We welcome contributions investigating in space and time:
- catastrophic mobilization of sediments and cascading events
- hazards associated with deposition and runout features
- concepts of compounding and cascading dynamics
- connectivity between hillslopes and river networks
- feedback loops of stabilizing and destabilizing processes on the slopes
We invite presentations that focus on observational, conceptual, methodological, or modeling approaches or a combination of those in all kinds of mountain environments and particularly encourage early career scientists to apply for this session.
On October 3, 2023, a glacial lake outburst flood (GLOF) occurred at South Lhonak Lake in Northern Sikkim, India, resulting in extensive downstream destruction with transboundary effects extending hundreds of kilometers. The GLOF was triggered by the failure of the lake's perennially frozen and rapidly creeping North lateral moraine, leading to a displacement wave that overtopped and breached the frontal moraine dam. The resulting flood wave severely impacted the downstream valley, claiming lives and damaging infrastructure, including numerous buildings, bridges, roads, and hydropower plants. It completely destroyed the Teesta III hydropower project, at Chungthang located 63 km downstream of the lake. In our study, we employ a multi-model approach to reconstruct the GLOF process chain and analyze its associated geomorphic processes. We utilized various proxies, including flood marks, changes in lake volume before and after the GLOF, and flow velocity measurements to calibrate our models. Our calculations indicate that the erosion and deposition volumes from this event classify it among the most devastating GLOFs recorded to date. Additionally, we identify landslides triggered by the GLOF and assess their impacts on local infrastructure. Our study underscores the urgent need for improved monitoring and risk management strategies in mountain regions exposed to such extreme cascading events.
How to cite: Sattar, A. and the SLL GLOF investigating team: The South Lhonak GLOF Cascade of October 2023, Sikkim Himalaya, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-768, https://doi.org/10.5194/egusphere-egu25-768, 2025.
The history of Himalayan hydropower is dotted with severe accidents due to high-mountain hazards such as earthquakes, glacial lake outburst floods, and mass movements. Regardless, India is set to expand the development of large hydroelectric power projects, in particular in its Himalayan states. In Nepal, 85 new projects are currently under construction, and an additional 82 projects are under consideration. China approved plans to build the world’s largest hydropower dam along the Yarlung Zangbo River, and accelerated construction of hydropower dams along Tibet’s major rivers.
Clean, flexible, reliable and renewable energy is needed to satisfy increasing power demands, meet sustainability goals, and advance towards a carbon-free future. However, intensification of precipitation events, glacier retreat, and permafrost decay in the wake of global warming do not bode well for the future of high-mountain hydropower endeavors. For this reason, research is needed that offers quantitative assessments of hazards to hydropower and associated risks.
In this talk, I will showcase recent natural extreme events and their impact on Himalayan hydropower, and I will detail how regional assessments can help identifying river reaches that are exposed to natural hazards. While these assessments explicitly and quantitatively acknowledge uncertainties to guide disaster prevention, recent extreme events and their cascading nature underscore limits to hazard and risk assessments. These challenges to predict the diversity of rare and destructive events in the Himalayan environment need to be addressed to ultimately warrant that hydropower generation remains a sustainable undertaking.
How to cite: Schwanghart, W.: Natural hazards and the sustainability of Himalayan hydropower, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-20363, https://doi.org/10.5194/egusphere-egu25-20363, 2025.
Glacial lake outburst floods (GLOFs) are recognized as a major hazard in many mountainous regions of the world, and particularly in the Himalaya. Much of the efforts around GLOF mitigation and early warning in the Himalaya focuses on lakes classified as dangerous, which are generally large; however, even small glacial lakes can produce devastating floods. This was illustrated on 16 August 2024, when a glacial lake outburst flood struck the village of Thame, in the Khumbu region of Nepal. The GLOF originated from a cascade of two small lakes that had not previously been considered dangerous. We use a combination of seismic, remote sensing, meteorologic and gauge data, and field observations to examine the GLOF dynamics, impacts, and potential triggers. The combination of all the data suggests that a wet snow avalanche into the upper bedrock dammed lake was the most likely trigger of the GLOF. The resulting impulse wave overtopped the upper lake, sending a flow 650 m downstream to the lower lake, leading to a breach of the lower lake’s moraine dam. Overall, we estimate that ~4-5 x 105 m3 of water was released from the two lakes. Before and after Pleiades and HMA DEMs reveal a complex pattern of erosion and deposition as the GLOF propagated down the Thame Khola valley. In the village of Thame, damage resulted from inundation, coarse sediment impacts, and erosion of a paleochannel passing through the village. Despite the small initial volume of the GLOF, impacts continued far downstream on the Dudh Koshi, including landslide damage to a key road bridge ~45 km downstream of the GLOF source. This GLOF highlights both the risk of small glacial lakes and the need to understand GLOF erosion and deposition dynamics in order to properly estimate hazard.
How to cite: Cook, K. L., Shrestha, D., Brun, F., Berthier, E., and Charrier, L.: The 2024 Thame GLOF, Khumbu Nepal - causes, consequences, and dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12752, https://doi.org/10.5194/egusphere-egu25-12752, 2025.
