream solute acquisition in a glacial environment with very high suspended sediment is critical for downstream evolution of water chemistry. Present work is carried out on 18 km headwater reach from Gomukh (snout of the Gangotri glacier) to Gangotri along River Bhagirathi, India for understanding the hydrological processes controlling the solute acquisition in the glacial environment. This is the first attempt to conduct dissolution experiments with river bed sediments and meltwater considering different operating variables namely; contact time, seasonality, different sediment particle sizes, different sediment dose, effect of pH, wetting and crushing of bed sediments of the glacial stream. The role of sediment in low temperature solute acquisition process is characterized by sudden release of ions from the sediment in initial few seconds. Equilibrium time was observed to be 600 s (10 min). Further progressive increase in EC was observed from Gomukh to Gangotri, suggesting change in sediment surface characteristics/or source. Higher dissolution was observed from the bed sediments collected in June. It is found that the dissolution increases with increase in sediment doses but decreases with an increase in sediment particle size fraction. Higher solute acquisition was observed from crushed sediment because of an abundance of very fine particles having fresh, aggressive/reactive mineral surfaces which are capable of dissolution. The solute released from wetted sediment is significantly lower than the fresh sediment, which may be attributed to the destruction of microparticles adhering to mineral grains, the removal of fresh reactive surface sites, dissolution of rapidly weathered minerals such as calcite and evolution towards to equilibrium of the solution. Further, higher dissolution was observed with decrease in pH, which may be attributed to the availability of more hydrogen ion concentration of the solution, which favours more solute acquisition from sediment into meltwater.

Microbial Diversity in the Glacial Ecosystem of Antarctic, Arctic, and Tibetan Plateau: Properties and Response to the Environmental Condition

Microorganisms, as successive members of the food web, play a major role in biological processes. They are found in environments ranging from extremely hot to harsh cold temperatures. Thus, the study of bacterial communities in various ecosystems is of great concern around the world. The glacier is one of the parts of the cryosphere, which is the key component and sensitive indicator of climatic and environmental changes. A glacial ecosystem is a habitat for various microorganisms, i.e., autotrophic and heterotrophic. Different physicochemical parameters like temperature, pH, electrical conductivity, the input of nutrient concentration, precipitation, ions concentrations, etc. influence the microbial diversity in the glacial ecosystem for their metabolic processes. Successive studies of bacterial communities in the Himalayan glacial ecosystem are reliable proxies to know the relationships between microbial biodiversity and climate change since the Himalayan glaciers are free from anthropogenic activities. After the study of the relevant literature, it is clear that the researches. have been carried out in the Polar Regions, and the Tibetan plateau mainly focused on the glacial ecosystem. This review concluded that Proteobacteria, Bacteroidetes, Cyanobacteria, Firmicutes, Verrucomicrobia, and Actinobacteria were the most dominant bacterial phyla via 16S rRNA clone libraries and Illumina MiSeq. Alter in landscapes, nutrient cycles, exposure of light, shifting on the concentration of different elements, glacier retreats were the major components for survival strength of dominant bacterial phyla. However, limited studies on the glacial ecosystem of the Himalayas have been published. Thus, the study of bacterial abundance, diversity, and community in the Himalayas will help plug this research gap.

Source apportionment of the light absorbing impurities present in surface snow of the India Western Himalayan glaciers

Darkening of surface snow caused by deposition of the Light absorbing impurities (LAIs) can reduce its albedo and further enhance its melting. Early melting of surface snow leads to exposing the underneath ice mass to sunlight for longer duration and consequent retreat of glaciers. This retreat of glaciers, further cause several hydrological and climatic implications. In this study, efforts were made to perform source apportionment of the LAIs found in the surface snow samples, collected from the three glaciers located in the Indian Western Himalayas (IWHs). Ionic composition of the snow samples derived from ion chromatography was further analyzed using two receptor models viz., principal component analysis (PCA) and positive matrix factorization (PMF). It was observed that biomass burning, vehicular emissions, dust emissions and coal combustion were the major sources of the LAIs in the IWHs. The PMF analysis, estimated that biomass burning and vehicular emissions contributed ~30% each in the emission of the LAIs. Hybrid Single-Particle Lagrangian Integrated Trajectory (HYSPLIT)-based back trajectories for 7-days were plotted to identify locations of the sources of the LAIs. Back trajectories were observed to pass through agricultural, forest-covered and urban areas. The observations made, during this study, would help local authorities in identifying the hot spots of the LAIs’-emissions, on the basis of which region-specific policies could be framed to mitigate the anthropogenic emissions of the LAIs.

