Cascading hazards come into focus of hazard and risk research in the last 15 years and is strongly connected to studies on multi-hazards and compound hazards. Unexpected cascading events and related casualties and losses of properties draw the attention to consider the possible amplified risks induced by cascading hazards.

The contribution will focus in the first part on key concepts in relation to cascading hazards and will address briefly the challenges which may occur due to the general terminological ambiguity because the term cascading hazards tends to be used interchangeably with multi-hazards, cascading events, cascading disasters, or compound hazards or events. The main focus is on the analyses of different types of interactions which may occur during a cascading hazard events and their dependency on time and space. In the second part, the main question addresses the influence of climate and environmental change on cascading hazards including the occurrence of cascading hazards, changes of types of cascading hazards or interactions within the cascading hazard event. Current challenges regarding the approaches used to analyse and better understand cascading hazards are presented as well as first ideas to answer the questions what is missing, what is needed and how it can be used for hazard and risk analysis/management. 

How to cite: Keiler, M.: Cascading Hazards – the challenges to understand interactions, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16937, https://doi.org/10.5194/egusphere-egu24-16937, 2024.

The intense melting of glacial ice and permafrost can increase the presence of temporarily stored liquid water in dynamic high-alpine environments. A sudden release of this water, especially in volcanic settings, might trigger a process chain of severe consequences. During a period of increased periglacial degradation between 2015 and 2017, several large-volume (> 6.0 × 10⁵ m³), outburst-related secondary lahars damaged local infrastructure on the populated southeastern slopes of Chimborazo volcano in Ecuador. The insufficient understanding of secondary lahars associated with the sudden outburst of water complicates the identification of initiating processes and hinders the ability to decipher the governing mechanisms involved during propagation.

In this study, we present how we (1) identified initiation mechanisms of past secondary lahars at Chimborazo, (2) numerically back-calculated these events, (3) developed future lahar scenarios, and (4) quantified their impact on the local population. We performed a retrospective calibration approach to simulate a secondary lahar using the physics-based model RAMMS::Debris Flow. By introducing a novel two-stage outburst scenario development concept, we were able to predict potential future lahars. Finally, applying a standards-based verification of the structural components of residential development allowed us to evaluate the physical impact of potential lahars on infrastructure. We also assessed how increasing the wall thickness affects high- and low-risk areas.

Our results show that the observed secondary lahars can be numerically reproduced with a set of frictional parameters of µ = 0.028 (Coulomb-type friction) and ξ = 600 ms^-2 (turbulent friction). The model shows high agreement with locally obtained data (Vasconez et al., 2021) on total lahar volume, flow distance, discharge, and flooded area (deviation from target value = 20 %). By comparing the climatic and topographical situation of similar events at other study sites with the conditions at Chimborazo, we assume that glacial/periglacial destabilization processes may have accompanied the initiation of past lahars. Through deciphering the past initiation processes, our scenarios resulted in volumes between 2.7 × 10⁵ m³ (high probability) and 10.8 × 10⁵ m³ (very low probability) for a climatically derived reference period of 180 years. The structural validation of the component resistance identified high risk for approximately 24 % of the entire runout area. The adjustment to 11 cm wider bricks reduces this area by 5 %.

Only a precise quantification of the ice content and dynamic behavior within the source region enable to estimate the influence of destabilization processes on lahar initiation. However, this work makes an important contribution to supporting informed decision-making in land use planning by implementing an interdisciplinary methodology for analyzing the impacts of mass movements.

In this study, we showed that a retrospectively calibrated numerical model enables the simulation of future outburst-triggered lahars, and we further provided a quantification of their impact on downstream communities.

