While intensifying extreme rainfall is projected to substantially increase future flood hazard, climate forcing alone does not fully explain observed and emerging risk patterns. Morphodynamic processes, floodplain connectivity, changes in inundation frequency, and sea-level rise play fundamental roles in controlling flood behaviour and impacts. Similarly, geohazards arise from complex interactions among climate variability, land-use change, tectonic activity, and geological processes across diverse environments.
Recent advances in remote-sensing technologies, particularly Interferometric Synthetic Aperture Radar (InSAR) and Unmanned Aerial Vehicles (UAVs), have transformed the monitoring of ground deformation, slope movements, and terrain instability. These tools complement field observations, experimental approaches, and numerical modelling, enhancing our ability to detect, understand, and anticipate hazardous processes.
This session invites interdisciplinary contributions examining how rivers, hillslopes, and landscapes respond to hydrological, geomorphological, and climatic drivers, and how human interventions (including flood defences, managed floodplains, hard engineering, and land-use planning) amplify or mitigate hazard and risk. We particularly encourage studies addressing morphodynamic controls on flood hazard, climate-driven hazard trends across diverse environments, patterns and drivers of flooding and landslides, and innovative monitoring and modelling approaches that support resilience and sustainable decision-making in hazard-prone regions.
Orals: Fri, 8 May, 16:15–18:00 | Room -2.20
Geomorphic transitions—such as the interface between rivers and floodplains—are critical zones controlling water, sediment, and nutrient transport. River–floodplain connectivity often occurs through secondary channels that convey fluxes into the floodplain. In other cases, connectivity is created or amplified by human interventions. But is higher connectivity in a landscape always beneficial?
In this talk, we examine the role of connectivity—both structural and functional—in shaping flood wave attenuation and long-term land change. We draw on two contrasting landscapes. First, in the Trinity River (Texas), rivers and floodplains are connected via floodplain channels. Using an idealized model, we show that attenuation transitions from connectivity-limited to storage-limited as discharge increases. Secondary channel conveyance promotes early floodplain inundation and attenuation at lower flows, but at higher flows it can fill storage rapidly and even increase downstream flood peaks. Greater conveyance and wider floodplains increase fluxes to the floodplain, yet conveyance shortens residence times while wider floodplains prolong them.
Second, we examine coastal Louisiana: the sediment-rich Wax Lake Delta, which is gaining land, and the sediment-starved Terrebonne Bay, which is losing land. Here, connectivity plays opposite roles—enhancing resilience and land growth in one system while accelerating degradation in the other.
This work shows that connectivity is not universally “good”: it can attenuate floods and build land under some conditions, but under others it transfers risk or drives loss. Understanding these dynamics is critical for designing floodplain reconnection and managing landscapes under climate change.
How to cite: Passalacqua, P., Tull, N., and Wright, K.: When connectivity helps and when it hurts: How natural vs. human-induced connectivity affect flood wave attenuation and land change, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7550, https://doi.org/10.5194/egusphere-egu26-7550, 2026.
Densely populated coastal deltas worldwide face cascading flood hazards associated with sea-level rise, storm surges, dwindling sediment supplies, and land subsidence. One of the greatest hurdles to hazard prediction stems from this last component—land subsidence—which can vary drastically in space and time for a given delta. Here we constrain subsidence variations on the Ganges Brahmaputra Delta, using a state-of-the-art 1D compaction model based upon fundamental principles of porous-media mechanics and groundwater flow; as well as constitutive relations for porosity and edaphic factors (e.g., plant roots, animal burrows). The model accurately reproduces field observations (GNSS, RSET-MH, optical-fiber compaction meters, auger cores), showing compaction-induced subsidence rates of 1–30 mm/y depending upon local thickness and lithology of underlying Holocene deposits, forest tree density, and sedimentation rate. Sedimentation drives a dynamic compaction response over timescales of 10–100 years, such that floodplains cut off from sediment after embankment construction in the 1960s have undergone significant elevation loss, but are now experiencing a gradual subsidence slowdown. Some of the fastest subsidence rates can be attributed to buried Pleistocene paleovalleys infilled with thick Holocene sediments, portending a legacy of ancient sea-level changes on future flood hazards. Updated coastal flooding estimates informed by our model indicate that compaction-induced subsidence will be responsible for up to 50% of twenty-first-century relative-sea-level rise, and exert a first-order control on flooding hotspots. This predictive subsidence model can improve assessments of coastal flood risk on the Ganges-Brahmaputra and other deltas worldwide; and help inform ongoing billion-dollar restoration efforts facing crucial decisions as to where and when coastal barriers, sediment diversions, and settlement relocations should be implemented in the coming century.
How to cite: Chadwick, A. J., Steckler, M. S., Wilson, C. A., Goodbred, S. L., Camargo, S. J., Rahman, F., Rana, Md. M., Akter, S., Bhuiyan, A. H., Larochelle, S., Hossain, Md. J., Mahmud, S. S., Tanvir, A. A., Ahmed, Z., and Mim, A.: Predicting land subsidence and cascading flood hazards on deltas in the twenty-first century , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13811, https://doi.org/10.5194/egusphere-egu26-13811, 2026.
Dike breaching following overtopping event is considered as one of the most common failure mechanisms. Understanding this process is critical, as breaches typically result in catastrophic flooding. While overtopping failures have been studied both experimentally and numerically, the coupled physical mechanisms remain complex. Erosion associated with high-velocity water flowing downstream has often been considered as the main leading cause of failure. Yet, suction pressure and water content fluctuations provide additional strength to the dike material. The effects of suction on the geomechanical strength of the dike material have often been disregarded.
