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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, considering rock and/or ice avalanches cascading into the lake. We consider ground surface temperature and topography to define avalanche source zones located in areas of potentially degrading permafrost. GLOF process chains in current and future scenarios, also considering engineered lake lowering of 10 and 30 m, were evaluated. Here, varied avalanche impact waves, erosion patterns, debris flow hydraulics, and GLOF impacts at Sissu village, under 18 different scenarios were assessed. Authors demonstrated that a larger future lake does not necessarily produce larger GLOF events in Sissu, depending, among other factors, on the location from where the triggering avalanche initiates and strikes the lake. For the largest scenarios, 10 m of lowering reduces the high‐intensity zone by 54% and 63% for the current and future scenarios, respectively, but has little effect on the medium‐intensity flood zone. Even with 30 m of lake lowering, the Sissu helipad falls in the high‐intensity zone under all moderate‐to‐large scenarios, with severe implications for evacuations and other emergency response actions. The approach can be extended to other glacial lakes to demonstrate the efficiency of lake lowering as an option for GLOF mitigation and enable a robust GLOF hazard and risk assessment. Plain Language Summary: Glacial lake outburst floods (GLOFs) have the potential to cause severe damage to the downstream regions. GLOFs can be triggered by a host of geomorphic, climatic, and seismic factors, one of which can be mass wasting such as avalanches entering a lake, particularly in the Himalaya where surrounding slopes are steep and destabilizing. In the Western Himalaya, Gepang Gath Lake has grown over the years to become the largest lake in Himachal Pradesh. The lake has potential to grow more than double its size in the future. The existence of warming permafrost (frozen ground) in the surrounding steep slopes of the lake makes it susceptible to failure. Assessment of GLOF process chains including avalanche impact on the lake, frontal dam breaching, and downstream impact shows that the nearest settlement at Sissu is exposed to present and future GLOFs. We further evaluated mitigation options, including lake level lowering by 10 and 30 m, to evaluate the changes in the GLOF intensities downstream of the lake. It is seen that there is a significant reduction in the GLOF impact downstream when the lake levels are lowered, but the risk from very large events is not eliminated. Key Points: Sissu is potentially exposed to high‐intensity glacial lake outburst flood hazard under all current scenarios and the moderate and large magnitude future scenariosLake lowering by 10 m reduces the high‐intensity zone by 54% and 63% for the current and future scenarios respectivelyLake lowering by 30 m leads to a reduction in the affected area of 78% and 93% in current and future scenarios, respectively [ABSTRACT FROM AUTHOR]

Indian Himalayas are home to numerous glacial lakes, which can pose serious threat to downstream communities and lead to catastrophic socioeconomic disasters in case of a glacial lake outburst flood (GLOF). This study first identified 329 glacial lakes of size greater than 0.05 km2 in the Indian Himalayas, and then a remote sensing‐based hazard and risk assessment was performed on these lakes. Different factors such as avalanche, rockfall, upstream GLOF, lake expansion, identification of the presence of ice cores, and assessment of the stability of moraine were considered for the hazard modeling. Further, a stochastic inundation model was applied to quantify the potential number of buildings, bridges, and hydropower systems that could be inundated by GLOF in each lake. Finally, the hazard parameters and downstream impact were collectively considered to determine the risk linked with each lake. A total of 23 lakes were identified as very high risk lakes and 50 as high‐risk lakes. The potential flood volumes associated with various triggering mechanisms were also measured and were used to identify the lakes with the most considerable risk, such as Shakho Cho and Khangchung Tso. This study is anticipated to support stakeholders and decision‐makers in identifying critical glacial lakes and make well‐informed decisions related to future modeling efforts, field studies, and risk mitigation measures. Key Points: Avalanche trajectories suggest that 36 out of 329 glacial lakes are susceptible to dynamic failure via an avalanche entering the lakeApplication of stochastic flood model reveals that 67 glacial lakes contain at least one hydropower system along their flow pathIndian Himalayas contain 23 critical glacial lakes, 17 of which are located in the state of Sikkim [ABSTRACT FROM AUTHOR]