Complex cascading processes such as glacial lake outburst floods (GLOFs), or rock slides or rock-ice avalanches evolving into long-runout debris flows or related phenomena, are fairly common phenomena in glacierized high-mountain areas. Massive events resulting in severe losses have triggered scientific and public attention in the early 2020s, such as the Chamoli process chain in 2021 and the South Lhonak process chain in 2023. Managing the related risks is a complex and challenging task. Social scientists emphasize the need for better strategies of policy implementation and increasing awareness and preparedness, whereas researchers with a background in natural and technical sciences often believe in the importance of computer models to predict or to better understand process chains.
This contribution summarizes the current efforts, trends, and challenges in the simulation of cascading hydrogeomorphic processes in high-mountain areas. The past decade has seen major progress in model development and application, with emerging tools allowing to move from model chains to integrated multi-phase approaches. At the same time, major challenges in terms of process understanding and uncertainties of data and parameters have been identified. “Successful” back-calculation of events is often based on case-specific parameter optimization, whereas predictive modelling efforts, despite some progress, face a number of conceptual and practical challenges. A still emerging field consists in the use of model results for science communication and awareness- and preparedness-raising – employing, for example, virtual reality, augmented reality, and computer gaming. Such efforts may help bridging the gap to the societal components of risk management.
How to cite: Mergili, M.: Hydrogeomorphic process chains in high-mountain areas: a modelling perspective, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10287, https://doi.org/10.5194/egusphere-egu25-10287, 2025.
High mountain expeditions in the Nepal Himalayas occur in a region particularly prone to natural hazards, fueled by the accelerating impacts of ongoing climate change. These hazards, such as avalanches, rockfalls and serac falls, are amplified by rising temperatures and glacier melt. Despite growing awareness, a systematic exploration of the interplay between climate change, natural hazards, and the high-altitude mountaineering, which plays a dominant economic role for Nepal remains absent.
Our study addresses this gap by analyzing how climate change, natural hazards, and expedition success and/or mortality rates relate. Leveraging a comprehensive dataset (The Himalayan Database, spanning 1905–2019), state-of-the-art meteorological reanalysis data (ERA5-Land), we developed Bayesian hierarchical multilevel models to quantify temporal trends in success and/or mortality and how they relate to trends in natural hazard occurrence. We selected 29 peaks above 7,000 m with over 20 expedition entries resulting in an expedition catalogue containing 7,747 expedition entries. We focused on impacts of extreme conditions, storms, avalanches, and seracs. A text-mining approach classified climbing routes and identified hazard occurrences based on expedition logs.
Our first findings reveal notable trends. First, summit bid time windows, i.e. the time between leaving the basecamp and reaching the summit, has consistently decreased over time, potentially reflecting a shortening of optimal and stable climbing conditions which we demonstrate to deteriorate as a function of climate change. Alternatively, shortened summit bid time windows may be indicative of increasing efficiency of touristic mountain expeditions. Second, the reported incidence of storms and avalanches has declined relative to the total number of expeditions, while the mortality rate associated with these hazards, however, has increased, with avalanche-related fatalities rising from 0.150 to 0.195. Likewise, storm-related mortality also slightly increased from 0.010 to 0.014. This finding suggests that expeditions are likely better prepared for summit bids, e.g. improved weather forecasts, yet that the magnitude of deadly incidents may have increased over time. Third, our analysis of climate and weather data reveals that mountaineering expeditions in the Himalayan region are increasingly subject to extreme weather events and hazardous compound events such as snowstorms.
Our findings underscore the need for enhanced safety measures and a deeper understanding of climate-hazard dynamics to mitigate risks to mountaineers. This study may help advancing our knowledge of how global warming alters the risk portfolio high mountain explorers are exposed to, eventually providing valuable insights for stakeholders in mountaineering and tourism.
How to cite: Kusch, E. and Mohr, C. H.: High Hopes and Broken Dreams – The interplay of climate change, natural hazards, and the mortality of high mountain expeditions in the Nepal Himalayas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-10656, https://doi.org/10.5194/egusphere-egu25-10656, 2025.
Cascading sediment flows in extratropical mountain ranges could be enhanced by an increasing frequency of warmer storms over the next century. We present analysis of the geomorphological and sedimentological impact of two rain-induced catastrophic sediment transport events that occurred just 54 days apart on the Rio Teno, Central Chilean Andes. Despite the second storm generating 50-80% smaller peak flood magnitudes and 1.3 times fewer mass movements, we find evidence for the catastrophic reworking of riverbed sediments that scale in magnitude with the first event. We argue that beyond the individual disruptive event, warm storms have the potential to prime mountain river systems for subsequent sediment transport events during smaller floods. To forecast the evolution of sediment fluxes from mountain ranges over the next century, we therefore need to go beyond assuming a simple relationship between sediment export and the frequency of sediment mobilising flood events to consider the disproportional response of the sediment system to smaller floods following more frequent warm storms.
How to cite: Harries, R., Vergara, I., Serey, A., Villaseñor, T., Orr, E., Aguilar, G., Vergara, P., and Marquardt, C.: Catastrophic sediment transport preconditioned by warm storms, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18435, https://doi.org/10.5194/egusphere-egu25-18435, 2025.