In this work, we propose a proof-of-concept of a numerical model that encompasses what we consider as the main physical processes occurring during dike overtopping. First, we solve, in a traditional hydraulics approach, the Shallow-Water-Exner equations system to evaluate the water flow and the erosion potential. Second, we solve the Richards equation, for groundwater flow evaluation. This provides the information on the suction pressure evolution in the dike, spatially and in time, subject to overtopping. Third, we propose a geomechanical approach that accounts for suction pressure effects on the mechanical strength of the soil. Large displacements of the geomaterial are computed by means of the Particle Finite Element Method (PFEM). It is a Lagrangian based method, that relies on a very efficient remeshing algorithm to simulate large displacements.
The resulting model is a proof-of-concept for advanced dike failure simulation. We compare the outcome of the model in a dike failure theoretical case with a purely hydraulic based model and with a sediment transport-based model. The analysis focuses on the differences between these models, as reflected in the output hydrographs. The aim is to underline the need for tightened coupling between hydrodynamic, sediment transport and geomechanical processes to accurately simulate dike breaching events and improve hydrograph prediction.
How to cite: Delpierre, N., Soares-Frazão, S., and Rattez, H.: Coupled Hydro-Geomechanical modelling of dike breaching, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-6610, https://doi.org/10.5194/egusphere-egu26-6610, 2026.
The Ahr flood of 2021 had severe consequences, including 135 fatalities, extensive damage to infrastructure and buildings, and significant geomorphologic change. Clogging of bridges exacerbated water levels, leading to outburst flooding on top of high water levels when the bridges failed. The clogging of bridges was mostly due to large woody debris. Thus, the question arose as to where and when the large wood (LW) was sourced. This study aims to analyse and quantify the recruitment of LW during this extreme event in a lower mountain range with a return period of more than 500 years.
LW with a crown diameter greater than 2 m was mapped across the floodplain of the Ahr river using aerial images and orthophotos from 2019, 2021, 2022, 2023 and 2025. This approach enabled us to determine how much LW was uprooted, washed away or merely tilted by the flood. Furthermore, it provided data on how much LW was cut by humans after the flood (Zmelty and Büchs, 2025). Information on LW properties, including tree height, was obtained from 1 m LiDAR data (2019, 2021 and 2022). Canopy height models (CHM) of the valley floor and resulting CHM of Difference (CoD) data sets were calculated for all time slices. The causes of LW recruitment were analysed using the water levels and flow velocity of the 2021 flood (Vorogushyn et al., 2025).
Manual mapping revealed that 12,499 woody structures were uprooted, 4,424 were tilted and 2,763 were cut by humans after the event. Preliminary analysis of LiDAR data shows that the location of the removed LW fits relatively well with the manual mapping, considering the distortion between the different aerial images and orthophotos. The LiDAR results show that 5,397 trees were between 5 and 10 metres high and 3,556 trees were higher than 10 metres. Preliminary analyses indicate a correlation between LW recruitment and modelled water levels and flow velocities. However, the LW data needs to be cleared of trees cut by humans and differentiation between uprooted and tilted trees is necessary. In any case, the results demonstrate the extreme uprooting of trees by the 2021 flood in the lower mountain range. The missing trees have seriously altered the ecological condition of the floodplain, left the river and riverbanks unprotected, leading to increased bank erosion and river warming during the summer.
Vorogushyn, Sergiy; Han, Li; Apel, Heiko; Nguyen, Viet Dung; Guse, Björn; Guan, Xiaoxiang; et al. (2025): It could have been much worse: spatial counterfactuals of the July 2021 flood in the Ahr Valley, Germany. Natural Hazards and Earth System Sciences. 10.5194/nhess-25-2007-2025
Zmelty, A. & Büchs, W. (2025): The ecological potential of a flood disaster - opportunities and failures after the heavy rainfall event in the Ahr Valley in 2021. - Das ökologische Potential einer Flutkatastrophe - Chancen und Versäumnisse nach dem Starkregenereignis im Ahrtal 2021. Decheniana (Bonn) 178: 185–214.
How to cite: Bell, R., Zmelty, A., Dietze, M., Vorogushyn, S., Apel, H., and Schoch-Baumann, A.: Large wood recruitment during the extreme 2021 Ahr flood (Germany), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-18461, https://doi.org/10.5194/egusphere-egu26-18461, 2026.
On 23 September 2023, a major quick-clay landslide occurred at the Stenungsund interchange on the E6 highway in southwestern Sweden. It caused extensive damage to critical transport infrastructure, resulting in long-term regional disruption and underscoring the societal vulnerability of development in sensitive clay terrains. This study presents an integrated geological, geomorphological, hydrological, and anthropogenic analysis of the Stenungsund landslide, aiming to clarify the mechanisms that led to failure and to extract lessons relevant for hazard assessment and land-use planning.
The landslide affected approximately 15 hectares, with a runout distance of about 620 m and an estimated displaced volume of ~1.85 million m³. We combine field mapping, stratigraphic logging, geotechnical data, historical documentation, and LiDAR-derived terrain models with aerial and satellite imagery and hydrological modelling to reconstruct pre-failure conditions, failure kinematics, and post-event morphology. The geological setting consists of thick sequences of late- to postglacial marine clay in a fracture-valley landscape, interbedded with permeable silt, sand, shell-rich horizons, and glaciofluvial sediments. These conditions promote groundwater flow, clay pore-water salt leaching, and the development of quick clay.