Glacier retreat results in the formation and expansion, and sometimes outburst, of moraine-dammed lakes worldwide. Sudden outburst floods from such lakes have caused enormous damage to settlements and infrastructure located downstream. Such lakes located in the Himalayan region are highly prone to outburst floods due to climatic conditions and geotectonic settings. In this study, multi-temporal Landsat images from 2002-2014, digital elevation models (DEMs), geomorphic analysis and modelling were used to assess the changes in glacial lakes and the outburst susceptibility of moraine-dammed lakes in the Chandra-Bhaga basin of the north-western Indian Himalaya. An inventory of lakes was developed using satellite data, thematic maps and ground-based investigations for the Chandra-Bhaga basin. The total area of all glacial lakes (size >5000 m2) increased by 47% from 2002 to 2014, with a pronounced increase of 57% for moraine-dammed lakes. Sixteen moraine-dammed lakes were identified and assessed for outburst susceptibility using the analytic hierarchy process (AHP). Forty-one reported glacial lake outburst flood (GLOF) events from moraine-dammed lakes in Himalayan regions were analysed, culminating in the identification of 11 critical factors for assessing outburst susceptibility using the AHP, including those related to the lake area and change, surrounding terrain characteristics, dam geometry, regional seismicity and rainfall history. The past three GLOF events in the Himalayan region were used to validate the method and to classify moraine-dammed lakes as having very high, high, medium or low outburst susceptibility. Eight lakes classified as very high and high outburst susceptibility should be further investigated in detail. The proposed AHP-based approach is suitable for first-order identification of critical lakes for prioritising future detailed investigation and monitoring of moraine-dammed glacial lakes in the Himalayan region. Copyright © 2017 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

We present a new model called Bayesian Estimated Glacial Lake Volume (BE‐GLAV) to estimate the volume of proglacial lakes. Presuming the lake cross‐section as trapezoidal, BE‐GLAV uses a Bayesian calibration approach to adjust the cross‐sectional geometry to match modeled and observed lake surface widths. We validated our model using bathymetric measurements from lakes spread across High Mountain Asia (specifically, the Himalaya and Tien‐Shan), with aerial extents ranging from 0.01 to 5.5 km2. The modeled lake volumes agreed with the measured lake volume with a root‐mean‐square absolute uncertainty of ∼14%. With minimum and maximum errors of ∼0.3% and ∼61.2%, BE‐GLAV performed well compared to 10 other models in a model inter‐comparison experiment. Using the measured set of volumes, our model can constrain both the root mean square (RMS) error and the maximum percentage error in modeled lake volume, unlike other models, some of which can compute just the RMS uncertainty. Plain Language Summary: To estimate proglacial lake volume, we suggest a novel numerical model called BE‐GLAV, which is based on Bayesian calibration. The model minimizes the discrepancy between the measured and modeled lake surface width by assuming that the proglacial cross‐section is trapezoidal in shape. The model was applied to 66 lakes located in the Himalaya and Tien‐Shan. Modeled and measured volumes were in good agreement with each other (∼14% mean absolute uncertainty). We also compared our volume estimates to those predicted by 10 other models. These 10 models were scaling relationships between the area and volume of proglacial lakes. The comparison showed that, our model was among the top five performers, reducing the maximum error in lake volume by more than five times. BE‐GLAV is a good alternative to scaling models in areas where bathymetric surveys are scarce. When compared to scaling models, it is easy to implement and requires little calibration. Key Points: Bayesian calibration based estimation of proglacial lake volumeModel was validated over 66 lakes and the maximum error in modelled volume got reduced by >5 times as compared to scaling modelsRequires minimal calibration with observations as compared to scaling models [ABSTRACT FROM AUTHOR]

Estimating the frequency and magnitude of natural hazards largely hinges on stationary models, which do not account for changes in the climatological, hydrological, and geophysical baseline conditions. Using five diverse case studies encompassing various natural hazard types, we present advanced statistical and machine learning methods to analyze and model transient states from long‐term inventory data. A novel storminess metric reveals increasing European winter windstorm severity from 1950 to 2010. Non‐stationary extreme value models quantify trends, seasonal shifts, and regional differences in extreme precipitation for Germany between 1941 and 2021. Utilizing quantile sampling and empirical mode decomposition on 148 years of daily weather and discharge data in the European Alps, we assess the impacts of changing snow cover, precipitation, and anthropogenic river network modifications on river runoff. Moreover, a probabilistic framework estimates return periods of glacier lake outburst floods in the Himalayas, demonstrating large differences in 100‐year flood levels. Utilizing a Bayesian change point algorithm, we track the onset of increased seismicity in the southern central United States and find correlation with wastewater injections into deep wells. In conclusion, data science reveals transient states for very different natural hazard types, characterized by diverse forms of change, ranging from gradual trends to sudden change points and from altered seasonality to overall intensity variations. In synergy with the physical understanding of Earth science, we gain important new insights into the dynamics of the studied hazards and their possible mechanisms. Plain Language Summary: According to global databases on natural hazard events and associated risks, there has been a noteworthy escalation in the extent of economic losses during past decades. It is important but difficult to distinguish and disentangle trends due to changing hazard occurrence or damage potential. Accurately quantifying altered hazards requires high‐quality data sets and robust statistical methodologies. Here, we present recent progress in earth and data science toward a quantitative assessment of natural hazards in a changing world. We show that winter storms have become more frequent and more severe in Europe; that extreme precipitation in Germany shows seasonal shifts and changing intensities with regional variation; that river runoff in Central Europe is changing due to modifications of the river network, declining snowpacks, and changes in precipitation; that frequency of glacier lake outburst floods in the Himalayas have remained unchanged over the past 30 years despite rapid glacier melt and lake growth; and that earthquake activity in Oklahoma (USA) has increased with the onset of wastewater injection wells. We infer that recent advances in data science can efficiently provide new knowledge from big data sets, but interpreting these results needs a solid understanding and rather detailed analysis of the underlying processes. Key Points: Time‐dependent approaches are key to capture changing hazards, with diverse altered frequencies, intensities, timing or spatial occurrencesAdvances in data‐driven methods and increasing availability of geodata foster new ways to detect changes in natural hazardsOver‐simplification or averaging over large scales in time or space cause severe information loss and may hide the mechanisms for change [ABSTRACT FROM AUTHOR]