Vasconez, F.J., Maisincho, L., Andrade, S.D., Cáceres Correa, B.E., Bernard, B., Argoti, C., Telenchana, E., Almeida, M., Almeida, S. & Lema, V. (2021): Secondary Lahars Triggered by Periglacial Melting at Chimborazo Volcano, Ecuador. – Revista Politécnica, 48: 19–30.https://doi.org/10.33333/rp.vol48n1.02

How to cite: Mühlbauer, S., Frimberger, T., and Krautblatter, M.: Secondary Lahars Impacting on Building Structures at Chimborazo Volcano: A Retrospective and Scenario-Based Modeling Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13482, https://doi.org/10.5194/egusphere-egu24-13482, 2024.

The global climate is changing, and the effects of these changes on natural hazards are increasingly being felt, particularly by the populations in low- and middle-income countries. Consequently, in the last decades, there has been much research examining the extent of these effects, but the focus has largely been on hydrometeorological hazards. The potential effects of climate change on geological hazards, like earthquakes and volcanic activity, is less studied and deserves greater attention.

Amplified Risk is a four-year program currently being led by the GeoHazards International (GHI), a non-profit committed to saving lives by empowering at-risk communities worldwide to build resilience ahead of disasters and climate impacts. Funded by the United States Agency for International Development (USAID), the overarching goal of the program is to increase collective understanding of how volcanic and earthquake hazards and their societal impacts may be affected by climate change in at-risk low- and middle-income countries.

In line with this, we have thus far explored through literature review and subject matter expert consultations how climate change may alter earthquake and volcanic processes and associated hazards, considering eight climate change signals as the starting point: increased precipitation, decreased precipitation, increased temperature, increased rain-drought cycles, increased free-thaw cycles, increased typhoons, increased wind and sea level rise. Our results show the potential amplifying, cascading, and compounding effects of climate change on geological hazards.   

In general, climate change can affect earthquake and volcanic hazards in two ways: Firstly, it can directly trigger or contribute to directly triggering the hazards as a result of stress regime change following climate-induced variations of loads on the earth surface, mainly due to changes in the volume of ice and water, e.g., glacier melting. Secondly, climate change prepares the ground so that the occurrence of secondary hazards becomes more likely should an earthquake or volcanic eruption occur. For instance, increased precipitation increases soil saturation, making liquefaction more likely in the event of an earthquake.     

In this presentation, we discuss the findings to date in more detail. We also present the flowchart that summarizes our result, which we intend to publish online as an interactive informational tool that may be useful to risk managers, authorities, community leaders, and researchers in appraising the range of effects from climate change on local hazards, and therefore in determining and prioritizing intervention measures.

How to cite: Beroya-Eitner, M. A., Stenner, H., Bowman, L., and Nelson, K.: Amplified Risk: How Climate Change is Modifying the Risks from Geological Hazards, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10776, https://doi.org/10.5194/egusphere-egu24-10776, 2024.

Sediment cascades are a convenient way of conceptualizing the transfer of sediment from hillslope production areas, through the river network, to the river basin outlet. Distributed hydrology-sediment models play an important role in the prediction of these source-to-sink links, because they can explicitly connect water and sediment fluxes along topographically-driven pathways. Here, we provide some examples of such cascade-based hydrology-sediment model applications in alpine environments and some problems related to their use.

In particular, we highlight two critical problems with hydrology-sediment modelling that go beyond trivial model calibration difficulties. These address fundamental issues of (a) non-uniqueness in sediment source mixing, and (b) sediment supply limitations. The first problem of non-uniqueness is known in hydrological modelling as the curse when models perform well at basin outlets for the wrong reasons, misrepresenting hydrological processes within the basin. In geomorphology, this concept has not received the same level of attention. Here we show that even a calibrated physically-distributed hydrology-sediment model can be subject to non-uniqueness, and provide the same suspended sediment yields at the basin outlet with completely different combinations of sediment sources. Including sediment tracers in model validation helps to identify this problem, and it is also helpful to check simulations at sub-basin scales where we are closer to distinct sediment sources. The second problem of sediment supply limitations is a challenge for all models that rely on transport capacity formulas for sediment transport. In our experience, both supply and transport capacity limit sediment transport at the basin scale, and we need to include this in our models. For example, we show that supply limitations can completely change the seasonality of sediment yields and render many climate change impact studies worthless.

