Marta González

Intense rainfall events often trigger landslides and torrential flows, which are not only hazardous processes on their own, but can also generate cascading hazards through sudden and massive sediment delivery to river networks. Slope processes are therefore key drivers of geomorphic change in mountainous catchments, enhancing hillslope-channel connectivity and promoting rapid channel reorganisation. In light of the above, it is essential to characterise structural and functional connectivity (Heckmann et al., 2018), as well as geomorphic organisation before and after intense precipitation events, to better evaluate flood hazards and associated risks. Against this background, the January 2020 Gloria storm affected the Tordera River basin (Catalonia, NE Spain), where more than 480 mm of rainfall was recorded over 96 hours, with 24-hour accumulation over 200 mm, causing widespread sediment mobilisation and channel changes, as well as significant damage due to flooding and landslides.In this study, we aim to evaluate: 1) how pre-event hillslope-channel connectivity influences the geomorphic response to extreme floods and the post-event geomorphic changes through an integrated analysis of the index of connectivity (IC); 2) the spatial distribution patterns of erosion and sedimentation through the geomorphic mapping of the active riverbed and sediment bars (both active and stable), before and after the Gloria storm, and the existing inventory of landslides caused by the event. High-resolution DTMs (Digital Terrain Models) were generated from airborne LiDAR surveys conducted in 2011, 2016, and 2023. The IC was derived from a pre-event DTM to characterise structural sediment connectivity following Cavalli et al. (2013), while erosion and sedimentation processes were quantified using the difference between DTMs (DTMs of Difference, DoDs) for pre-event (2016-2011) and post-event (2023-2016) periods. GIS-based geomorphic mapping of active channels and sediment bars before and after Gloria was used to assess event-scale channel reorganisation.Preliminary results indicate a clear spatial correspondence between pre-event connectivity patterns and the magnitude of the geomorphic change observed during that extreme flood. Areas characterised by high pre-event erosion rates, identified from 2016-2011 DoDs, largely coincide with sectors where numerous landslides were triggered during the Gloria storm. High connectivity values also correspond to areas dominated by erosion and deposition in the 2016-2011 DoDs, highlighting the role of pre-event structural connectivity in conditioning sediment transfer pathways. Furthermore, active bars mapped after the event predominantly overlap with areas affected by pre-event erosion, whereas bars that remained stable during the storm are mainly associated with zones characterised by pre-event deposition. The active channel also experienced noticeable widening during the event, while the majority of vegetated bars that were stable before Gloria remained stable throughout the storm, reinforcing the link between pre-event geomorphic organisation and flood response. These findings highlight the importance of pre-event structural connectivity in controlling geomorphic response during extreme rainfall events, providing valuable insight for hazard assessment and river management. Cavalli, M. et al. (2013). Geomorphometric assessment of spatial sediment connectivity in small Alpine catchments. Geomorphology, 188, 31-41.Heckmann, T. et al. (2018). Indices of sediment connectivity: opportunities, challenges and limitations. Earth-Science Reviews, 187, 77-108.

Coastal communities are increasingly vulnerable to storm impacts, highlighting the urgent need for predictive tools and enhanced preparedness. In this work, a comprehensive, high-resolution hydrodynamic operational service using the XBeach model is presented and tested for three urban beaches in Barcelona, NW Mediterranean Sea. The operational system is designed to provide early warnings of coastal flooding at a 3 d horizon. The operational architecture is based on Python scripts combined with task automation tools, ensuring a user-friendly system implemented on a standard desktop computer. Hydrodynamic validation of the model is carried out using data gathered during a field campaign in 2022, when a high-intensity storm occurred, resulting in a root mean square error of around 0.4 m and a skill score assessment index of 0.82. Flooding predictions were validated using videometry systems, yielding satisfactory Euclidean distances of less than 5 m for storms close to the topobathymetry collection. For storms occurring years earlier, the distances ranged between 7–15 m, underscoring the need for regular topobathymetry updates to maintain forecasting accuracy. The service provides a warning system with a specific categorisation of the event, enabling the end-users to prepare for a possible flooding. The strategy is currently running in operational mode, issuing alert warnings at the correct severity level. The outcome assists in decision-making relating to such events by utilising the operational system. The presented methodology is easily adaptable and replicable to meet user requirements or to be applied in other areas of interest.