Impact of lockdown Covid-19 pandemic on himalayan environment

ABSTRACT The COVID-19 Pandemic have caused severe impact on lives in various ways, but our environment has experienced a positive outcome due to the lockdown which was imposed all over world including Himalayan region of India. The worldwide spread of COVID 19 has reduced movement of vehicles, industries and all tourism activities. Due to shutdown of all the commercial activities and traffic has helped the environment to reclaim naturally. The Himalayas is one of the world’s most fragile and sensitive hotspots to global climate change, with impacts manifesting at a particularly rapid rate. The Himalayan glaciers are the water towers of Asia, and the source of many of the world’s great rivers. In this research paper, an attempt has been made to describe the improvement in physiochemical characteristics of surface water, all parameters were compared with BIS standard of drinking water quality during pre lockdown and lockdown period. The ambient air quality have also been significantly improved and noise level were also found under permissible limit of Ambient air quality Standard.

Black carbon over a central Himalayan Glacier (Satopanth): Pathways and direct radiative impacts

Continuous measurement of Black Carbon (BC) concentration was carried out during May–October 2018 periods over Satopanth Glacier in the central Himalayas. BC concentrations varied between 28 and 287 ngm−3 on different days during the observational period. High concentration of BC was observed in the month of May (monthly mean of 221 ± 79 ngm−3), and a lower concentration was observed in August (monthly mean of 92 ± 58 ngm−3). Biomass burning was found to contribute up to 58% of BC mass over the region, with lower contribution during June and higher during the month of May. Compensation parameter (K) values were found to vary between −0.005 and 0.005 in different months, asserting the presence of aged BC in June to October months and relatively fresh BC in the month of May. Concentration weighted trajectory (CWT) analysis showed that the air mass from Indo Gangetic Plains (IGP) was responsible for the majority of transported BC in July & August months (up to 65%) and partially in September (up to 40%). However, the transport from Middle East and far north-western regions was found to be the major contributor to BC concentrations in other months. The estimated BC direct radiative forcing was found to induce 4.5 to 7.6 Wm−2 reduction of radiation at the surface (SFC) and the forcing was +2.3 to +3.5 Wm−2 at the Top of the Atmosphere (TOA). The BC induced atmospheric heating rates were found to be up to 0.35 k day−1 over the region. The sensitivity of snow albedo to radiative forcing was studied, and it is found that BC albedo changes tend to decrease albedo with an increase in BC-snow deposition, leading to a decrease in atmospheric absorption.

Climate Change, Water Scarcity, and the Potential for Interstate Conflict in South Asia

Ever since American security analysts began to consider the impact of global warming on international security, water has been viewed as an especially critical factor. In many parts of the developing world, water supplies are already insufficient to meet societal requirements, and, by shrinking these supplies further, climate change will cause widespread hardship, unrest, and conflict. But exactly what role water plays in this equation has been the subject of considerable reassessment over time. When analysts first examined warming’s impacts, they largely assumed that climate-related water scarcities would most likely provoke conflict within nations; only later did analysts look closely at the possibility of conflicts arising between states, typically in the context of shared river systems. This risk appears particularly acute in South Asia, where several highly-populated countries, including China, India, and Pakistan, rely on river systems which depend for part of their flow on meltwater from the Himalayan glaciers, which are contracting as a result of climate change. In the absence of greater efforts by these countries to address this peril in a collaborative, equitable manner, looming water shortages could combine with other antagonisms to trigger armed conflict, possibly entailing the use of nuclear weapons.