Our results indicate that failure initiated at depth within weak clay layers beneath recently placed fill and evolved into a translational progressive landslide. Anthropogenic loading from construction activities acted as the primary trigger, while altered drainage and groundwater pathways raised pore-water pressures. Hydrological modelling shows that excavation, blasting, and filling redirected runoff toward the site and increased infiltration along fractured bedrock and permeable sediment layers. Heavy rainfall in the days before the event likely added to the pressure build-up and influenced the timing of failure. Once downslope resistance was lost, rapid mobilization of quick clay produced large horizontal displacements and complex deformation patterns, including subsidence, heave, and circular-cylindrical failures.
The Stenungsund case highlights the tight coupling between geological predisposition and human modification in quick-clay terrain. It shows how short-term construction activity can destabilize systems that may appear stable under conventional assessments. Integrated evaluations that consider hydrogeological connectivity, stratigraphic variability, and cumulative anthropogenic effects are needed to improve risk mapping and guide controls on loading and drainage changes. Enhanced monitoring of groundwater conditions is likewise essential. As extreme rainfall events become more frequent, reassessing design methodologies and land-use practices in sensitive clay landscapes become increasingly important.
How to cite: Öhrling, C. and Fredin, O.: The Stenungsund (Sweden) Quick-Clay Landslide of 2023: Anthropogenic Influence and Infrastructure Consequences, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-4567, https://doi.org/10.5194/egusphere-egu26-4567, 2026.
Human activities are transforming tropical mountain landscapes at unprecedented rates through deforestation, agricultural expansion, and urbanization. These changes amplify the frequency and magnitude of geo-hydrological hazards such as landslides. While shallow, rapid landslides are well documented, the controls on the activity and dynamics of large, slow-moving landslides (SML) remain much less understood, despite their persistent impacts on communities and sediment dynamics.
This study demonstrates how the combined use of radar and optical Earth observation data enables the detection, mapping, and monitoring of deep-seated landslides across vast and remote tropical regions such as the Albertine Rift. By mapping and comparing more than 120 active and 3,000 historical landslides distributed along the ~1,500 km Rift branch, we reveal how climatic, lithological, tectonic, and anthropogenic factors jointly control their occurrence.
We further analyse multi-year landslide dynamics across contrasting environments, supported by unique ground-based validation datasets built on years of fieldwork in the region, and provide detailed insights into failure mechanisms of recent catastrophic landslides in the area. Altogether, this work delivers a unique regional-scale assessment of SML activity in tropical environments and highlights how landscape and human-driven land use changes can modulate their behaviour. It offers new perspectives on how environmental transformations shape landscape evolution, geo-hydrological hazards and sediment transfer in rapidly changing mountain regions.
How to cite: Dille, A., Vanmaercke, M., Mugaruka Bibentyo, T., Provost, F., Smets, B., and Dewitte, O.: Unstable Slopes and Shifting Landscapes: Slow-moving landslides in the East African Rift, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17413, https://doi.org/10.5194/egusphere-egu26-17413, 2026.
Multiple landslides triggered by heavy rain, associated with debris flows and flash floods are major geohazard in the mountainous areas of Northern Vietnam, resulting in lost of life and property. Mapping landslides immediately after their occurrence remains crucial for providing a better understanding of their causes , the course of their formation, and the influence they exert on both nature and human.
We analyzed the effects of several landslide events that occurred between 2020 and 2024 in Northern Vietnam. We aimed to develop a fully automated geospatially integrated software workflow for rapid and accurate mapping of landslide and debris flows in the subtropical zone. The method we applied was Change Vector Analysis (CVA), which is based on detecting changes betweeen two images (pre- and post-event) by emploing two metrics: magnitude, referring to the amount of change between pixels, and direction, describing the type of change. As input data, we used the Sentinel 2A optical imagery with a spatial resolution of 10 m. For each landslide event we analyzed a separate area, where its geomorphic effects were the most robust. As the exact dates of landslide events varied for each study area, we downloaded pre- and post-event image pairs for each area with different acquisition dates and low cloudiness (below 10%). Due to the mountainous terrain and the potentially disruptive influence of atmospheric correction, we decided to use L1C data. For validation, we used the landslide vectorization polygons. For each study area, we generated random points labeled as “landslide” or “no landslide” based on the landslide polygons. Then, we performed CVA parameter tuning for each area and selected the CVA variant most effective at landslide delineation. We integrated the entire workflow into R script. The results indicate that simple data analysis methods such as CVA can be efficient for landslide mapping. Despite the cloudiness limitation, optical Sentinel-2 data can be applied in the subtropical zone to map the landslides and debris flows.
The study has been supported by the Polish National Science Centre (project no 2023/49/B/ST10/02879).
How to cite: Godziek, J., Pawlik, Ł., and Hieu, T. T.: The Northern Vietnam landslide events mapped with Change Vector Analysis, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14135, https://doi.org/10.5194/egusphere-egu26-14135, 2026.
Landscape evolution principles provide a conceptual framework for understanding how relief develops through long-term interaction of tectonics, climate, and surface processes. In tectonically active mountain regions, these interactions strongly influence the spatial distribution and recurrence of hydrogeomorphological hazards affecting human settlements (Winckell et al., 1997).