Cryospheric responses to climate warming include glacier retreat, altitude‐dependent thermal instability, and abundant meltwater, which increase the frequency of catastrophic glacier hazard chain (CGHC) events. Here we investigated the formation mechanism of a special CGHC event in 2018, in the Sedongpu Glacier, Eastern Himalayas, China. Based on the multi‐source remote sensing, seismic signal analysis, and numerical simulation, we conducted long‐term retrospective analysis and co‐event process reconstruction. The results show that the event could be divided into two phases. First, the hanging glacier with a volume of 8.5 × 106 m3 collapsed onto the downstream trunk glacier. Next, ∼1.17 × 108 m3 eroded materials from the impacted glacier transformed into debris flow and traveled downstream 8 km. During the cascading process, ice‐rock avalanche momentum and glacier velocity are key factors in determining CGHC formation and eventual volume. Our study helps better understand the domino effects of the CGHC disaster. Plain Language Summary: Glacier instability in cryosphere is significantly influenced by global warming. The glacial lake outburst floods are the most widely studied and catastrophic events resulting from this instability, but they are not the only ones. In recent years, increasing catastrophic glacier hazard chain (CGHC) events have reminded us of disasters during climate warming, especially in the Himalayas region. Here, we report a typical CGHC event in the Eastern Himalayas, where the retreated glaciers are widely distributed. Based on our observations and simulations, we completed the retrospective analysis of CGHC through its formation conditions, evolution process, and specific kinematic process. These analyses help us understand the driving mechanism, the volume‐increasing effect, and the super‐fluidity of CGHC. Our findings help improve such hazard chain identification and mitigation in the Eastern Himalayas and glacierized environments elsewhere in the world. Key Points: New insights of Ice‐rock avalanche hazard chain on retreated hanging glacier in Eastern HimalayaErosion process on the trunk glacier led to a volume‐increasing and super‐fluidity of catastrophic glacier hazard chain (CGHC)The pre‐evolution and formation of CGHC were closely related to climate warming [ABSTRACT FROM AUTHOR]

Infrequent, large‐magnitude discharge (>106 m3/s) outburst floods—megafloods—can play a major role in landscape evolution. Prehistoric glacial lake outburst megafloods transported and deposited large boulders (≥4 m), yet few studies consider their potential lasting impact on river processes and form. We use a numerical model, constrained by observed boulder size distributions, to investigate the fluvial response to boulder deposition by megaflooding in the Yarlung‐Siang River, eastern Himalaya. Results show that boulder deposition changes local channel steepness (ksn) up to ∼180% compared to simulations without boulder bars, introducing >100 meter‐scale knickpoints to the channel that can be sustained for >20 kyr. Simulations demonstrate that deposition of boulders in a single megaflood can have a greater influence on ksn than another common source of fluvial boulders: incision‐rate‐dependent delivery of boulders from hillslopes. Through widespread boulder deposition, megafloods leave a lasting legacy of channel disequilibrium that compounds over multiple floods and persists for millennia. Plain Language Summary: Megafloods (discharge equivalent to ≥400 instantaneously draining Olympic‐sized swimming pools per second) can transport a lot of material, including car‐ to house‐sized boulders. Because these boulders are so big, they remain in the channel until the next megaflood or until they weather into smaller pieces. We use a computer model to understand the impact of these megaflood deposited boulders on mountain river processes. We find that megaflood boulders can protect the river from being eroded, causing other processes, like tectonic uplift, to outcompete erosion. Megaflood boulders cause small steps to form within the river. Our modeling shows that these effects can be felt for >20,000 yrs after a single flood. We suggest that megaflood deposition (in addition to erosion) can cause a significant, unique change in mountain river processes. Key Points: We studied channel response to megaflood boulder deposition in the eastern Himalaya using a numerical modelMegaflood boulder deposition locally changes channel steepness up to 180%, creating >100 knickpointsThe compounding effect from multiple megaflood boulder deposits in rapid succession perturbs channel form for many thousands of years [ABSTRACT FROM AUTHOR]