A comprehensive, high-resolution hydrodynamic operational service using XBeach model is presented and tested for three urban beaches in Barcelona, NW Mediterranean Sea. The operational architecture is based on Python scripts combined with task automation tools, ensuring a user-friendly system implemented on a standard desktop computer. Hydrodynamic validation of the model is carried out using data gathered during a field campaign in 2022, when a high-intensity storm occurred, resulting in a root mean square error of around 0.4 m and a skill score assessment index of 0.82. Flooding predictions were validated using videometry systems, yielding satisfactory Euclidean distances less than 5 m for storms close to the topobathymetry collection. For storms occurring years earlier, the distances ranged between 7–15 m, underscoring the need for regular topobathymetry updates to maintain forecasting accuracy. The operational system is designed to provide early-warning coastal flooding at three-days horizon. The service provides a warning system with a specific categorisation of the event, enabling the end-users to prepare for a possible flooding. The outcome assists in decision-making of such events by utilizing the operational system. The presented methodology is easily adaptable and replicable to meet user requirements or to be applied in other areas of interest.

A comprehensive, high-resolution hydrodynamic operational service using XBeach model is presented and tested for three urban beaches in Barcelona, NW Mediterranean Sea. The operational architecture is based on Python scripts combined with task automation tools, ensuring a user-friendly system implemented on a standard desktop computer. Hydrodynamic validation of the model is carried out using data gathered during a field campaign in 2022, when a high-intensity storm occurred, resulting in a root mean square error of around 0.4 m and a skill score assessment index of 0.82. Flooding predictions were validated using videometry systems, yielding satisfactory Euclidean distances less than 5 m for storms close to the topobathymetry collection. For storms occurring years earlier, the distances ranged between 7–15 m, underscoring the need for regular topobathymetry updates to maintain forecasting accuracy. The operational system is designed to provide early-warning coastal flooding at three-days horizon. The service provides a warning system with a specific categorisation of the event, enabling the end-users to prepare for a possible flooding. The outcome assists in decision-making of such events by utilizing the operational system. The presented methodology is easily adaptable and replicable to meet user requirements or to be applied in other areas of interest.

A comprehensive, high-resolution hydrodynamic operational service using XBeach model is presented and tested for three urban beaches in Barcelona, NW Mediterranean Sea. The operational architecture is based on Python scripts combined with task automation tools, ensuring a user-friendly system implemented on a standard desktop computer. Hydrodynamic validation of the model is carried out using data gathered during a field campaign in 2022, when a high-intensity storm occurred, resulting in a root mean square error of around 0.4 m and a skill score assessment index of 0.82. Flooding predictions were validated using videometry systems, yielding satisfactory Euclidean distances less than 5 m for storms close to the topobathymetry collection. For storms occurring years earlier, the distances ranged between 7–15 m, underscoring the need for regular topobathymetry updates to maintain forecasting accuracy. The operational system is designed to provide early-warning coastal flooding at three-days horizon. The service provides a warning system with a specific categorisation of the event, enabling the end-users to prepare for a possible flooding. The outcome assists in decision-making of such events by utilizing the operational system. The presented methodology is easily adaptable and replicable to meet user requirements or to be applied in other areas of interest.

The interaction between slope instability processes and river dynamics often triggers a cascade effect. Sediment influx from slopes can obstruct rivers, leading to upstream flooding and potential catastrophic flash floods downstream upon dam breakage. In addition, the incision of the drainage network steepens the valley hillslopes, further exacerbating slope instability processes, modifying the geomorphology and the sedimentary fluxes and increasing the occurrence of landslide-derived hazards.In this regard, a comprehensive and updated landslide inventory, especially focusing on the interconnection between landslides and drainage networks, is crucial for effective hazard assessment considering these cascading effects induced by slope and fluvial processes.This study presents advancements in landslide mapping by integrating data from Multi-Temporal Synthetic Aperture Radar (MT-InSAR) and landscape evolution analysis through geomorphological indices such as Chi, Normalized Channel Steepness Index (Ksn) and Stream Length-Gradient Index (SL). Identification of anomalies along rivers using Ksn and SL (knickpoints or knickzones) aided in pinpointing abnormal slopes due to sediment influx from landslides. Additionally, active areas were delineated using the ADAfinder tool, extracting data from MT-InSAR provided by the European Ground Motion Service (EGMS). This multi-technique analysis highlighted the slopes of interest. Landslides identified with these techniques were delimited and characterized in terms of type assignment, using 2x2 m DTM hillshades derived from airborne LiDAR data and field observations.The upper catchments of the Garona and Noguera Pallaresa rivers (central Pyrenees-NE Spain) were selected as study cases. The study highlights the disequilibrium in the watershed divide between Noguera Pallaresa and Garona basins, suggesting a transition toward equilibrium favouring a main divide migration towards the Noguera Pallaresa due to hillslope processes. The assessment of the equilibrium profile geometry of the Noguera Pallaresa river at a regional scale suggests at least two main knickpoints. The river sections downstream of the knickpoints are associated with landslides triggered by post-glacial dynamics and incision wave effects. Combining SL and Ksn curves with Active Deformation Areas (ADA) underscores areas with potentially reactivating deep-seated landslides, signifying potential high damages in case of low-probability but catastrophic reactivations.In conclusion, the integration of diverse methodologies shed light on the spatial relationship between transient features in the landscape (knickpoints) and landslide occurrence, emphasizing the need for a comprehensive approach to mitigate landslide and fluvial risks in the Noguera Pallaresa and Garona river basins.