The objective of this research is to evaluate the role of landscape evolution as a control factor in flood and landslide hazards within the central Paute River basin, with particular attention to tectonic structures, hydrogeomorphological adjustments, hillslope dynamics, and their interactions with anthropogenic environments. The analysis combines multiple source and scale datasets, including a detailed mass-movement inventory derived from historical images and official cartography from the Geographical Institute of Ecuador (SIGTIERRAS, 2014) and the National Secretariat for Risk Management (SNGRE, 2024). These data were complemented with high-resolution unmanned aerial vehicle (UAV) surveys conducted annually in identified active sectors, which enable documentation of recent reactivations and relevant geomorphic changes.
Results show that floods and landslide hazards are strongly conditioned by long-term landscape evolution. The valley orientations controlled by structures and the inherited sedimentary environments condition the floodplain development and recurrent overbank flooding along the Burgay, Déleg, and Paute Rivers; particularly in the cities of Biblián, Azogues, Déleg, and Paute, provide a clear example of how un-equilibrated base-level conditions influence the hazard (Torres et al., 2022; Torres Ramírez, 2022). Landslide activity is mainly concentrated on slopes shaped by lithological contrasts, tectonic discontinuities, and the presence of previous landslides (Torres-Ramírez & Marco-Molina, 2025), as demonstrated by large-scale events such as La Josefina in 1993 (Plaza & Egüez, 1993), with rainfall acting as a trigger mechanism rather than a primary cause.
These findings reveal that floods and landslides in the central Paute River basin are direct expressions of an evolving landscape in which human settlements are located. Identifying geomorphic controls on hazardous processes provides a better understanding of risk patterns and supports more informed landscape approaches to land-use planning and hazard management in intermontane Andean regions.
Keywords: Landscape evolution, Hydrogeomorphology, Landslides, Floods, Paute river basin, Ecuador
References:
Plaza, G., & Egüez, A. (1993). Consideraciones Geológicas-Geotécnicas sobre el Deslizamiento de La Josefina. Coloquio científico El deslizamiento de La Josefina.
SIGTIERRAS. (2014). Mosaicos de ortofotos a nivel nacional. Sistema Nacional de Información de Tierras Rurales e Infraestructura Tecnológica. Quito, Ecuador. https://bit.ly/2twJiRn
SNGRE. (2024). Database Eventos Registrados. Secretaría Nacional de Gestión de Riesgos y Emergencias, Ecuador. Periodo 2010 a 2024.
Torres, R., Sánchez, E., & Marco, J. (2022). Análisis de la dinámica fluvial del río Burgay al norte de la ciudad de Azogues (Ecuador) y su influencia en el medio urbano mediante técnicas fotogramétricas y TWITTER API. XVII Coloquio Ibérico de Geografía, 332–343.
Torres Ramírez, R. (2022). Estimación morfométrica de la erosión lateral del río Burgay producida por las precipitaciones del 20 de abril de 2022. http://rua.ua.es/dspace/handle/10045/123388
Torres-Ramírez, R., & Marco-Molina, J. (2025). Inventario de movimientos en masa en la zona centro de la cuenca del Río Paute. Avances de La Geomorfología Española En 2023 - 2025.
Winckell, A., Zebrowski, C., & Sourdat, M. (1997). Las regiones y paisajes del Ecuador (Segunda Ed.). CEDIG.
How to cite: Torres-Ramírez, R. and Marco-Molina, J. A.: Landscape evolution as a key driver of flood and landslide hazards: tectonic and hydrogeomorphological evidence from the central Paute River basin, Ecuador, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-14983, https://doi.org/10.5194/egusphere-egu26-14983, 2026.
Keywords: SBAS-InSAR, slope instability,Indian Himalayans, North Vietnam, Sentinel-1, deformation monitoring.
How to cite: Manocha, A. R.: Assessing Slope Stability and Landslide Hazards using InSAR-Based Deformation Monitoring In the India and Vietnam., EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-238, https://doi.org/10.5194/egusphere-egu26-238, 2026.
Active geomorphological processes such as landslides, surface deformation, fluvial erosion, and structural reactivation pose serious geohazards in tectonically and climatically dynamic regions. Accurate identification and monitoring of these processes require high‐resolution surface information capable of capturing spatial variability and short‐term geomorphic changes. In this study, high‐resolution unmanned aerial vehicle (UAV) based optical imagery is used to investigate active geomorphological processes, structural controls, and geohazard distribution in a seismically active region of the northeastern Himalaya of India.
The study is conducted in the Kopili Fault Zone (KFZ), in the Northeast of India. It is a major active tectonic corridor located at the junction of the Himalayan and Indo-Burman plate boundary systems. The region is characterised by steep slopes, intense monsoonal rainfall, dense vegetation, frequent moderate earthquakes, and widespread slope instability. These combined tectonic and climatic conditions result in recurring landslides, rapid landscape modification, and complex interactions between tectonic structures and surface processes.
UAV-derived optical images are processed using photogrammetric techniques to generate high‐resolution orthomosaics and digital surface models. These datasets are used for detailed landslide inventory mapping, identification of scarps, crown cracks, debris accumulation zones, and assessment of landslide geometry and spatial distribution. Structural mapping of lineaments, fault traces, and fracture patterns is carried out through visual interpretation and GIS-based analysis of UAV imagery, enabling evaluation of tectonic controls on slope instability and drainage development.