Single-grain post-infrared luminescence (SG-pIRIR) is able to trace river sediment dynamics stored in fluvial deposits through the interpretation of scatter in equivalent dose (De) distribution caused by heterogeneous bleaching (zeroing) of grains by sunlight exposure prior to deposition. Despite the challenge of heterogeneous bleaching, studies have observed that, in such settings though, luminescence signals measured in modern deposits tend to be better bleached downstream. It thus suggests that the study of alongstream luminescence signals may allow the quantification of fluvial transport processes and the transient storage of particles in floodplains.
This study explores SG-pIRIR De distribution from feldspars in modern floodplain deposits of the Río Ñuble (Chile) before and after a major rainfall and discharge event, to investigate whether SG-pIRIR luminescence can be used to trace the impact of such an extreme hydrological event on landscape erosion. This event took place in austral winter 2023, with cumulative rain exceeding 700 mm over 72 hours in the foothill regions, causing large-scale flooding of Andean rivers including adjacent lowlands. The comparison of SG-pIRIR De distribution before and after the event reveals a systematic increase in SG-pIRIR De values, with post-flood data exhibiting a pronounced increase in SG-pIRIR De, enhanced by a factor of 200–300 compared to the pre-flood data. Moreover, the increase of De values varies longitudinally being most pronounced at the front of the Andean Cordillera. We show that this pattern likely reflects the influx of newly eroded material in areas of the most intense rainfall and thus discharge during the flood. It indicates that longitudinal variation of luminescence are set by sediment input from landscape erosion with minor alongstream bleaching due to transport.
How to cite: Karman-Besson, L., Bonnet, S., Guyez, A., Biswas, A., Carretier, S., Allèbe, M., Harries, R., and Reimann, T.: Imprint of an extreme rainfall event on landscape erosion traced by feldspar single-grain luminescence (Río Ñuble, Chile)., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-4293, https://doi.org/10.5194/egusphere-egu25-4293, 2025.
Channel widening is a major hazard during floods, particularly in confined mountainous catchments. However, channel widening during floods is not well understood and not always explained by hydraulic variables alone. Floods in mountainous regions often coincide with landslides triggered by heavy rainfall, yet landslide-channel interactions during a flood event are not well known or documented. Here we demonstrate with an example from the Great Colorado Flood in 2013, a 1000-yr precipitation event, how landslide-channel feedbacks can substantially amplify channel widening and flood risk. We use a combination of DEM differencing, field analysis, and multiphase flow modeling to document landslide-channel interaction during the flood event in which sediment delivered by landslides temporarily dammed the channel before failing and generating substantial channel widening. We propose that such landslide-flood interactions will become increasingly important to account for in flood hazard assessment as flooding and landsliding both increase with extreme rainfall under climate change. We also demonstrate the role of multiphase models such as r.avaflow in simulation of flood dynamics in cases of high lateral sediment supply and recommend that these are further tested for more accurate modeling of flood hazard in catchments where floods typically coincide with high sediment supply.
This study has been accepted for publication in npj Natural Hazards: Bennett, G.L., Panici, D., Rengers, F.K., Kean, J.W., Rathburn, S.L., Landslide-channel feedbacks amplify channel widening during floods, npj Natural Hazards, https://doi.org/10.1038/s44304-025-00059-6
How to cite: Bennett, G., Panici, D., Rengers, F., Kean, J., and Rathburn, S.: Landslide-channel feedbacks amplify channel widening during floods, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18411, https://doi.org/10.5194/egusphere-egu25-18411, 2025.
Sediment cascades from the high mountains of the Himalaya are initiated in steep glaciated and fluvial landscapes and transfer downstream through alluvial and bedrock reaches of the river network before exiting at the mountain front. Understanding how the stochastic triggers for processes such as landslides, GLOFS and ‘cloudbursts’ translate into downstream hazards such as sediment-rich floods underpins the changing risk profile for communities in these settings. In a collaboration between the UK Natural Environment Research Council (NERC) and the Indian Ministry of Earth Sciences we analyse the downstream translation of high magnitude sediment transport processes in the Ganga catchment of Uttarakhand. A time series of fast-moving shallow, and slower-moving deep landslides are being mapped through automated remote sensing and field-based monitoring. These are then compared to the distribution of wide alluvial reaches of the channel network where potential ‘sediment bombs’ are accumulating. These accumulations of sediment are mapped using high resolution digital topography and their thicknesses measured using seismic nodes. Based on our understanding of how the locations of ‘sediment bombs’ link to potential landslide sediment sources and/or damming effects, we will then explore triggering mechanisms that translate this material downstream as devastating debris and sediment-rich flows; these will be based on physics-based models for landslide and debris flows (LaharFlow) and sediment-rich flood discharges (Caesar Lisflood). Through the analysis of case studies such as the 2013 Alaknanda floods, and model scenarios, we intend to work with local disaster management authorities in developing evolving hazard forecasts ahead of each monsoon. These forecasts of the changing dynamic risk from year to year will aid in the targeted monitoring of upstream processes.
How to cite: Sinclair, H., Sinha, R., Clubb, F., Harvey, E., Milledge, D., Kumar, V., Phillips, J., Sreelash, K., Ensor, J., Verma, T., Chauhan, N., Babu, P., Parsons, D., Creed, M., Naylor, M., Mudd, S., Devrani, R., Sundriyal, Y., Gupta, V., and Gahalaut, V.: Dynamic risk from sediment cascades in the Indian Himalaya, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21687, https://doi.org/10.5194/egusphere-egu25-21687, 2025.