Finally, we argue that both problems above, at least for suspended load, can be partially addressed by novel monitoring. For example by low cost smart sensors that allow a distributed sensing of sediment fluxes above and below potential sediment sources at high resolutions, or by high resolution remote sensing to capture space-time variability in river turbidity. This kind of data can dramatically improve our ability to calibrate models, reduce non-uniqueness, and over the long term identify the key signatures of sediment supply in river systems. It is our opinion that improving the predictions of climate and environmental change effects on sediment yields requires both better model validation as well as new data.

How to cite: Molnar, P., Meierhans, S., Battista, G., Hirschberg, J., Droujko, J., and Sinclair, S.: Non-uniqueness in sediment transport in river network hydrology-sediment modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19175, https://doi.org/10.5194/egusphere-egu24-19175, 2024.

Debris flow is an important process that shapes steep landscapes, connecting the hillslopes and fluvial domains. Yet, it is unclear how debris flows quantitatively influence the topography. Here, we propose and develop a new framework considering debris flows as stochastic processes in long-term landscape evolution. We assume that debris flows occur randomly in time with different initial debris flow volumes, which we model using five different distribution functions. Debris flows propagate along the channel and increase their volume by eroding additional material using deterministic equations. The model predicts the slope-area relationship that is generally assumed to be indicative of debris-flow-dominated landscapes. We suggest a new equation to fit the slope-area relationship, including both debris flow and fluvial domains. This equation features a total of five metrics, two of which are power law exponents, two are representative areas, and one representative slope. The topography in the debris flow-dominated domain is sensitive to the properties of the debris flow, e.g., the initial volume of debris flow, frequency, erosion coefficient, Manning coefficient, uplift rate, and channel width and length. The representative slope and area are primarily sensitive to the total initial volumes of the debris flow, and secondarily to the frequency of occurrence of debris flows. The type and shape parameters of distributions and the debris flows’ volume and frequency have limited effects on the slope-area relationship.

How to cite: Liu, D., Tang, H., Braun, J., and Turowski, J.: A stochastic landscape evolution model framework for debris flow and fluvial processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10204, https://doi.org/10.5194/egusphere-egu24-10204, 2024.

Landslides and torrential flows are among the most dangerous processes that occur on hillslopes, and they are mostly triggered by intense rainfall events. These phenomena are not only hazardous in themselves, but they can also have a more significant impact downstream when they interact with channels or the river network. When multiple landslides are simultaneously triggered by a rainfall event that affects an extensive area, they can initiate chains of further hazards due to the sudden and massive influx of sediment they bring onto channels and rivers. Therefore, it is crucial to study the connectivity between slopes and the river network to evaluate areas with a potentially higher sediment contribution to the river network. Ultimately, this information will help to assess flood hazards and mitigate risks, as well as assist in the planning of protective structures, drainage works, and other relevant measures.

We conducted a study on the slopes of the Tordera River basin (NE Spain). This river flows from the Montseny (Catalan Coastal range)  into the Mediterranean Sea. The study area was affected by a regional landslide event that occurred in January 2020 during the Gloria Storm (more than 480 mm of rainfall was measured in 96 hours in the region). We employed the index of connectivity, which is based on Borselli et al. (2008), to examine the connectivity between the slopes and the river network. The outcomes of this analysis were subsequently compared to a landslide inventory (more than 1000 mass movements) to determine whether the high amount of sediment present in the lowlands could have originated from landslides in the upper part of the basin.

According to the results of this study, slopes with high connectivity experienced a high density of landslides. The sediment that flowed down the slopes and reached the rivers added to the flood that occurred downstream. This flood carried a considerable amount of sediment which caused the widening of the active channel and the growth of the Tordera delta. The impacts of the Gloria storm on the infrastructure caused significant economic losses.

Borselli, L.;  Cassi, P.;  Torri, D. Prolegomena to sediment and flow connectivity in the landscape: A GIS and field numerical assessment, CATENA, Volume 75, Issue 3, 2008, Pages 268-277, ISSN 0341-8162, https://doi.org/10.1016/j.catena.2008.07.006.