The results include the generation of a high-resolution landslide inventory, improved delineation of structurally controlled instability zones, and enhanced identification of active deformation and erosion hotspots. The study is expected to demonstrate clear spatial relationships between landslide occurrence, active fault segments, and geomorphic anomalies. Overall, this research highlights the effectiveness of UAV-based optical remote sensing for resolving fine-scale geomorphological processes and improving geohazard characterisation, thereby supporting hazard mitigation, land-use planning, and risk reduction strategies around the Kopili Fault Zone and similar tectonically active regions.
How to cite: Sahu, D. K. and Manocha, A. R.: Investigation of Active Geomorphological Processes and Landslide Mapping Using Advanced UAV Data around the Kopili Fault Zone, in the Northeast Himalayan region of India, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-21553, https://doi.org/10.5194/egusphere-egu26-21553, 2026.
The LAREDAR project addresses transnational flood risk mitigation in the Danube River Basin by focusing on the roles of lakes and reservoirs and by developing tools and guidance to support coordinated management across countries. Led by the Middle Tisza District Water Directorate, LAREDAR operates under the Danube Region Programme priority on climate adaptation and disaster management and is planned for a 30-month implementation period. Its core intent is to strengthen basin-wide cooperation through an integrated platform built on a joint GIS database and improved understanding of transnational flood effects, enabling sustainable and coordinated action during flood events across borders.
The Austrian–Slovenian Mura River is one of three multinational pilot areas selected to characterize the role of lakes and reservoirs in flood mitigation. The Austrian reach is hydrologically modified by hydropower generation, comprising a series of run-of-river power plants with impounded reaches and narrow embankments raised above the adjacent floodplain. During large floods, overtopping of these embankments enables natural floodplain inundation and creates secondary flowing retention that bypasses the power plants. Yet it remains rather unclear how flow regulation and floodplain flow interact.
Previous studies (Volpi et al., 2018; Cipollini et al., 2022; Stecher and Herrnegger, 2022) show that run-of-river power plants typically exert only minor influence on downstream flood peaks. Within the Austrian reach of the Mura Pilot area the focus is on the interdependencies between main channel and floodplain flows in a hydrologically altered river landscape. The lateral exchange between river and floodplain—its controls, dynamics, and consequences for total flood retention at reach to basin scales—remains insufficiently quantified, potentially limiting effective transnational flood management. We adapt the Floodplain Evaluation Matrix - FEM (Habersack and Schober, 2020) to explicitly account for run-of-river power plants and regulated flow regimes to assess the performance of floodplain-impoundment interrelations.
This work aims to (i) quantify retention effects across multiple spatial and temporal scales, (ii) evaluate the effectiveness of past flood mitigation measures, (iii) provide evidence on when and where floodplain connectivity provides meaningful peak reduction, and (iv) clarify upstream–downstream interactions in a transnational setting. The resulting evidence base will extend current knowledge and support river managers in optimizing flood risk mitigation and targeted prevention measures. It will also foster robust transnational cooperation and data exchange for improved flood risk management.
First findings already underline the important retention effect of existing floodplains, but also indicate the potential of optimizing floodplain connectivity, making better use of impounded river reaches for improved flood management. More detailed, quantified results are expected in 2026.
How to cite: Preiml, M. and Bertinotti, J.: Improved transboundary flood risk management through better understanding of floodplain connectivity in an impounded, flow regulated river reach. , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-7999, https://doi.org/10.5194/egusphere-egu26-7999, 2026.
Estimation of flood response in ungauged catchments remains a critical challenge in hydrology, particularly in regions with heterogeneous physiography and limited observational data. In India, the Central Water Commission (CWC) provides regional empirical equations for deriving unit hydrographs within predefined, contiguous hydrological zones. Although widely applied, this zonal framework does not explicitly account for variations in internal catchment structure and drainage network organization. The present study proposes an alternative approach for flood response estimation based on catchment topological characteristics, with application to South Indian catchments located within CWC zones 3d, 3e, 3f, 3g, 3h, and 3i. Initially, unit hydrographs were computed using the CWC regional relationships and subsequently converted into instantaneous unit hydrographs (IUHs). Given the contiguous nature of the selected CWC zones, a topology-based classification of catchments was then introduced to better represent hydrological response mechanisms. Catchments are grouped according to their drainage network configuration, and empirical width functions were derived for each group. Since the width function describes the spatial distribution of contributing areas with respect to flow travel distance, it provides a physically meaningful representation of the instantaneous unit hydrograph of a catchment. A comparative analysis was conducted between IUHs derived from CWC-based unit hydrographs and those obtained directly from width functions. The results show good agreement between the two approaches in terms of hydrograph shape, peak timing, and overall response dynamics, indicating that catchment topology exerts a dominant control on flood response. Based on these findings, new regional relationships were developed using topological classification rather than contiguous geographic zoning. The proposed framework offers a physically based and alternative approach to existing CWC methodologies for estimating ungauged instantaneous unit hydrograph for Indian catchments. By emphasizing drainage network structure over zonal continuity, the approach enhances applicability across catchments with similar topological characteristics and provides a robust tool for regional flood estimation and hydrological modeling in data-scarce regions.
Keywords: Instantaneous Unit Hydrograph, Catchment Topology, Width Function, Regionalization, Ungauged Catchments.
How to cite: Rana, S. and Chavan, S. R.: Proposing an alternative approach based on channel network topology to determine Instantaneous unit hydrographs for ungauged Indian catchments , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-8793, https://doi.org/10.5194/egusphere-egu26-8793, 2026.