Deglaciation has led to the transformation of glaciers into rock glaciers in various mountainous regions worldwide. However, the science of permafrost and rock glaciers remains under‐researched in the Himalayan region. This study presents a detailed inventory, dynamics, and permafrost distribution map for the Jhelum basin in the Kashmir Himalaya. The Permafrost Zonation Map (PZM) is created using a Logistic Regression Model based on topographic and climatic variables. High‐resolution satellite images are used to identify rock glaciers as visual indicators. Active and relic rock glaciers are classified based on surface topography and geomorphology. Results reveal 207 rock glaciers in the Jhelum basin, covering ∼50 km2, with over 100 falling into the active category. The PZM aligns well with the global permafrost zonation index map. Slope, aspect, and elevation of rock glaciers are computed using the ASTER Digital Elevation Model. The average elevations range from 3,700 m to 4,550 m, and the average surface slope ranges from 12° to 26°, with maximum slopes from 25° to 65°. Most rock glaciers are oriented toward the south or southeast. Field investigations confirm that these rock glaciers occur in highly elevated regions with steep slopes. This study provides valuable information on the high areal abundance of permafrost in the Himalayan region and suggests increased risks of thawing permafrost due to climate warming in the future. The findings contribute to the understanding of permafrost and rock glaciers, filling knowledge gaps in the Himalayan context. Plain Language Summary: In this study, we focused on understanding how glaciers turn into rock glaciers and how permafrost is distributed in the Jhelum basin of the Kashmir Himalaya. We found that many glaciers in mountainous regions around the world have transformed into rock glaciers due to deglaciation. However, there is limited research on permafrost and rock glaciers in the Himalayan region. Using satellite images and on‐the‐ground investigations, we created a detailed inventory and map of rock glaciers in the Jhelum basin. We also developed a permafrost distribution map by considering factors like temperature, solar radiation, and slope aspect. This map helps us understand where permafrost is located in the area. Our findings revealed that there are 207 rock glaciers in the Jhelum basin, covering an area of approximately 50 square kilometers. More than 100 of these rock glaciers are active. The map we created aligns well with existing global permafrost maps, showing the accuracy of our approach. This study enhances our knowledge of permafrost and rock glaciers in the Himalayan region, providing important information about their presence and the potential risks associated with thawing permafrost due to climate change. Key Points: Study investigates glacier‐to‐rock glacier transformation in Jhelum basin, Kashmir Himalaya due to deglaciationPresents detailed rock glacier inventory, dynamics, and permafrost distribution map using satellite images and field investigationsHighlights high permafrost abundance in Himalayan region, indicating increased thawing risks with climate warming [ABSTRACT FROM AUTHOR]

The high‐mountain system, a storehouse of major waterways that support important ecosystem services to about 1.5 billion people in the Himalaya, is facing unprecedented challenges due to climate change during the 21st century. Intensified floods, accelerating glacial retreat, rapid permafrost degradation, and prolonged droughts are altering the natural hydrological balances and generating unpredictable spatial and temporal distributions of water availability. Anthropogenic activities are adding further pressure onto Himalayan waterways. The fundamental question of waterway management in this region is therefore how this hydro‐meteorological transformation, caused by climate change and anthropogenic perturbations, can be tackled to find avenues for sustainability. This requires a framework that can diagnose threats at a range of spatial and temporal scales and provide recommendations for strong adaptive measures for sustainable future waterways. This focus paper assesses the current literature base to bring together our understanding of how recent climatic changes have threatened waterways in the Asian Himalayas, how society has been responding to rapidly changing waterway conditions, and what adaptive options are available for the region. The study finds that Himalayan waterways are crucial in protecting nature and society. The implementation of integrated waterways management measures, the rapid advancement of waterway infrastructure technologies, and the improved governance of waterways are more critical than ever. This article is categorized under:Engineering Water > Sustainable Engineering of Water [ABSTRACT FROM AUTHOR]