How to cite: Abancó, C., Guinau, M., González, M., Pinyol, J., and Palau, R. M.: Assessing slope-river connectivity for evaluating cascading landslide hazards: A case study of Tordera river basin, NE Spain., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15047, https://doi.org/10.5194/egusphere-egu24-15047, 2024.

Large wood (LW), defined as woody pieces exceeding 1 m in length and 10 cm in diameter, significantly shapes channel morphology and ecological habitats within Alpine torrents. Lower-order alpine torrents, with their smaller drainage areas and steeper gradients, are particularly sensitive to LW dynamics. The movement of LW greatly affects channel processes, altering flow patterns and sediment dynamics. LW can retain sediments and form log steps that may reduce bed erosion. Moreover, the accumulation of LW at bridge piers and filters or openings of retention check dams can exacerbate flood hazards, emphasizing the crucial need for its accurate quantification for more effective hazard assessments and protection measure design. Our investigation aims to assess changes in the LW budget in the Ru de Vallaccia catchment (covering 1.72 km², Melton number 0.97, mean channel slope 45%) in the province of Belluno, Veneto, Italy. Specifically, we explore variations in LW volume before and after a heavy rainstorm event with a return period between 2 and 5 years that occurred between the 30^th of October and the 2^nd of November 2023. Furthermore, this study examines the correlation between segments of the channel affected by sediment erosion and deposition and changes in both the spatial distribution and volume of LW within the channel. Field surveys coupled with high-resolution topography (HRT) assessments conducted before and after the rainstorm event (July and November 2023) allow for a comprehensive evaluation of sediment and LW budgets. Our methodology involves direct field measurements of LW and photointerpretation using GIS software on orthophotomosaics resulting from HRT surveys. Additionally, we utilize the Digital Elevation Model (DEM) obtained from HRT surveys to analyze channel geomorphological changes through the DEM of Differences (DoD) technique, enabling precise quantification and visualization of sediment alterations related to erosion and deposition phenomena. Preliminary findings reveal pronounced sediment mobility, significant alterations in channel morphology, and notable changes in both the spatial distribution and volume of LW. The results of the study highlight the close link between patterns of erosional or depositional sediment dynamics and alterations in the LW budget, elucidating the intricate interaction between geomorphic processes and the presence and evolution of LW during subsequent flood events in steep mountain basins. In addition, these insights have substantial implications for addressing or guiding periodic monitoring of LW and thereby improving our hazard mitigation strategies against those sediment transport events (bedload, debris flood, and debris flow) capable of encompassing significant amounts of LW.

How to cite: Martini, M., Bettella, F., and D'Agostino, V.: Interaction Between Large Wood and Sediment Transport in an Alpine Torrent in the Dolomites, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10429, https://doi.org/10.5194/egusphere-egu24-10429, 2024.

Over the past decades, cascading hazards that include landslides, debris flows, and floods have caused several major disasters in tropical mountain regions. Even though such cascading hazards also occur in steep terrain elsewhere, some natural drivers such as very high humidity with associated heavy rainfalls, and deeply weathered soil profiles, may amplify the reach and impacts of these cascades in tropical mountains. There, torrential fans sustaining dense settlements are especially prone to rainfall-triggered hazard cascades but remain largely understudied compared to temperate mountain regions. Challenges in their hazard assessment include a lack of consensus regarding the scientific terminology to describe, analyse, and record these events; and their complexity, given that, combining traditional single hazard assessment fails to capture the amplification of the damages. On the other hand, their occurrence in remote, undeveloped regions where they are poorly or not documented, and their low temporal recurrence, decreases hazard awareness and increases the growth of urban settlements in exposed areas.