Situated in the North Atlantic Ocean, the Azores is an archipelago of nine volcanic islands, where numerous destructive landslide events have occurred over the past five centuries, triggered by several factors, namely seismic activity, volcanic eruptions, and episodes of intense rainfall. Within this context, this study focuses on the Ribeira Quente valley, located in Povoação Municipality (S. Miguel Island), covering an area of 9,15 km². The valley is highly prone to landslides, which often damage the only road to Ribeira Quente village, leaving it isolated. A major event occurred on October 31st,1997, when an episode of very intense rainfall triggered nearly 1,000 shallow landslides, primarily translational slides and debris flows. This event resulted in 29 fatalities, the destruction of 36 houses, and left 114 people homeless, while the village became isolated for over 12 hours.
Three historical landslide inventories were developed for this study. The first inventory, based on a 2004 ortophotomap with a resolution of 40 centimeters and a scale of 1:15,000, included approximately 400 landslides. The second inventory, from 2010, was developed using Google Street View, and contained around 250 landslides. Finally, the third inventory, conducted through fieldwork in 2025, identified approximately 260 landslides. In total, the three inventories include around 910 landslides.
Landslide susceptibility analysis provides the essential basis for hazard mapping, a crucial component for quantitative risk assessment. The main objectives of this study are: (i) to investigate whether there is temporal variability in the spatial distribution of landslide susceptibility results; and (ii) to determine the optimal combination of predisposing factors for inclusion in the landslide susceptibility model, maximizing its predictive performance.
Susceptibility modelling was performed using 11 predisposing factors, which were processed as raster datasets with a 5 m × 5 m resolution, alongside historical landslide inventories. To evaluate the influence of each predisposing factor on landslide distribution, factors were hierarchically ranked by their ability to distinguish between terrain units with and without landslides.
The modeling process employed the Information Value method, a bivariate probabilistic approach derived from Bayesian theory. A total of 2,047 susceptibility models were tested for each landslide inventory, and the best model was selected based on its goodness of fit, determined by computing the Success Rate Curves (SRC) and the Area Under the Curve (AUC). The predictive capacity of the best models was then assessed by computing the Prediction Rate Curves and the corresponding AUC.
This study provides essential tools for land-use planning and civil protection. Landslide susceptibility maps can also support the implementation of site-specific risk mitigation measures and prioritize detailed geotechnical investigations. This research is financially supported by the INTERREG program through the PRISMAC project – “Análise, Mitigação e Gestão do Risco de Movimentos de Vertente Potenciados pelas Alterações Climáticas na Macaronésia” (Ref. 1/MAC/2/2.4/0112).
How to cite: Silva, M. J., Marques, R., Silva, R. F., Andrade, C., and Amaral, P.: Assessing Temporal Consistency and the Effect of Predisposing Factors in Landslide Susceptibility Models in the Ribeira Quente Valley (São Miguel Island, Azores), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-13400, https://doi.org/10.5194/egusphere-egu26-13400, 2026.
The precise monitoring of landslide deformation is essential to understand slope dynamics and its stability condition in mountainous terrain. It affects transportation, communication, and waterways directly, and associated damages hinder economic growth in the region. The study presents a comparative assessment of surface deformation at the Prashar landslide site (Himachal Pradesh) using high-resolution unmanned aerial vehicle (UAV) photogrammetry and satellite-based Interferometric Synthetic Aperture Radar (InSAR). Drone-based surveys were conducted in two time frames (April 2024 and March 2025) to obtain high-resolution Digital Surface Models (DSMs). Sentinel-1 C-band images (from May 2023 to November 2024) were used for getting time-series deformation using EZ-InSAR and MintPy workflows. Results from both methods revealed consistent results signifying that the landslide site is deforming at a creeping rate. Rate of deformation from DSM differencing revealed surface deformation ranging from -55 cm to +46 cm over 13 months. The zone of erosion is concentrated along the crown portion of the landslide, accumulating debris along the body of the landslide. InSAR results showed mean line-of-sight deformation values between -3.35 and +4.68 cm/year, with the highest subsidence concentrated at the crown portion, however additional deformation was detected on the opposite valley flank. Despite differences in spatial resolution, both techniques consistently identify the same active deformation zones with a comparable deformation rate of approximately 8 cm per month when temporal averaging is considered. UAV-based DSMs provide centimeter-scale details of crack propagation, displacement, and associated local geomorphic changes. On the other hand, InSAR captures continuous regional-scale deformation trends, particularly effective over sparsely vegetated areas. The close agreement between UAV and InSAR-derived deformation patterns demonstrates the robustness of integrating high-resolution drones with satellite-based time-series analysis. This multi-sensor approach enhances the reliability of landslide monitoring in rugged terrain and offers a practical framework for long-term hazard assessment and early warning applications.
Keywords: UAV differencing, InSAR deformation, high-resolution DSM, Landslide monitoring, Prashar landslide site.
How to cite: Dhiman, N., Singh, A., Mahanta, K. K., Pathak, B., and Shukla, D. P.: Comparative Assessment of Landslide Deformation Using UAV-derived DSM differencing and InSAR: A Case Study from the Prashar Landslide site, Himachal Pradesh, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-16532, https://doi.org/10.5194/egusphere-egu26-16532, 2026.
For an effective landslide hazard assessment, it is essential to accurately predict the occurrence, timing, and magnitude of landslides. This work presents a detailed analysis of landslide spatiotemporal probability and size distribution for a case study Vietnam. Spatial probability was modeled using Extreme Gradient Boosting (XGB), Random Forest (RF), and Logistic Regression (LR) with 12 predictor variables and a landslide inventory recorded from 2017 to 2024. Temporal probability was estimated using daily rainfall data, applying an event rainfall–duration threshold in combination with a Poisson model. Landslide size probabilities were derived from a probability density function (PDF). Finally, a set of hazard maps was produced for three different time periods and three landslide size classes.