Himalaya is experiencing frequent catastrophic mass movement events such as avalanches and landslides, causing loss of human lives and infrastructure. Millions of people reside in critical zones potentially exposed to such catastrophes. Despite this, a comprehensive assessment of mass movement exposure is lacking at a regional scale. Here, we developed a novel method of determining mass movement trajectories and applied it to the Himalayan Mountain ranges for the first time to quantify the exposure of infrastructure, waterways, roadways, and population in six mountain ranges, including Hindu Kush, Karakoram, western Himalaya, eastern Himalaya, central Himalaya, and Hengduan Shan. Our results reveal that the exposure of buildings and roadways to mass movements is highest in Karakoram, whereas central Himalaya has the highest exposed waterways. The hotspots of exposed roadways are concentrated in Nepal, the North Indian states of Uttarakhand, Himachal Pradesh, the Union Territory of Ladakh, and China's Sichuan Province. Our analysis shows that the population in the central Himalaya is currently at the highest exposure to mass movement impacts. Projected future populations based on Shared Socio‐economic and Representative Concentration Pathways suggest that changing settlement patterns and emission scenarios will significantly influence the potential impact of these events on the human population. Assessment of anticipated secondary hazards (glacial lake outburst floods) shows an increase in probable headward impacts of mass movements on glacial lakes in the future. Our findings will support researchers, policymakers, stakeholders, and local governments in identifying critical areas that require detailed investigation for risk reduction and mitigation. Plain Language Summary: Avalanches and landslides are common in mountainous terrain like the Himalaya. Failure of the steep slopes can threaten infrastructure and population in the downstream regions. Also, such failures in glaciated terrain can potentially impact high‐altitude lakes, thereby leading to downstream flooding. The assessment carried out in this study covering the mountain ranges in the Hindukush Karakoram Himalaya identifies the exposed elements, including buildings, roadways, waterways, population, and glacial lakes to potential mass movements. Further, downstream impact from glacial lake outburst depends on the location of the lake with respect to the mass movement impact direction, that is, striking direction. Our findings show that the exposure depends on the mass movement magnitude and is concentrated in the eastern and central Himalayas, where population and lake densities are high. Also, exposure of buildings and roadways to mass movements is highest in Karakoram. Future population exposure to slope failures shows significant changes based on the varied socio‐economic conditions. Key Points: First‐order assessment shows that central Himalaya has the highest exposed waterways to potential mass movementsCentral Himalaya is identified as the hotspot with the highest exposed population to mass movements in the present as well as in the futureHeadward impacts on glacial lakes are highest in Eastern Himalaya, which shifts to the Karakoram and Western Himalaya in the future [ABSTRACT FROM AUTHOR]

Permafrost degradation increases the likelihood of glacial lake outburst floods on the Tibetan Plateau. Analyses of the freeze–thaw conditions in moraine dams and associated impacts on dam stability contribute toward reducing natural hazard risks. We used the heat transfer module of COMSOL Multiphysics to simulate the soil temperature field in the Longbasaba moraine dam, which is on the northern slope of central Himalaya. There is close agreement between the simulated and observed soil temperature values. Root mean squared errors (the square root of the mean of the square of all of the error) are below 1.30°C and mean bias errors vary from −0.10 to −0.52°C for the different soil layers. Between 1959 and 2020, active layer thickness increased at a mean annual rate of 0.024 m a−1. Under the Coupled Model Intercomparison Project Phase 6 scenarios, the buried ice inside the moraine dam is clearly melting. The maximum‐buried ice thaw depth is currently 3.4 m and at the end of the 21st century is projected to be 9.53, 16.69, and 21.83 m under SSP1‐2.6, SSP2‐4.5, and SSP5‐8.5, which indicates a continuous decrease in moraine dam stability. Plain Language Summary: Glacial Lake Outburst Floods have frequently occurred on the Tibetan Plateau in recent years and have caused many casualties and substantial property damage. Longbasaba lake is located at the end of Longbasaba glacier and is dammed by a terminal moraine complex. We used the heat transfer module of COMSOL Multiphysics simulation software to simulate the freeze–thaw process and melting of buried ice inside the Longbasaba moraine dam between 1959 and 2100 and examined dam stability. The maximum thawing depth of the dam in summer has increased over the past decades and buried ice has been melting since the mid‐1970s. Under future warming scenarios, the depth of melting inside the dam is projected to exceed the depth of freezing and the melting rate of buried ice will accelerate. This indicates that seepage and piping will increase and dam stability will continue to decrease. We must remain alert about the possibility of future dam failure. Key Points: Soil temperatures at different depths of the Longbasaba moraine dam were well simulated by COMSOL Multiphysics softwareBetween 1959 and 2020, annual active layer depth increased at a mean rate of 0.024 m a−1Under Coupled Model Intercomparison Project Phase 6 scenarios, melting of buried ice is projected to accelerate and reduce dam stability [ABSTRACT FROM AUTHOR]