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.

A comprehensive, high-resolution hydrodynamic operational service using XBeach model is presented and tested for three urban beaches in Barcelona, NW Mediterranean Sea. The operational architecture is based on Python scripts combined with task automation tools, ensuring a user-friendly system implemented on a standard desktop computer. Hydrodynamic validation of the model is carried out using data gathered during a field campaign in 2022, when a high-intensity storm occurred, resulting in a root mean square error of around 0.4 m and a skill score assessment index of 0.82. Flooding predictions were validated using videometry systems, yielding satisfactory Euclidean distances less than 5 m for storms close to the topobathymetry collection. For storms occurring years earlier, the distances ranged between 7–15 m, underscoring the need for regular topobathymetry updates to maintain forecasting accuracy. The operational system is designed to provide early-warning coastal flooding at three-days horizon. The service provides a warning system with a specific categorisation of the event, enabling the end-users to prepare for a possible flooding. The outcome assists in decision-making of such events by utilizing the operational system. The presented methodology is easily adaptable and replicable to meet user requirements or to be applied in other areas of interest.

A comprehensive, high-resolution hydrodynamic operational service using XBeach model is presented and tested for three urban beaches in Barcelona, NW Mediterranean Sea. The operational architecture is based on Python scripts combined with task automation tools, ensuring a user-friendly system implemented on a standard desktop computer. Hydrodynamic validation of the model is carried out using data gathered during a field campaign in 2022, when a high-intensity storm occurred, resulting in a root mean square error of around 0.4 m and a skill score assessment index of 0.82. Flooding predictions were validated using videometry systems, yielding satisfactory Euclidean distances less than 5 m for storms close to the topobathymetry collection. For storms occurring years earlier, the distances ranged between 7–15 m, underscoring the need for regular topobathymetry updates to maintain forecasting accuracy. The operational system is designed to provide early-warning coastal flooding at three-days horizon. The service provides a warning system with a specific categorisation of the event, enabling the end-users to prepare for a possible flooding. The outcome assists in decision-making of such events by utilizing the operational system. The presented methodology is easily adaptable and replicable to meet user requirements or to be applied in other areas of interest.

A comprehensive, high-resolution hydrodynamic operational service using XBeach model is presented and tested for three urban beaches in Barcelona, NW Mediterranean Sea. The operational architecture is based on Python scripts combined with task automation tools, ensuring a user-friendly system implemented on a standard desktop computer. Hydrodynamic validation of the model is carried out using data gathered during a field campaign in 2022, when a high-intensity storm occurred, resulting in a root mean square error of around 0.4 m and a skill score assessment index of 0.82. Flooding predictions were validated using videometry systems, yielding satisfactory Euclidean distances less than 5 m for storms close to the topobathymetry collection. For storms occurring years earlier, the distances ranged between 7–15 m, underscoring the need for regular topobathymetry updates to maintain forecasting accuracy. The operational system is designed to provide early-warning coastal flooding at three-days horizon. The service provides a warning system with a specific categorisation of the event, enabling the end-users to prepare for a possible flooding. The outcome assists in decision-making of such events by utilizing the operational system. The presented methodology is easily adaptable and replicable to meet user requirements or to be applied in other areas of interest.