Posters on site: Thu, 1 May, 14:00–15:45 | Hall X3
The short-lived, high-magnitude events have had a significant impact on the geomorphic evolution of the bedrock catchments, but the relative contribution of these episodic events over the high-relief regions is not well understood. The Upper Indus River in the western syntaxial region has witnessed several infrequent episodic and outburst flood incidences. However, the geomorphic imprints of these catastrophic events and their influence on the long-term fluvial processes in the Upper Indus region have not been clearly understood due to a lack of discharge information from these instances of flooding. In this study, we estimate the stream power proxy driven by the channel gradient-discharge product to identify areas of possible anomalous channel erosion and the geomorphic response of the Upper Indus River during two recent anomalous flooding events in the Upper Indus catchment, which occurred in the 2010 and 2022 monsoon periods. The synoptic observations during these two flood events, derived from the HYSPLIT model using the backward trajectory with different heights, indicate that the anomalous precipitation triggering these floods is brought about by a meteorological disturbance. This disturbance involves the interaction of two distinct moisture fluxes, namely the southward moving mid-latitude westerlies troughs and eastward advancing southwestern monsoon circulation. We used topographic metrics to conduct a landscape analysis and calculated the causal relationship between hydroclimatic variables to understand the spatial relationship between the geomorphic response, climatic controls, and primary triggers of these flood events. The topographic analysis indicates that the trunk channel of the Upper Indus River exhibits significant variations in the ranges of the ksn anomaly, χ-gradient, and SL-index, along with frequent sudden rises in stream power profiles across the flooded zone over the low-relief region of Ladakh. Then, when the river traverses through the Nanga Parbat- Harmosh Massif (NP-HM) region along a rapidly exhumed region of the north-western (NW) Himalaya, there is a progressive rise in the local relief and channel gradient, which is also reflected in the spatial distribution of stream power. The spike or transition in the magnitude of the stream power from the Ladakh terrain to the NP-HM region corresponds to the zone of progressive erosion across the active structures. Our study uncovers several significant event characteristics of the Upper Indus catchment's 2010 and 2022 anomalous flood events. Our analysis shows that the 2022 flood originated across elevated glacial channels due to the anomalous temperature rise, which increased the glacial runoff. This increase in runoff across glaciated catchments after traversing through fluvial reaches enhanced the fluvial discharge and likely increased the stream power in the anomalous precipitation region. We observe a statistically significant relationship between the anomalous stream power and relative EVI range across the lower reaches, which serves as a significant geomorphic indicator of change in the channel morphology. These extreme floods illustrate how causal connections between temperature and precipitation across high relief-gradient channels can magnify the impacts. Such hydrological events may play significant roles as efficient geomorphic agents of erosion and, therefore, in the coupling of climate extremes, topography, and surface processes.
How to cite: Kashyap, A., Cook, K. L., and Behera, M. D.: High-mountain floods and landscape perturbation: Geomorphic and hydroclimatic insights of extreme flood events across the Upper Indus catchment in the NW Himalayas, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-576, https://doi.org/10.5194/egusphere-egu25-576, 2025.
Glacial lake outburst floods (GLOFs) are devastating to downstream communities in high mountain Asia. GLOF hazards are difficult to characterize because of the complexity and variability in factors that control susceptibility, such as warming temperatures, rainfall, and slope instability. Compounding this uncertainty is the potential for downstream hazards such as landslide dam outburst floods. The August 16, 2024 Thame GLOF in the Himalaya illustrates how local geomorphology can influence a cascading hazard chain. Initiating in the Thyanbo Lakes near the Tashi Lapcha Pass in the Solukhumbu region of Nepal, the Thame GLOF destroyed at least houses, an elementary school, and a medical clinic in the village of Thame, as well as displacing 135 people due to the debris inundation and burial of a majority of the town’s farmland. As part of a regional project with the Asian Development Bank, BGC Engineering and partnering organizations including Nepal’s National Disaster Risk Reduction and Management Authority and the International Centre for Integrated Mountain Development, visited Thame in December 2024 to assess GLOF risk from the remaining lakes and to inform reconstruction of the village. The team observed several characteristics of the watershed’s geomorphology that affected the triggering conditions and amplified the consequences of this GLOF. First, the GLOF burst through the lower of two adjacent glacial lakes from rapid water displacement, but not outburst, from the upper lake. Second, debris fan and rock avalanche deposits on both sides of the valley floor formed a constriction which ponded during the event, resulting in increased knickpoint erosion, sediment supply, and inundation of Thame. Third, the GLOF down-cut up to 10 meters through glaciolacustrine deposits at the terminus of the valley, triggering retrogressive landsliding that now poses risk to the remaining buildings in Thame. The Thame GLOF highlights the importance of considering geomorphology in assessing the potential magnitude and humanitarian risks of GLOFs, as well as the cascading hazard chain that can develop. Site-specific geomorphic and geologic studies will continue to be valuable in building our understanding of GLOFs and how to assess risk to downstream communities.
How to cite: Hille, M., Mark, E., Strouth, A., Sharma, K., Dixit, A., Zubrycky, S., Scheip, C., and Carter, R.: Field insights from the August 16, 2024 Thame glacial lake outburst flood in Nepal: how geomorphology can affect a cascading hazard chain, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14809, https://doi.org/10.5194/egusphere-egu25-14809, 2025.