Glacier mass loss in the Alaknanda basin, Garhwal Himalaya on a decadal scale

The Himalayan glaciers significantly contribute to the largest river systems like the Indus, Ganga, and the Brahmaputra. The change in glacial area and mass can affect the mountain community and people living in the Indo-Gangetic plain. The present study adopted the geodetic method to estimate the elevation change and mass budget of 61 glaciers in the Alaknanda Basin, using the satellite data of Cartosat-1 (2011, 2014, 2017) and SRTM (2000). Besides, the DEM of 1962 (SOI Toposheet) and 2000 (SRTM) is used to estimate the mass budget of Satopanth (SPG) and Bhagirath Kharak glaciers (BKG). The field debris thickness of SPG (2015-2017) is compared with the elevation change (2000-2017). Further, we have compared the mass loss of the glaciers with their volume. The results suggest the sustained mass loss of 1.85 ± 0.10 Gt out of 33.9 ± 8.8 Gt for 61 glaciers in the basin from 2000-2017. The mass loss of SPG and BKG during 2000-2017 is 0.20 ± 0.02 Gt and 0.24 ± 0.03 Gt, whereas from 1962 to 2000, is 0.083 ± 0.03 Gt and 0.091 ± 0.04 Gt, respectively. The analysis facilitates a better understanding of glacier mass changes in the Alaknanda basin on a multi-decadal scale.

Voices from the Roof of the World

Glacier-based mountain water systems are the water towers of the world, and billions are dependent on the vital services they provide. In an effort to better understand the effects of climate change on the glaciers of the Hindu Kush-Himalaya, National Geographic and Tribhuvan University conducted a multidisciplinary expedition to Mount Everest. These are the voices from that journey.

Six Decades of Glacier Mass Changes around Mt. Everest Are Revealed by Historical and Contemporary Images

Summary The accurate quantification of current and past Himalayan glacier mass budgets is vital if we are to understand the evolution of the Asian water tower, which provides water to the planet’s most populous region. In this work, we generated a geodetic time series spanning six decades over 79 glaciers surrounding Mt. Everest and found consistent acceleration of glacier mass loss between the 1960s (−0.23 ± 0.12 mwe a−1) and the modern era (−0.38 ± 0.11 mwe a−1 from 2009 to 2018). Glacier mass loss has varied depending on glacier terminus type and surface characteristics, and glacier thinning is now occurring at extreme altitudes (>6,000 masl). Our time series also captures the first documented surge of a glacier in the Mt. Everest region. These multi-decadal observations of glacier mass loss form a baseline dataset against which physically based glacier evolution models could be calibrated before they are used for predicting future meltwater yield.

Exploration of Microbial Diversity of Himalayan Glacier Moraine Soil Using 16S Amplicon Sequencing and Phospholipid Fatty Acid Analysis Approaches.

Changme Khangpu glacier is located in the northern district of Sikkim which comes under UNESCO heritage site Kanchenjunga Biosphere Reserve which is considered as one of the important biological hotspot regions in the Eastern Himalayas. This is the first report on microbial diversity analysis of moraine soil from one of the unexplored glaciers of Sikkim using high throughput sequencing platform and phospholipid fatty acids analysis (PLFA). It was found that the 16S amplicon sequence comprised 362,902 raw sequences with a sequence length of 150bp and (G + C) content 52%. A total of 156,821 pre-processed reads were clustered into 378 OTUs (operational taxonomic units) comprising 6 bacterial phyla. The top four dominant phyla based on the 16S amplicon sequences were Proteobacteria (56%), Firmicutes (16%), Actinobacteria (12%), and Bacteroidetes (8%), respectively. PLFA analysis confirmed the dominance of Gram positive bacteria (72%) followed by Gram negative bacteria (32%) and the major fatty acids which are present in the moraine soil sample were PUFA (61%), and 18:2ω6,9c (29%). This is the primary study and first of its kind done on moraine soil from glaciers of Sikkim. Based on 16S amplicon sequencing and PLFA analysis of moraine soil samples from glaciers of Sikkim suggest that this glaciers harbours rich microbial diversity and thus can have wide industrial and biotechnological potential. Thus, there is an escalating scope to further study these extreme biomes with respect to their microbial diversity and their functional capabilities.

Sedimentological and mineralogical characteristics of active glacial sediments in the Indian Himalaya regions

ABSTRACT Glaciated sediments are a significant source to know the glacier environment processes. Glacial meltwater streams draining from the Himalayan glaciers carry with a different type of sediment sizes, because of the supraglacial, englacial, and subglacial debris, as well as formation of sediments from erosion by the movement of the ice. This study examines mineralogical and textural characteristics of sediments transported in the selected Indian Himalayan glacier meltwater streams. The results indicate that various sedimentological diversity occurring within proximity of active glaciations due to glacio-hydrological processes. Sedimentological and mineralogical characteristics suggest that sediments of the proglacial area are polygenic in nature. A comparative change in feldspar/quartz among bedrock, sand, and clay suggested that the active geochemical weathering regime at a low-temperature environment maturing the sand composition. The less clay fraction in glacier sediment indicates limited generation of clay minerals in the glacier environment. Change in clay composition from supraglacial moraine to proglacial environment indicated a chemical alteration in glaciated valley assisted by low slope glacio-fluvial environment.