The west‐central Himalayan River basins face significant damage caused by extreme floods annually. We selected the upper Ganga basin (UGB), the west‐central Himalayan basin, to demonstrate how maximum cumulative storm and total rainfall received during monsoon control the extreme flow variability. In addition, the downscaled CMIP6 data sets were used for projections of extremes. The results suggest that historically Alaknanda basin receives a relatively higher magnitude of monsoon and storm rainfall than the other regions in the UGB, which manifested into significant extreme flow variability at the Alaknanda outlet. The extreme flows at the UGB outlet are projected to be more frequent under warming scenarios. The nonstationary flood frequency magnitudes are higher than those obtained from the stationary frequency method, implying a need for a review of return periods used in the designs of flood control structures in the region. Plain Language Summary: Floods are frequent natural disasters in India that affect millions of people and disrupt socioeconomic conditions. Climate change and human interventions further exaggerate flood hazards in many regions of the country. The west and west‐central Indian Himalayas are the worst flood‐affected regions in recent decades. A detailed scientific analysis is, therefore, crucial for sustainable flood management. Here, we analyze the historical behavior and future projections of annual maximum flows in the upper Ganga basin (UGB; located in the west‐central Himalayan region). Our results indicate that the eastern Alaknanda basin has historically been a highly flood‐prone region in the UGB. The warming climate might further amplify the extreme flood hazards. The nonstationary flood magnitudes are also expected to intensify, posing a severe threat to the operation of hydraulic structures. These inferences would be helpful in formulating sustainable flood mitigation strategies for the west‐central Himalayan region. Key Points: Eastern Alaknanda basin is one of the worst flood‐affected regions in the upper Ganga basinWarming climates are observed to amplify the extreme flood magnitudes in the upper Ganga basinNonstationary flood frequency magnitudes are higher than those obtained from the stationary frequency method [ABSTRACT FROM AUTHOR]

The dynamic response of large mountain glaciers to climatic forcing operates over timescales of several centuries and therefore understanding how these glaciers change requires observations of their behavior through the Holocene. We used Be‐10 exposure‐age dating and geomorphological mapping to constrain the evolution of glaciers in the Khumbu Valley in the Everest region of Nepal. Khumbu and Lobuche Glaciers are surrounded by high‐relief lateral and terminal moraines from which seven glacial stages were identified and dated to 7.4 ± 0.2, 5.0 ± 0.3, 3.9 ± 0.1, 2.8 ± 0.2, 1.3 ± 0.1, 0.9 ± 0.02, and 0.6 ± 0.16 ka. These stages correlate to each of the seven latest Holocene regional glacial stages identified across the monsoon‐influenced Himalaya, demonstrating that a coherent record of high elevation terrestrial palaeoclimate change can be extracted from dynamic mountain landscapes. The time‐constrained moraine complex represents a catchment‐wide denudation rate of 0.8–1.4 mm a−1 over the last 8 kyr. The geometry of the ablation area of Khumbu Glacier changed around 4 ka from a broad, shallow ice tongue to become narrower and thicker as restricted by the topographic barrier of the terminal moraine complex. Plain Language Summary: Satellite observations indicate that glaciers in the monsoon‐influenced Himalaya are changing rapidly in response to climate change. However, understanding why glaciers are changing requires observing glacier behavior over longer timescales using the glacial geological record. We mapped the geometry and measured the ages of ice‐marginal moraines built by two adjacent glaciers in the Everest region of Nepal. The moraines represent a complete record of glacier expansion during cold periods in the monsoon‐influenced Himalayan region over the last 8,000 years. Moraines formed by the large Khumbu Glacier and the smaller, steeper Lobuche Glacier also reveal differences in how these glaciers have changed since the last Ice Age. The results are useful to understand how monsoon‐influenced Himalayan glaciers respond to climate change, and to improve projections of their future behavior. Key Points: Ice‐marginal moraines in the upper Khumbu Valley represent a complete record of regional glacier change between 7.4 ka and the present dayMoraine building modified the response of Khumbu Glacier to climate change after 8 kaHolocene moraine volume indicates a catchment‐wide denudation rate of 0.8–1.4 mm per year [ABSTRACT FROM AUTHOR]