This study presents the most comprehensive and recent inventory of glacial lakes in Kyrgyzstan, offering one of the first digitized polygon-based datasets covering the entire country. It examines the dynamics of glacial lakes and glacial lake outburst floods (GLOFs) within the context of rapid glacier retreat and permafrost degradation due to climate change. Using Sentinel-2 imagery acquired during the summer months (July to October) of 2022–2024, this research employs a Python-based workflow in ArcGIS Pro to identify and delineate glacial lakes. A total of 41 atmospherically corrected images with <5% cloud cover were analyzed, ensuring optimal coverage and resolution (10 m), capable of detecting lakes larger than 0.003 km². A threshold of 0.07 from the Normalized Difference Water Index (NDWI) was used to generate an initial water mask. Polygons were refined based on morphological filtering, proximity to glaciers identified in the Randolph Glacier Inventory (within 30 km), and elevation criteria derived from the ALOS Global Digital Surface Model (AW3D30) (>3,000 m a.s.l.). All polygons were manually reviewed for accuracy.
The inventory identifies more than 2000 glacial lakes across Kyrgyzstan. The highest density is found in the Terskey (1,137 lakes) and Kyrgyz (323 lakes) mountain ranges, as well as in the southwestern regions of Osh and Batken, where higher altitudes favor lake formation. Glacial lakes are mainly located between 3,250 and 3,850 meters, with larger lakes typically dammed by bedrock or a combination of damming types. Ice-dammed lakes are more common at higher latitudes, whereas those dammed by landslides are found at lower latitudes. Analysis of optical images from 2023 and 2024 revealed lakes newly formed or enlarged, underscoring the rapid evolution of these features due to glacier retreat and the crucial need for regular inventory updates.
This inventory outlines the spatial distribution and physical characteristics of glacial lakes, as well as those most at risk of GLOFs. As highlighted in previous studies, most endangered lakes fall into three genetic categories: moraine-glacier lakes, supraglacial lakes, and those dammed by landslides and debris flows. Adygine and Kol-Ukok lakes were selected as case studies to illustrate these hazardous types. Fieldwork conducted in August 2023 and 2024, including drone and geophysical surveys, validated the dataset and provided insights into the geomorphological and geological factors influencing lake stability, including the role of permafrost in slope dynamics. Drone imagery revealed key surface features, enhancing understanding of the local context and informing future assessments of potential instability. Semi-automated mapping is a valuable tool for hazard assessments, but limitations persist. Shadows, cloud cover, seasonal water-filled depressions, and residual snow can cause false positives, while terrain complexity and variations in water turbidity or sediment loads affect accuracy. Manual verification remains essential to ensure reliability.
This national glacial lake inventory provides the basis for future studies, highlighting the roles of climate change and geology in shaping vulnerable mountain systems. By integrating regional-scale remote sensing data with fieldwork, this approach strengthens hazard assessments by providing crucial local context in high-risk areas, ensuring more reliable analyses.
How to cite: Piroton, V. and Havenith, H.-B.: National Inventory of Glacial Lakes in Kyrgyzstan: Integrating Remote Sensing for Hazard Assessment and Local-scale Monitoring, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-19362, https://doi.org/10.5194/egusphere-egu25-19362, 2025.
Hydropower projects across the High Mountain Asia (HMA) region have attracted substantial investment in recent decades, with institutions such as the World Bank and the Asian Development Bank funding projects worth hundreds of billions of dollars. However, hydropower development in this region faces severe challenges from natural hazards, particularly rock and/or ice avalanches (RIAs) and their cascading processes. RIAs can produce between 10 million and 100 million cubic meters of sediment—equivalent to 2% to 20% of the Yangtze River’s annual sediment transport. These mass flows are sudden, powerful, and come with little warning, posing major and long-lasting threats to hydropower installations (HPIs), local communities, and river systems. A notable example is the 2021 Chamoli disaster in India, which destroyed two hydropower projects, killed more than 200 people, and impacted downstream areas over 50 kilometers away.
To mitigate economic losses, optimize investments, and enhance hydropower planning in HMA, this study evaluates the potential risk of RIAs to HPIs across the region. A comprehensive dataset of HPIs, including dams, intakes, and powerhouses, was compiled for this purpose. Potential RIA hazards were assessed by analyzing all steep slopes within glacial and periglacial domains, with downstream trajectories to HPIs calculated. This assessment utilized an iterative GIS-based model, designed to automatically assess the risk to each HPI and enable large-scale automated applications.
Our results show that there are currently 1,819 HPIs in the HMA, around 53% (968) of which are threatened by RIAs and their cascading processes. With ongoing hydropower development, the number is planned to increase to 2,611 in the future, with those at risk rising to 57% (1,413). High- and very high-risk HPIs are predominantly concentrated along the Ganges River basin, particularly in Nepal, where a 3-fold increase in future risk is anticipated, including within critical transboundary hotspots. Compared to GLOFs, potential RIAs starting zones are more numerous and unpredictable, while in combination, RIA’s can initiate devastating cascading process chains from glacial lakes, amplifying risk to HPIs. To ensure sustainable development, future hydropower planning in the HMA region must account for the threat of RIAs, emphasizing strategic site selection, appropriate HPI types, and enhanced risk management strategies.