The goal of this study is to review widespread cascading torrential hazards in the tropics as a common and destructive interaction of mass-wasting and flow processes. The study has two different steps: the first is a review of existing terminology concerning regional hydrometeorological cascading hazards in different latitudes and environments, as an attempt to clarify the existing gaps and differences in information between tropical and higher latitude areas. The second step is the description of the main morphological and triggering characteristics of such events. For this, we compiled a dozen regional cascading torrential events that occurred between 2017 and 2023 in different tropical regions of the American, Asian, and African continents, caused by different triggering mechanisms, including extreme rainfall and earthquakes, or both. Using high-resolution satellite images, the events were mapped differentiating the extent of landslide initiation, debris flows runout, and floodings. Additionally, we used freely available remote sensing sources to extract information concerning the geomorphology, soil texture, and triggering rainfall of each study area. Using different statistical tools, we analysed the relationship between different morphological features, triggering rainfall and soil texture, to distinguish the main characteristics of such events in both the basin and the sub-process scale.

As preliminary results of this ongoing research, we have found an important gap in information concerning widespread cascading torrential hazards in tropical regions. Furthermore, the analysis of our inventory allowed us to identify key factors that contribute to the triggering, propagation, and connection of hazards, including the very high availability of coarse-textured soils and higher sediment connectivity within affected catchments. Furthermore, we found that the spatial connection of the sub-processes involved in these events (landslides, debris flows, and floods), is given by their overlap within the different process domains of basins.

This initial approach provides a preliminary understanding of the conditions that promote cascading torrential hazards in tropical regions, which can aid in developing more accurate hazard assessment tools and implementing effective strategies to mitigate risks in the tropics, considering its unique multi-hazard and complex setting.

How to cite: Arango, M. I., Hürlimann, M., Aristizábal, E., and Korup, O.: Widespread cascading torrential hazards in tropical regions , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14250, https://doi.org/10.5194/egusphere-egu24-14250, 2024.

Torrential risk protection works have a long tradition in the Alps, where these measures have allowed more intensive use of the landscape since the twentieth century and form the basis for rational management of the risk of torrential floods. While the maintenance and management of protective works makes it possible to control their inevitable deterioration and to extend their life, the collapse of these systems should be always considered in the frame of the residual risk management. This work aims to i) analyse the catastrophic debris flow occurred on October 2018 in the Rotian river basin (Eastern Italian Alps) during which a series of check dams collapsed magnifying the event and causing a casualty and severe damages, and ii) to identify implications for hazard monitoring and management. The work is based on post-event investigations, witness accounts, remote sensing information and local station data, hydrogeomorphic data and models, and systematically analyses the geo-environment, climate conditions and check dam structural conditions which characterized the geohazard cascade of events. In particular, results from the application of a couple hydrological and hydraulic model for the triggering and propagation of the debris flows event are used to inform the analysis. The results from this work are exploited to inform a discussion about the future of these works, which concerns not only the structural and maintenance aspects of the single work, but also involves the risk management requests of the systems of works which in recent decades have evolved significantly.

How to cite: Marchi, L., Borga, M., Zugliani, D., and Rosatti, G.: Geohazard cascade and mechanism of large debris flows in the Rotian river basin (NE Italy): implications to hazard monitoring and management, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21166, https://doi.org/10.5194/egusphere-egu24-21166, 2024.

Debris-flow activity is expected to change in the future following the expected changes in sub-daily rainfall rates. In this study, we connect high-resolution climate simulations from an ensemble of recently developed convection-permitting models (CPM) and a threshold-based precipitation model for debris-flows triggering. We are considering CPM runs over historical (1996-2005), near future (2041-2050) and far future (2090-2099) decade-long periods. Given the biases affecting the CPM simulations and the desire to avoid bias-correction procedures, which may introduce distortions into the precipitation simulations, we propose a methodology to map the debris-flow threshold into the simulated climates. This is obtained by evaluating the return levels of the threshold precipitation rates at different durations, and mapping these in the climate simulations using the same return levels. The Simplified Metastatistical Extreme Value (SMEV) methodology is exploited for the precipitation statistical analysis. The suitability of the proposed framework is tested on the Moscardo catchment, a small study basin located in the eastern Italian Alps, where the debris flow activity is mainly transport-limited. This case study is particularly remarkable due to the high frequency of debris flows and a monitoring system working since 1990, which has permitted establishing reliable rainfall . The debris-flow triggering precipitation events are assessed by considering changes in their frequency, depth and seasonality. The promising preliminary results support the use of this approach to assess debris flow hazards in a changing climate.