Profound effects of episodic megafloods (≥106 m3/s) have been observed on Earth and Mars. Quaternary megafloods sourced from valley‐blocking glaciers on the Tibetan Plateau likely play an important role in the geomorphic evolution of the Yarlung‐Tsangpo Gorge and mountain landscape of the eastern Himalaya. We use the first 2D numerical simulation of a megaflood sourced from a reconstructed 81 km3 Tibetan lake to analyze flood hydraulics and examine the erosional and depositional potential of megafloods in mountain landscapes. The simulated flood has a duration >60 hr and a peak discharge of 3.1 × 106 m3/s. We find that the extent of inundated features like terraces, narrow valley sections, tight meander bends, and overtopped ridges influences locations of observed maximum depth (370 m), speed (76 m/s), and bed shear stress (>100 kPa), creating dynamic patterns of erosive potential. Consequently, it is difficult to predict local (≤1 km) patterns of megaflood erosional potential from either unit stream power or flood power from smaller magnitude outburst floods. However, both are useful when predicting regional (≥25 km) order‐of‐magnitude shifts in megaflood flood power. Portions of the flood domain downstream of the Gorge experience lower bed shear stresses and flood power <5 kW/m2, indicating potential for significant deposition. We suggest widespread deposition of boulders within the modern channel and fine‐grained particles on hillslopes during a megaflood likely impedes subsequent erosion and affects channel width and longitudinal form throughout the flood pathway. Our findings show the legacy of megaflooding in mountainous terrain includes both extensive erosion and deposition. Plain Language Summary: Megafloods are catastrophic floods with a fast‐moving peak discharge of at least a million cubic meters (the volume of around 400 Olympic‐sized swimming pools) per second that are usually sourced from the sudden drainage of lakes formed behind unstable landslide or glacier dams. While previous scientists have studied the flow of megafloods in other, lower relief parts of the world, little is known about how these immense floods behave in steep mountainous landscapes. We simulated a megaflood in the eastern Himalaya and found that the simulated flood had a peak discharge of 3.1 million m3/s—three times higher than predicted from simple estimates using lake volume and dam height. We find that the hydraulics of this megaflood are directly related to the shape of the river valley (i.e., whether or not the water flowed over ridges and/or terraces or whether the river path took a sharp turn) and they change continuously throughout the flood. This means the patterns of removed material after a megaflood will be directly related to shape of the flooded landscape. Additionally, we predict that megafloods leave behind a lot of sand and large boulders—deposition that might impact where the modern river can erode. Key Points: 2D hydraulic simulation of a Holocene megaflood in the eastern Himalaya produces peak discharge of 3.1 × 106 m3/s and bed shear stress >100 kPaLocal megaflood erosion will reflect interactions between valley topography and flood hydraulics more than patterns of unit stream powerMegaflood boulder/sand deposits could impede later erosion by smaller flows with potential long‐term impacts on mountain landscape evolution [ABSTRACT FROM AUTHOR]

Heavy snowfall and gale-force winds associated with these WDs can lead to snow avalanches. The highest snowfall in this month occurred on 14 January, when Kupwara received 70cm of snowfall, Gulmarg 67.8cm and Pahalgam 54.3cm. By then, the accumulated snowfall was above 250cm in many places (Figure 6) and it remained for many weeks afterwards. GLO:65TF/01oct21:wea3938-fig-0001.jpg PHOTO (COLOR): 1 Snowfall pictures from different locations during 2019/2020 winter season. gl All that is required for an avalanche to occur is a mass of snow and a steep enough slope for it to slide down. An avalanche is triggered when a cohesive slab of snow lying upon a weaker layer of snow fractures and slides down a steep slope (McClung and Schaerer, 1993). [Extracted from the article]

Globally, urban wetlands are facing immense pressure from land use land cover changes (LULCCs) and associated water quality degradation that is severely affecting the trophic status of these ecosystems. This study analyzed water quality degradation resulting from land system changes in the vicinity of Khushalsar, an urban Wetland, in Srinagar City from 1980 to 2017. The analysis of satellite data indicated that this Wetland lost ~18.1 ha from 1980 to 2017. During the same period, the urban area within the Wetland increased from 0.2% to 16.5%. The land cover changes assessed in the vicinity of Wetland indicated an increase of 119% and 62.8% in built‐up and roads respectively. The analysis of surface water quality of the Wetland showed widespread degradation. The Trophic state index ranged from 73.4 to 84.6 indicating hyper‐eutrophic waters. A snapshot of comparative water quality data from 2002 to 2018 revealed that the mean concentration of NO3−‐N increased from 219 to 433 μg L−1 and that of total phosphorus increased from 135.4 to 1,236 μg L−1 indicative of continuous nutrient enrichment. Hierarchical cluster analysis (HCA) grouped eight sampling sites into four clusters based on likeliness of water quality characteristics. Similarly, discriminant analysis showed the formation of similar patterns of clusters, corroborating the HCA. Principal component analysis suggested three principal components accounting for a cumulative variance of 90.61%. The unplanned land system changes vis‐a‐vis human‐induced water quality degradation together with the lack of a monitoring mechanism have brought the Khushalsar Wetland to its current hyper‐eutrophic state. [ABSTRACT FROM AUTHOR]

Thick 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. [ABSTRACT FROM AUTHOR]