How to cite: Zhong, Y., Allen, S., Bu, X., Upadhyay, K., Kargel, J., Steiner, J., Zheng, G., and Stoffel, M.: Cascading rock and ice avalanches are a widespread threat to High Mountain Asia hydropower installations, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15938, https://doi.org/10.5194/egusphere-egu25-15938, 2025.
Debris flows are among the most common natural hazards in mountainous regions, with the potential to severely impact human lives and infrastructure. In the vicinity of the Alpe di Succiso Mountain (Northern Apennines, Italy), several debris flows have been documented, impacting trees in the upper portion of the forest. As the precipitation events can become more intense in relation to climate change, assessing the spatial distribution through time of these debris flows is essential for modeling their occurrence and for effective hazard assessment.
In the context of the DECC project (2023), on the N-facing slope of the Alpe di Succiso we set up a multidisciplinary research comprising geomorphology, dendrochronology, geopedology, hydrological monitoring and climatology.
Geomorphic processes of different types (glacial, gravitational and torrential) characterize the area and have shaped landforms and deposits since the late Quaternary (Rashid et al., 2024).
Being the soil a useful archive of forming factors leading to its development, two different soil toposequences (one along a stable slope and one along the slope affected by debris flow) have been selected and analysed using a geopedological approach. The study of the spatial variation of soil profiles in relation to their position along the slope allows the reconstruction of both the stability and instability phases that characterise the slope over time and the impact of debris flows on soil development.
The first results coming from the four hydro-pedological stations show that all the monitoring points respond quickly to precipitation, highlighting the presence of a highly permeable soil. During the summer season, thanks to high temperatures and relatively sparse rainfall events, the soil tends to dry out after rain. However, in early autumn, due to the drop in air temperatures and more frequent and intense rainfall events, it consistently exhibits conditions of complete saturation for extended periods.
Based on dendrogeomorphological analysis and orthophotos, the debris flow events were classified into major and minor categories. The 1975 and 1987 events were classified as major, while the 1997, 2003, and 2013 events were considered minor.
Debris flow events were further correlated with precipitation records from various sources, including hydrological yearbooks, nearby weather stations, and rain gauge based and reanalysis gridded datasets. In this context we are investigating several rainfall events which could have triggered debris flows through time.
References
DECC, 2023. DECC - Debris flow hazard and climate change in the Northern Apennines: reconstructing and modelling past and future environmental scenarios. PRIN 2022 PNRR - Projects of Great National Interest, Financed by the European Union – Next Generation EU. https://x.com/DECC_project/
Rashid et al., 2024. Journal of Maps. https://doi.org/10.1080/17445647.2024.2422549
How to cite: Leonelli, G., Arcuri, B., Brunetti, M., Chelli, A., Manara, V., Masseroli, A., Maugeri, M., Melada, J., Pescio, S., Petrella, E., Rashid, M. A., and Trombino, L.: Reconstructing the occurrence of debris flows through time in the surrounding of Alpe di Succiso Mt., Northern Apennines (Italy): a multidisciplinary approach in the context of climate change, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-11632, https://doi.org/10.5194/egusphere-egu25-11632, 2025.
Extreme rainfall events in mountain catchments can induce substantial geomorphic changes, reshaping channels, hillslopes, and surrounding environments. These changes often widen active channels, recruiting large wood from adjacent forests into sediment-laden flows, thereby increasing hazards such as altered flow patterns, sediment retention, and logjam formation. Such dynamics can exacerbate flood risks, particularly near infrastructure like bridge piers, dams and weirs. Understanding the extent of forest areas contributing to large wood recruitment and predicting mobilized large wood volumes is critical for effective hazard mitigation. This study examines the geomorphic response of the Vésubie catchment (392 km², south-east, France) to Storm Alex (October 2020), which caused intense flood and sediment transport (i.e., bedload, debris floods and debris flows) with strong large wood recruitment. Using high-resolution aerial LiDAR data from pre- and post-storm surveys, geomorphic changes in valley bottom channels and 43 tributaries (catchment sizes: 0.06–59 km²) were analysed at both catchment and 100-m reach scales via the DEM of Difference (DoD) technique. Diachronic canopy height models were used to assess forest cover loss, and the volume of recruited large wood was estimated based on data from the French national forest inventory. Results revealed massive sediment mobilization, with sediment net balances ranging from -669 m³ ± 36 m³ to -341,575 m³ ± 3,625 m³ in tributaries and -518,609 m³ ± 5,735 m³ to 326,213 m³ ± 16,912 m³ in valley bottoms. This culminated in a total sediment export of 2.14 Mm³ ± 48,985 m³ from the Vésubie catchment. Tributary erosion volumes varied by an order of magnitude, displaying spatially consistent patterns in tributaries with pronounced variability in valley bottom channels. Erosion rates showed no distinct trend with slope, with high rates observed also at low gradients. Conversely, deposition rates increased with decreasing slopes (<25%) but declined sharply in steeper channels, emphasizing the critical role of slope in sediment connectivity. Erosion rates varied widely (0.1–2.5 m3/m2) across the cascading network, reflecting diverse geomorphic responses and exceptional sediment mobility during Storm Alex. The absolute and relative reduction of forest cover extension inside the reaches well correlated with local sediment erosion, deposition, and net balance rates per unit length of reaches, indicating dependence on the intensity of geomorphic processes. The process type played a minor role. The estimated large wood volumes recruited during Storm Alex in the tributaries ranged from moderate to high when compared to literature values, while system-wide estimates exceeded the highest predictions of large wood volumes when scaled to the catchment surface. The findings provided by this extensive dataset underscore the need to integrate geomorphic and large wood dynamics into hazard assessments and protection measures in mountainous regions, particularly in case of extreme events.