The study has been supported by the Polish National Science Centre (project no 2023/49/B/ST10/02879).
How to cite: Trung Hieu, T., Pawlik, Ł., Van Tien, P., and Cong Quan, N.: Machine learning and rainfall threshold-based assessment of landslide hazards in Vietnam, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-17324, https://doi.org/10.5194/egusphere-egu26-17324, 2026.
Landslide size is a strong predictor of runout distance across a wide range of landslide types and therefore represents a key parameter for hazard assessment. Within the conceptual risk framework, landslide hazard analysis requires estimating the probability of exceedance of landslide magnitude, in a manner analogous to approaches commonly applied to other natural hazards, such as earthquakes. Integrating magnitude–probability relationships into landslide hazard assessments enhances the robustness of potential impact characterization and supports informed risk-based decision-making.
Situated in the North Atlantic, the Azores archipelago comprises nine volcanic islands where numerous destructive landslide events have occurred over the past five centuries, triggered by seismic activity, volcanic eruptions, and intense rainfall. Within this context, this study focuses on the Ribeira Quente valley (Povoação Municipality, São Miguel Island), covering 9.15 km². The study area exhibits high susceptibility to landslide occurrence, characterized by very friable volcanic deposits and extremely steep slopes. Landslides frequently affect the only access road to Ribeira Quente village, leaving it isolated. Since 1900, 31 landslides events have affected Ribeira Quente parish, causing 32 fatalities. A major event on 31 October 1997 triggered nearly 1,000 shallow landslides, resulting in 29 fatalities, the destruction of 36 houses, and 114 people left homeless, while the village remained isolated for over 12 hours.
Three historical landslide inventories were compiled. The first inventory, based on 2004 data, included ~400 landslides. The second, from 2010, contained ~250 landslides. The third, compiled in 2025, identified ~260 landslides. Overall, the inventories include approximately910 landslides, mainly superficial translational slides and debris flows.
The main objective of this study is to propose and parameterize probability distributions specifically tailored to the study area. The landslide scar areas were used as the magnitude descriptor. A total of 65 theoretical probability distributions were fitted to the scar area data. Parameterization was performed using the maximum likelihood method, and goodness of fit was evaluated with the Kolmogorov–Smirnov (K-S) test. The best-fitting probability density function (PDF) was then selected, and exceedance probabilities for different magnitude scenarios were computed based on its complementary cumulative distribution function (1 − CDF).
This study provides a probabilistic approach for assessing landslide magnitudes, presenting valuable insights for land-use planning and civil protection. The derived magnitude–exceedance functions enhance hazard characterization and can guide the prioritization of risk mitigation actions and targeted geotechnical investigations. This research was supported by the INTERREG program through the PRISMAC project – “Análise, Mitigação e Gestão do Risco de Movimentos de Vertente Potenciados pelas Alterações Climáticas na Macaronésia” (Ref. 1/MAC/2/2.4/0112).
How to cite: Marques, R., Silva, M. J., and Silva, R. F.: Landslide Magnitude Exceedance Probability Modelling for Ribeira Quente Valley (São Miguel Island, Azores-Portugal), EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-19736, https://doi.org/10.5194/egusphere-egu26-19736, 2026.
Extreme flood events naturally act as drivers of geomorphic heterogeneity, creating complex channel-floodplain systems characterized by diverse bedforms, bank erosion features, and sediment splays. However, the subsequent phase of flood recovery often involves rapid and extensive anthropogenic interventions that counteract these natural processes. This study evaluates the loss of geomorphological diversity in montane streams of the Opava River Basin (Czechia) by analyzing the conflict between natural recovery and technical river management.
The research methodology employs a multi-temporal approach combining field investigation and remote sensing. While systematic geomorphological field mapping was conducted at two key stages—immediately following the 2024 flood to record the "pristine" impact and one year later to assess the final state—UAV photogrammetric campaigns were executed repeatedly throughout the post-flood year. This high-frequency monitoring provided multiple temporal windows, allowing us to track the precise sequence of changes and distinguish between gradual natural adjustments and abrupt anthropogenic modifications.
The analysis of this time-series data reveals a significant trajectory of channel simplification:
- Erasure of Complexity: The repeated UAV models document how initial flood-created features (cut banks, gravel bars) were systematically removed by engineering works. In reaches subjected to heavy machinery, geomorphic diversity was reduced by up to 100%.
- Dynamics of Intervention: The multiple time windows highlighted that the most severe loss of diversity often occurred weeks or months after the flood event itself, during the "recovery" phase. Moreover, this loss of diversity was significantly stronger in proximity to habited areas compared to natural river reaches.
- Impact of Intensity: We identified a direct correlation between the intensity of technical adjustments and the degree of channel homogenization. While "soft" interventions allowed for the partial preservation of flood-induced forms, heavy engineering works resulted in the complete artificial straightening of the thalweg.
The study demonstrates that high-resolution UAV monitoring is essential for capturing the transient states of river recovery. The findings suggest that current post-flood protocols often prioritize rapid hydraulic streamlining at the expense of ecological integrity, effectively "resetting" the river's geomorphic value to a pre-flood, or even simpler, state.