This study explores paleoflood deposits of the Siang River, known as the Tsangpo in Tibet. The river that often experiences large floods brings down huge amount of sediment and water that adversely affect the downstream regions with large human populations in the states of northeast Himalaya and its foreland. Along it's ~300 km mountainous stretch we collected samples for sedimentological, petrographic and Sr–Nd isotopic study to explore sediment provenance and dated the paleofloods (via optically stimulated luminescence, OSL). Geomorphic indices including precipitation and a geomorphic swath profile across the Brahmaputra catchment were studied to understand the interplay of mountain relief and rainfall that determine potential zones of high erosion and sediment supply. The OSL technique indicated the Siang River experienced at least eight large floods between 7 and 1 ka, possibly under the influence of warm and wet climatic conditions. The petrographic and isotopic data suggests that the eastern Himalayan syntaxis, which has the highest uplift and exhumation rate in the area, is not always the highest sediment producing zone. In some instances, the Tibetan plateau produces higher fluxes of sediments via glacial and landslide lake outburst floods (GLOFs and LLOFs). © 2020 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

The mountain systems of the Hindu Kush Himalaya (HKH) are changing rapidly due to climatic change, but an overlooked component is the subnival ecosystem (between the treeline and snow line), characterized by short‐stature plants and seasonal snow. Basic information about subnival vegetation distribution and rates of ecosystem change are not known, yet such information is needed to understand relationships between subnival ecology and water/carbon cycles. We show that HKH subnival ecosystems cover five to 15 times the area of permanent glaciers and snow, highlighting their eco‐hydrological importance. Using satellite data from the Landsat 5, 7 and 8 missions, we measured change in the spatial extent of subnival vegetation from 1993 to 2018. The Landsat surface reflectance‐derived Normalized Difference Vegetation Index product was thresholded at 0.1 to indicate the presence/absence of vegetation. Using this product, the strength and direction of time‐series trends in the green pixel fraction were measured within three regions of interest. We controlled for cloud cover, snow cover and evaluated the impact of sensor radiometric differences between Landsat 7 and Landsat 8. Using Google Earth Engine to expedite data processing tasks, we show that there has been a weakly positive increase in the extent of subnival vegetation since 1993. Strongest and most significant trends were found in the height region of 5,000–5,500 m a.s.l. across the HKH extent: R2 =.302, Kendall's τ = 0.424, p <.05, but this varied regionally, with height, and according to the sensors included in the time series. Positive trends at lower elevations occurred on steeper slopes whilst at higher elevations, flatter areas exhibited stronger trends. We validated our findings using online photographs. Subnival ecological changes have likely impacted HKH carbon and water cycles with impacts on millions of people living downstream, but the strength and direction of impacts of vegetation expansion remain unknown. [ABSTRACT FROM AUTHOR]

A landslide occurred in the region of Zanskar in the Indian Himalayas in 2015, damming the Tsarap River, creating a lake that effectively became a ticking time bomb, threatening villagers downstream. During the period between the discovery of the natural dam and the bursting of the lake, the state's approach to disaster management plunged the local population into a situation where 'technocratic time' ruled, as government experts handled the impending disaster at a rhythm dictated by the production of studies and reports. Analysis of the temporality of disaster mitigation and preparedness measures during this anticipated flood, as well as of the factors that surrounded the events, reveals how attitudes towards the state shaped people's perceptions of these interventions. In Zanskar, the technocratic pace and the state's lack of transparency were seen as a form of oppression that further marginalised the region, in particular by subjecting its population to the process of waiting. [ABSTRACT FROM AUTHOR]

Glacial lake outburst floods are among the most serious natural hazards in the Himalayas. Such floods are of high scientific and political importance because they exert trans-boundary impacts on bordering countries. The preparation of an updated inventory of glacial lakes and the analysis of their evolution are an important first step in assessment of hazards from glacial lake outbursts. Here, we report the spatiotemporal developments of the glacial lakes in the Poiqu River basin, a trans-boundary basin in the Central Himalayas, from 1976 to 2010 based on multi-temporal Landsat images. Studied glacial lakes are classified as glacier-fed lakes and non-glacier-fed lakes according to their hydrologic connection to glacial watersheds. A total of 119 glacial lakes larger than 0.01 km2 with an overall surface area of 20.22 km2 (±10.8%) were mapped in 2010, with glacier-fed lakes being predominant in both number (69, 58.0%) and area (16.22 km2, 80.2%). We found that lakes connected to glacial watersheds (glacier-fed lakes) significantly expanded (122.1%) from 1976 to 2010, whereas lakes not connected to glacial watersheds (non-glacier-fed lakes) remained stable (+2.8%) during the same period. This contrast can be attributed to the impact of glaciers. Retreating glaciers not only supply meltwater to lakes but also leave space for them to expand. Compared with other regions of the Hindu Kush Himalayas (HKH), the lake area per glacier area in the Poiqu River basin was the highest. This observation might be attributed to the different climate regimes and glacier status along the HKH. The results presented in this study confirm the significant role of glacier retreat on the evolution of glacial lakes. Copyright © 2014 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]