Retreating Glacier and Advancing Forest Over the Past 200 Years in the Central Himalayas

AbstractThe Himalayan glaciers, as unique reservoirs of freshwater for densely populated Asian countries, have been receiving considerable attention in public and scientific research. However, little is known about their long‐term fluctuations as related to climate variability. Herein, we reconstructed glacier fluctuation events by tree ring‐based moraine dating and repeated photographs. We assessed these fluctuations over the past 200 years in the Gangapurna and Annapurna III glaciers, located in the central Himalayas. We detected five major glacier fluctuation events in the 1790s, 1920s, 1930s, 1960s, and 1970s. A higher rate of glacier recession was observed from the 1980s onward, coinciding with climate warming. As shown by repeated photographs, the retreating rate of the Gangapurna glacier from 1979 to 2016 (up to 24.4 m yr−1) is much higher than the Annapurna III glacier (7.54 m yr−1) from 1950 to 2016. Their different frontal retreat rates were likely related to microtopography and glacier sizes. Older moraines developed during and after the Little Ice Age (LIA) were already covered by dense forest, presenting the evidence for retreating glaciers and advancing forests in the central Himalayas. Ongoing warming tends to speed up such ecological processes by resetting biophysical environment of the deglaciated forefields. In general, glaciers have shown retreating trends over the last 200 years, presenting a risk for preserving water resources in the Himalayas and nearby regions. Alternatively, advancing forest tends to amplify warming rate by reducing albedo, which is a new issue for investigating ecohydrological feedbacks between mountain forests, climate, and water resources.

Volume-area scaling for debris-covered glaciers

AbstractA volume-area scaling relation is commonly used to estimate glacier volume or its future changes on a global scale. The presence of an insulating supraglacial debris cover alters the mass-balance profile of a glacier, potentially modifying the scaling relation. Here, the nature of scaling relations for extensively debris-covered glaciers is investigated. Theoretical arguments suggest that the volume-area scaling exponent for these glaciers is ~7% smaller than that for clean glaciers. This is consistent with the results from flowline-model simulations of idealised glaciers, and the available data from the Himalaya. The best-fit scale factor for debris-covered Himalayan glaciers is ~60% larger compared to that for the clean ones, implying a significantly larger stored ice volume in a debris-covered glacier compared to a clean one having the same area. These results may help improve scaling-based estimates of glacier volume and future glacier changes in regions where debris-covered glaciers are abundant.

GLACIAL LAKE EVOLUTION BASED ON REMOTE SENSING TIME SERIES: A CASE STUDY OF TSHO ROLPA IN NEPAL

Abstract. Himalayan glaciers have retreated rapidly in recent years. Resultant glacial lakes in the region pose potential catastrophic threats to downstream communities, especially under a changing climate. The potential for Glacial Lake Outburst Floods (GLOFs) has increased and studies have assessed the risks of those in Nepal and prioritised several glacial lakes for urgent and closer investigation. The risk posed by the Tsho Rolpa Glacial Lake is one of the most serious in Nepal. To investigate the feasibility of high-frequency monitoring of glacial lake evolution by remote sensing, this paper proposes a workflow for automated glacial lake boundary extraction and evolution using a time series of Sentinel optical imagery. The waterbody is segmented and vectorised using bimodal histograms from water indices. The vectorised lake boundary is validated against reference data extracted from rigorous contemporary unmanned aerial vehicle (UAV)-based photogrammetric survey. Lake boundaries were subsequently extracted at four different epochs to evaluate the evolution of the lake, especially at the glacier terminus. The final lake area was estimated at 1.61 km2, significantly larger than the areal extent last formally reported. A 0.99 m/day maximum, and a 0.45 m/day average, horizontal glacier retreat rates were estimated. The reported research has demonstrated the potential of remote sensing time series to monitor glacial lake evolution, which is particularly important for lakes in remote mountain regions that are otherwise difficult to access.