How to cite: Lehký, M. and Langhammer, J.: Geomorphic Diversity Loss Following Post-Flood Interventions, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-11066, https://doi.org/10.5194/egusphere-egu26-11066, 2026.
Posters virtual: Tue, 5 May, 14:00–18:00 | vPoster spot 3
EGU26-5929 | ECS | Posters virtual | VPS26
Controls on the size and mobility of deep-seated landslides in the North Tanganyika - Kivu Rift region, AfricaTue, 05 May, 14:03–14:06 (CEST) vPoster spot 3
The size and mobility of landslides control their impact on both landscapes and communities. Despite their importance to understanding landslide mechanisms and associated hazards, few studies have examined the factors controlling these two characteristics, particularly at a large scale. This is especially the case for deep-seated landslides that occur across diverse geomorphological and lithological settings. Further, most research focuses on recent landslides and thus fail to consider historical processes that could be associated with environmental conditions that differ from the contemporary ones. Here, we investigate the influence of geomorphology and lithology on the size and mobility of old and recent deep-seated landslides in the North Tanganyika-Kivu Rift region in Africa, an under-researched mountainous environment located in the tropics. Based on a comprehensive inventory of ~2500 landslides, we show that mobility increases with size, especially for the old landslides. These old landslides are significantly larger than the recent ones, likely due to potential progressive landslide growth over time and influenced by the region’s paleoseismic activity. The main controls on both the size and mobility of deep-seated landslides are lithology and, to a lesser extent, fluctuations in Lake Kivu’s level during the Holocene. Landscape rejuvenation by migrating knickpoints associated with rifting also plays a key role in determining landslide size: in rejuvenated landscapes, landslides tend to be larger than those in relict landscapes. The presence of these large landslides favours the development of smaller ones along their margins, reflecting the influence of path dependency on landslide occurrence and size. Our findings underscore the importance of considering the chronology of landslide occurrence and the long-term legacy of landscape evolution in shaping landslide characteristics.
How to cite: Mugaruka Bibentyo, T., Dille, A., Deijns, A., Nzolang, C., Dewaele, S., and Dewitte, O.: Controls on the size and mobility of deep-seated landslides in the North Tanganyika - Kivu Rift region, Africa, EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-5929, https://doi.org/10.5194/egusphere-egu26-5929, 2026.
EGU26-570 | ECS | Posters virtual | VPS26
Geomorphic controls on flood response using the Width Function Instantaneous Unit Hydrograph frameworkTue, 05 May, 14:45–14:48 (CEST) vPoster spot 3
The hydrological response of a basin is fundamentally controlled by geomorphic processes, structures, and physiographic characteristics. Horton’s geomorphological laws, basin topology, and kinematic properties have long been employed to derive flood response in ungauged basins through various Geomorphological Instantaneous Unit Hydrograph (GIUH) frameworks. This study investigates ten ungauged tributary sub-basins of the Shilabati River in eastern India to analyse how basin morphometry and topology regulate travel-time distribution of water particles and flash-flood potential. The Width Function Instantaneous Unit Hydrograph (WFIUH), a GIUH variant, is applied to derive the geomorphological control on peak flow and time to peak, while the morphometric analysis is performed to investigate the effect of basin characteristics on these hydrologic response parameters. The WFIUH is obtained using the flow length extracted from the SRTM DEM, together with spatially variable and fixed hillslope velocities estimated from land use-land cover and slope using the Soil Conservation Services (SCS), uniform-flow, and Manning’s velocity formulae. Due to the absence of observed streamflow, WFIUH results are evaluated against the Geomorpho-climatic Instantaneous Unit Hydrograph (GcIUH) derived from climate-dependent channel velocity and drainage network topology, as well as observed flood events.
Results show that all variable-velocity WFIUHs have longer time bases and a lower peak flow than fixed-velocity WFIUHs, because the highest velocity cells are associated with the smallest drainage contributing areas. The SCS-based variable velocity WFIUH aligns with the GcIUH, reproducing both the peak flow and time to peak of the IUH more accurately compared to the other methods. Small, circular, and comparatively steeper sub-basins exhibit shorter times to peak (8.5-10.5 hours), indicating a high flash-flood potential, mainly in sub-basins 3-6. On the contrary, elongated and well-bifurcated sub-basins reveal slightly delayed peaks (10.5-15.5 h) but remain capable of producing moderate-to-high floods due to their larger drainage areas, as confirmed by the flash flood event in 2025 in sub-basins 1, 8-10. Correlation analysis reveals that circularity ratio, relief ratio, and hypsometric integral are positively associated with peak flow, suggesting enhanced flow synchronization in compact and steep sub-basins. In contrast, time to peak shows moderate to strong negative correlations with these parameters and positive correlations with stream length and bifurcation ratios, indicating delayed response in elongated and highly branched drainage networks due to dispersed flow paths.
Therefore, basin morphometry and drainage network topology effectively govern hydrologic responses of the sub-basins. The spatially variable SCS velocity-based WFIUH provides a more realistic depiction of hydrologic response in ungauged sub-basins. Hence, this method is well-suited for event-based lumped hydrological modelling as well as for sub-basin prioritization in flash flood risk assessment.
How to cite: Das, T. and Das, S.: Geomorphic controls on flood response using the Width Function Instantaneous Unit Hydrograph framework , EGU General Assembly 2026, Vienna, Austria, 3–8 May 2026, EGU26-570, https://doi.org/10.5194/egusphere-egu26-570, 2026.