How to cite: Martini, M., D'Agostino, V., and Piton, G.: Geomorphic Response and Large Wood Recruitment in the Vésubie Valley (France) Following Storm Alex, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9727, https://doi.org/10.5194/egusphere-egu25-9727, 2025.
Hazards may arise not only from inundation and the direct effects of the flowing water but also from the physical impacts of sediment movement, erosion, deposition, and the resulting destruction. Major geomorphological changes in channels occur during flood events, and one of the important questions is how big floods impact sediment flux and landscape changes overall. For this reason, it is important to study the effects of extreme floods on fluvial dynamics. The key concept is the sediment connectivity within a river catchment that can be used to explain the continuity of sediment transfer from a source to a sink and the movement of sediment between different zones of a catchment. This work aims to analyse the complex interactions of the elements that play an important role in the morpho-fluvial system, bearing in mind a series of cascading processes that can be triggered during an extreme rainfall event. A study was conducted on the small catchment area of the Tenetra creek, which is located in a mountainous area of the Marche region and whose physical conditions of geomorphological evolution are similar to an Alpine environment. This area was affected by a flood event in September 2022, triggered by an intense rainfall of about 419 mm in 12 hours, that caused an intense mobilisation of the material towards the valley floor and the main watercourse. The rainfall event also activated several highly mobile landslides, most represented by debris flows, that sometimes reached the river network, contributing to the increase in the river solid transport. The sediment transport analysis in the study area was structured with an integrated methodology based on different techniques developed individually by various authors for different environmental contexts. Focusing on the origin of the material to be able to define the availability as well as the productivity of the sediment, and secondly quantifying the material for a better understanding of the changes in the hydro-morphological. The slopes were analysed using Cavalli's connectivity index, which, using free, stand-alone GIS-based software, assesses the potential connection between the slopes and the land elements chosen as the target for analysis, in our case the main hydrographic network. Applying Geomorphic Change Detection (GCD) software, it was possible to quantify the difference between two high-resolution (1x1 m LIDAR-derived) Digital Terrain Models used to estimate the volume involved and to study river morphological dynamics through lateral and vertical variations. Iber Software, a two-dimensional numerical tool designed for simulating free surface flow in rivers, was employed to investigate erosion and deposition processes in Tenetra Creek. Iber solves the full depth-averaged shallow water equations to compute water depth and velocity. The sediment transport module within Iber is used to model bedload transport, applying the Meyer-Peter and Müller equation. The results explore the role of sediment availability and supply in a catchment basin through the study of connectivity, seeking to understand the relationships established between different types of processes. Through scenarios with different supplies, we set up to understand the impact of morphodynamic change during an extreme event.
How to cite: Guidi, E., Pappafico, G. F., Ottaviani, F., and Morelli, S.: Hydro-morphological changes and sediment supply investigation: a case study in an Alpine-type river catchment (Marche, Italy), EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13029, https://doi.org/10.5194/egusphere-egu25-13029, 2025.
The Himalayan region hosts some of the world's most dynamic river systems, characterized by steep gradients, high sediment loads, and susceptibility to geomorphic changes. Recent advances in computational modeling techniques have revolutionized our ability to understand and predict morphodynamic processes in these challenging environments. The study presents an integrated approach that combines comprehensive hydrological data with machine learning and numerical modeling techniques to improve forecasting accuracy and advance our understanding of complex hydrological phenomena. The integration of these methods enables a more robust and comprehensive analysis of hydrological systems, incorporating diverse datasets such as precipitation, soil moisture, streamflow, and land cover characteristics.
Physics-based models using computational fluid dynamics (CFD) enable detailed simulations of flow patterns, sediment transport, and erosion-deposition dynamics in rivers. By integrating topographic data, hydraulic parameters, and sediment characteristics, these models predict changes in channel morphology over time. Particle-based simulations like discrete element methods (DEM) and smoothed particle hydrodynamics (SPH) provide insights into water-sediment interactions, capturing granular flow behavior and sediment sorting crucial for understanding channel evolution. Coupled hydro-morphodynamic models combine hydraulic simulations with morphological feedback, considering the mutual influence between flow dynamics and channel morphology. These models account for sediment transport feedback, bank erosion, meander dynamics, and delta formation, offering a holistic view of river evolution. Advancements in data assimilation, including remote sensing and in-situ measurements, enhance model calibration and validation, improving prediction reliability. Machine learning algorithms like neural networks, decision trees, and support vector machines extract patterns from large hydrological datasets, enhancing forecasting accuracy. Integrated with numerical simulations, these models predict hydrological processes across scales, demonstrated through case studies showcasing improved forecasting and dynamics capture. This integrated approach aids in water resource management, flood forecasting, and climate change assessments, facilitating informed decision-making in water-related sectors.