How to cite: Menapace, A., Dallan, E., Marra, F., Marchi, L., Larcher, M., and Borga, M.: How is climate change affecting hydro-meteorological triggering for debris flows? An assessment based on convection-permitting models and a bias-neutral procedure, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5386, https://doi.org/10.5194/egusphere-egu24-5386, 2024.

The Himalayas are increasingly vulnerable to the impacts of climate change, with recent years experiencing a surge in the frequency of natural hazards. The risk escalates when events unfold in a cascading manner, where a primary hazard triggers a secondary one. Therefore, it is crucial to develop an integrated framework to assess the ramifications of these cascading hazards. This framework plays a pivotal role in providing early warnings, considering the uncertainty introduced by rainfall input. The presented framework simulates the dynamic interplay between intense precipitation events and hill slopes, potentially triggering landslides. It subsequently models the debris flow resulting from the runoff formed by precipitation mixing with landslide deposits, culminating in debris runout. To address data uncertainties, the framework integrates four diverse precipitation data sources: gridded observation datasets, reanalysis data, satellite data, and numerical weather prediction models. The methodology assesses sediment volume originating from hillslopes and anticipates the sediment volume reaching river junctions during extreme events. Additionally, it involves the numerical simulation of the initial stages of the cascading nature of geohazards, specifically the transformation of landslides into debris flows. The framework's validation is conducted using the 2013 North India Floods, an extreme precipitation event that triggered over 6000 landslides and debris flows.

How to cite: Dixit, S., Subramanian, S. S., and Sen, S.: Exploring Uncertainties Within a Framework for Assessing Extreme Precipitation-Induced Cascading Hazards in the Himalayas , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1049, https://doi.org/10.5194/egusphere-egu24-1049, 2024.

Rainfall characteristics such as intensity, duration, and frequency are key determinants of the hydro-geomorphological response of a catchment. The presence of non-linear and threshold effects makes the relationship between rainfall variability and geomorphological dynamics difficult to quantify. This is particularly relevant under predicted exacerbated erosion induced by an intensification of hydroclimatic extremes. In this study, we quantify the effects of changes in rainfall temporal variability on catchment morphology and sediment erosion, transport, and deposition across a broad spectrum of grain size distributions and climatic conditions. To this purpose, multiple rainfall realizations are simulated using a numerical rainfall generator, while geomorphic response and soil erosion dynamics are assessed through a landscape evolution model (CAESAR-Lisflood). Virtual catchments are used for the numerical experiments and simulations are conducted over centennial time scales. Simulation results show that higher rainfall temporal variability increases net sediment discharge, domain erosion and deposition volumes, and secondary channel development. Particularly, dry regions respond more actively to rainfall variations and finer grain size configurations amplify the hydro-geomorphological response. We find that changes in erosion rates due to rainfall variations can be expressed as a power-law function of the ratio of rainfall temporal variabilities (quantified here through the Gini index). Results are further supported by long-term observational data and simulations over real catchments. Such quantification of the effects of predicted changes in rainfall patterns on catchment hydro-geomorphic response, as mediated by local soil properties, is crucial to forecasting modifications in sediment dynamics due to climate change.

How to cite: Lian, T., Peleg, N., and Bonetti, S.: Quantifying the effects of rainfall temporal variability on landscape evolution processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5581, https://doi.org/10.5194/egusphere-egu24-5581, 2024.

Devoting more efforts to understand how arid landscapes respond to extreme rainfall events, given the expected increase in storm frequency in the future due to global warming projections, is of great relevance and therefore needs to be addressed. While local studies of recent storm impacts in drylands have proven to be useful, our understanding of global impacts at local-and-regional-scales over longer time-scales is now more qualitative than quantitative.