These computational modeling advances have significant implications for Himalayan river management, natural hazard assessment, and climate change impact studies. They provide valuable tools for predicting sediment transport, erosion hotspots, and morphological changes, aiding in sustainable river basin management and ecosystem conservation efforts. However, challenges remain in integrating complex geomorphic processes, scaling models across different spatial and temporal scales, and incorporating uncertainties for robust decision-making in dynamic Himalayan river systems.
How to cite: Nath, S., Shekhar, S., Dikshit, O., and Nagarajan, B.: Advances in computational modeling for morphodynamics in himalayan rivers, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14955, https://doi.org/10.5194/egusphere-egu25-14955, 2025.
The availability of reliable hourly time series is essential for investigating the link between precipitation and debris flow events. However, before the 1990s data from weather stations are generally only available at daily resolution.
A methodology is proposed to reconstruct hourly precipitation time series from the 1940s by combining ERA5 reanalysis data — which provide hourly information — with daily cumulative values measured by in situ stations. The goal is to provide complete hourly series capable of capturing the intense precipitation events that may trigger debris flows, as required by the DECC (2023) project which investigates these gravitative phenomena at the multi-decadal scale for a study site in the area of Alpe di Succiso Mt., Northern Apennines (Italy). The analysis through time of these disruptive phenomena characterized by the rapid movement downslope of a mixture of water, rocks and debris, is a fundamental step for the hazard assessment in the context of climate change.
The algorithm automatically selects the best daily aggregation window by correlating ERA5-summed hourly precipitation with observed daily totals. ERA5’s hourly data are then corrected to match daily observed precipitation and finally ERA5’s hourly corrected data are scaled to match the distribution of the rain gauge hourly data which are available for the study area for the last decades both as station data and as gridded fields.
Daily rain gauge-based precipitation data were collected for an area within a 50 km radius from the study site from multiple regional and national providers and subjected to rigorous analysis to ensure quality and consistency. Redundant series were removed, and data were merged to establish a unique correspondence for each location. Metadata verification included checks for consistency in location coordinates and altitude, complemented by manual validation. The final dataset consists of 403 stations and was analyzed alongside gridded daily precipitation data (available from 1961) and hourly precipitation data (available from 1991), provided by the Regional Agency for Prevention, Environment, and Energy of Emilia-Romagna.
The final reconstructed hourly series is validated by comparing it with hydrological yearbook data and, for more recent periods, with rain gauge-based gridded data and hourly observations from the same stations. The reconstructed hourly series is then used in a multi-temporal analysis of dated debris flow events in Alpe di Succiso to investigate magnitude-frequency relationships and potential triggering thresholds.
References
DECC, 2023. DECC - Debris flow hazard and climate change in the Northern Apennines: reconstructing and modelling past and future environmental scenarios. PRIN 2022 PNRR - Projects of Great National Interest, Financed by the European Union – Next Generation EU. https://x.com/DECC_project/
How to cite: Melada, J., Arcuri, B., Manara, V., Brunetti, M., Chelli, A., Leonelli, G., Pescio, S., Petrella, E., Rashid, M. A., Trombino, L., Masseroli, A., and Maugeri, M.: An hourly precipitation approach to debris flow hazard assessment in the DECC project: leveraging daily rain gauge observations and hourly ERA5 reanalysis data, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16938, https://doi.org/10.5194/egusphere-egu25-16938, 2025.
Landslides pose significant hazard in mountain regions, driving hillslope erosion and mobilizing large amounts of sediment to rivers. Earthquake-triggered landslides are commonly clustered near ridges and steep slopes, influenced in part by the topographic amplification of seismic waves. Understanding the spatial distribution of these landslides is critical for evaluating sediment supply to river and connectivity. While several complex physical-based models have been developed to explore the spatial distribution and river connectivity of earthquake-triggered landslides, challenges remain in accurately modeling the influence of earthquake-induced ground acceleration.
Here we test Slipos, a simple physic-based model accounting for landslide source and a runout, to study the impact of ground acceleration from the 2015 Mw 7.8 Gorkha earthquake on the spatial distribution of landslides and their connection to rivers. The landslide source component of Slipos is calibrated by varying rock strength parameters, while the runout component is refined by exploring transport-deposition parameter spaces.
Preliminary results show some discrepancies between modeled and observed landslides, in terms of location and source volume. We infer that the noise affecting post-event DEM lead to unrealistic landslides. Integrating peak ground acceleration leads to an increase in the area and volume of each individual landslide. However, the runout component accurately reproduces observed landslide locations when parameter spaces are appropriately adjusted. Initial findings on landslide connectivity indicate that up to 70% of modeled landslides deposit material in proximity of a river channel, consistent with observations. Our preliminary results highlight the need to use high-quality and high-resolution DEM when modeling earthquake-triggered landslides. In addition, the Slipos model, particularly its runout component, has the potential to accurately reproduce landslides connectivity.
How to cite: Desormeaux, C., Steer, P., and Clark, M.: Assessing the Impact of Ground Acceleration during Earthquake on Landslide Triggering Using a Simple Physic-Based Model : Application to the 2015 Gorkha Earthquake, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18220, https://doi.org/10.5194/egusphere-egu25-18220, 2025.