Deciphering the effects of erosion runoff processes operating during extreme rainstorm events requires developing practical measuring approaches that assist understanding the temporal and spatial extent of erosion and sediment pathways in the ephemeral drainage networks of bare lands. The advent of Synthetic Aperture Radar (SAR) satellite missions with, for example, the Sentinel 1 constellation from the ESA, has provided a great number of images that can be used to map the areal and temporal extent of erosion during rainstorm events. As a result, we are now able to unravel surface runoff erosion operating in arid areas using InSAR coherence change detection following, for example, the work of Cabré et al. (2020, 2023). Interferometric SAR (InSAR) coherence can be used to decipher the sediment entrainment areas and identify channels and drainages disturbed by the passage of floods. However, the coherence remains a dimensionless parameter with no physical meaning of surface change. Thus, it cannot be used yet to estimate surface change processes in an automatic basis. For this reason, we have explored the areas with surface change identified in InSAR coherence images using SAR amplitude and field calibration data. In the identified surface change areas we have performed grain-size measurements to prove that sediment grain-size diameter (e.g., D84, D50) in ephemeral channels is well correlated (R=0.93 and 0.72, respectively) with SAR amplitude values and therefore can be used to (i) unravel the downstream variations in grain-size by providing valley-floor grain-size maps and, (ii) identify fluvial features (e.g., longitudinal bars) preserved within the ephemeral channels after the passage of a flood. The latter can be of wide application to monitor ungauged ephemeral channels in arid areas worldwide and provide insights about the dryland sedimentary system dynamics during extreme storm events.

How to cite: Cabré, A., Marc, O., Remy, D., and Carretier, S.: Integrating InSAR coherence and SAR amplitude to unravel the surface change processes operating during extreme rainstorm events in the Atacama Desert., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10362, https://doi.org/10.5194/egusphere-egu24-10362, 2024.

Extreme precipitation events drive landsliding in many regions across the globe and are an important part of the erosional cycle and related hazards. The intensity and frequency of extreme events are likely increasing due to rising global temperatures, causing greater future threat to society and an urgent need to quantify the relationships between surface process dynamics and extreme events. In steep mountain belts, orography also plays a role in focusing precipitation and intensifying erosion. Yet, the influence of orography on the intensity-duration characteristics of extreme precipitation remains a subject of debate because we lack spatially distributed and high time-resolution gauge datasets needed to resolve convective-scale, short-duration storm events and satellite-derived precipitation products struggle to accurately resolve precipitation gradients over areas of high relief and altitude. Annual periods of monsoon-related landsliding in the Himalaya offer a natural laboratory in which to explore relationships between extreme precipitation, orography and landsliding processes. Here we scale the NASA’s Global Precipitation Measurement (GPM) IMERG 30-minute, 0.1x0.1 degree product with local rain gauge data to produce high-temporal resolution records used to characterize extreme rainfall events (EREs) in central Nepal where hundreds of shallow landslides occur each summer. Individual storms from the time series are defined using the average inter-accumulation time as a measure for the minimum dry period between storms and extreme storms are extracted from the series using a 90^th percentile threshold for each gauge station. Variability in storm characteristics is defined using paired K-means agglomerative cluster and principal component analyses to evaluate spatial patterns in storm characteristics over a 10 year period compared to annual landslide inventories. Spatial patterns emerge that suggest orography increases the intensity and frequency of storms, which in turn focuses landsliding in specific, and potentially predictable, regions along the steep windward flank of the mountain belt.

How to cite: Clark, M., Plescher, R., Hille, M., Anderman, C., Chen, C.-M., Chamlagain, D., Zekkos, D., and West, A. J.: Quantifying surface process dynamics during extreme events from storm characteristics and landslide inventories, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18379, https://doi.org/10.5194/egusphere-egu24-18379, 2024.