Aug 2026· Discover Environment· Vol 4· 0 citations· 57 references
Abstract
Across the mountainous regions of the East African Rift, interactions between human activities and extreme rainfall events can intensify urban hydro-geomorphological hazards. Yet, observation remains challenging, as remote sensing in humid tropical terrains can be constrained by e.g., persistent cloud cover and dense canopy. This study focused on Uvira (Democratic Republic of the Congo), a city built on narrow alluvial fans along Lake Tanganyika’s northwestern shores, where recent rainfall events (2020-2021) culminated in severe floods. We examined the upstream-downstream sediment cascade to clarify the processes driving flood genesis. We applied an integrated approach combining extensive field observation campaigns, morpho-dimensional classification of 225 erosive events, Sentinel-2 imagery processed via Google Earth Engine, and statistical workflow. Results revealed a predominance of landslides (44.40%) and sheet erosion (38.20%), largely influenced by steep gradients between 900 and 1700 m. Statistical analysis (χ2 = 35.42; p > 0.05) showed no significant link between land-cover class and slope failures, suggesting that fragmented vegetation cover, likely linked to unplanned urbanization, may drive localized infiltration and slope instability. Hazards appeared controlled by dual rainfall regimes: seasonal accumulation (800-1000 mm) followed by short, intense pulses (e.g., 114 mm in 6 h). These conditions generated rapid hydro-sedimentary responses, with 3-4 m riverbed aggradation at the Kavimvira and Mulongwe River’s outlets, severely affecting downstream residential areas. Conversely, the Kalimabenge River carried a smaller sediment load, likely reflecting upstream reforestation. This work advances understanding of sediment connectivity and vegetation fragmentation in tropical rift environments. It highlights the need to move beyond curative dredging toward integrated watershed management, eco-protective measures, and participatory monitoring. Given the scarcity of hydrometeorological data in Uvira, these findings provide a baseline for land-use planning and risk reduction.
Landslide hazards along the Banihal–Ramban corridor of the Jammu–Srinagar National Highway (NH-44) represent a critical geoenvironmental challenge in Northwestern Himalaya, where active tectonics, fragile lithology, steep terrain, and increasing extreme precipitation interact with intensive infrastructure development. This technical note presents a focused analysis of flash floods and landslides of April 20, 2025, examining their triggering mechanisms, cascading geomorphic processes, and impacts on transportation infrastructure and settlements. Historical landslide records (1990–2025) and regional hydroclimatic observations are incorporated to contextualize the event within evolving patterns of hazard frequency and anthropogenic slope modification along the NH-44 corridor. The April 2025 disaster resulted from the localized high-intensity precipitation, which elevated pore-water pressures, reduced slope stability, and triggered multiple failures in structurally weakened rock formations. Results highlight a transition from isolated slope failures toward compound and cascading hazard scenarios involving flash floods, debris flows, and infrastructure disruption. The study underscores the increasing vulnerability of this strategic Himalayan lifeline. It emphasizes the need for geologically informed engineering design, improved drainage management, and integrated early warning strategies to enhance long-term resilience.
I. M. Bhat, Waseem Qader· Natural Hazards Review· 0 citations
Karst poljes are highly sensitive environments where natural hydro-meteorological extremes and human landscape alterations often collide. In February 2026, the Gembos, Eynif and Sobuca poljes in the Taurus Mountains experienced catastrophic flooding. To understand the driving mechanisms behind this disaster, we investigated the combined roles of extreme precipitation, sinkhole (ponor) blockage, and local engineering failures. By establishing a 10-year climatological baseline and utilizing multi-sensor satellite imagery (Sentinel-1 SAR and Sentinel-2 NDWI) within a GIS environment, we mapped the spatiotemporal evolution of the flood to isolate anthropogenic impacts. Our comparative multi-year analysis revealed that the basins successfully managed higher precipitation loads during the snow-dominated winter seasons of 2019 and 2022. However, in 2026, intense heavy rain created an abrupt volumetric shock. A targeted spatial bottleneck analysis demonstrated that the newly inaugurated D687 highway embankment effectively acted as a significant amplifying factor against this rapid runoff. This barrier severely disrupted the natural surface flow, trapped the floodwaters, and triggered a catastrophic tenfold expansion of the inundated area, ultimately causing the complete submersion of the highway itself. Furthermore, field observations confirmed that sediment and debris, exacerbated by upstream quarrying activities, physically clogged the ponors and crippled the karst system’s vertical drainage capacity. This cascading failure highlights a crucial lesson: treating active karst poljes as standard topographic basins during infrastructure planning inevitably leads to disaster. Our findings underscore the critical need for spatial planning that respects natural karst hydrodynamics, supported by continuous monitoring networks.
M. O. Baykara, Selahattin Akşit, Deniz Özgür· Carbonates and evaporites· 0 citations
Extreme precipitation events can cause long‐lasting changes to river systems, altering flood hazards beyond the initial disaster. We investigate how Typhoon Morakot (2009) impacted flood inundation patterns across four river catchments in southern Taiwan. Morakot triggered over 17,000 landslides, delivering large volumes of sediment to steep mountain rivers, reducing channel conveyance. Using aerial imagery and Structure from Motion photogrammetry, we constructed pre‐ and post‐event digital elevation models to quantify morphological changes. We simulated flood inundation using HEC‐RAS 2D across a range of discharges. Results show that sediment‐driven channel infilling increased inundation area by up to 44%. Areas with minimal sediment supply exhibited thalweg erosion, vegetation regrowth, and reduced inundation extent. These findings underscore the importance of including geomorphic change in flood hazard assessments, as landscape responses to extreme events can amplify, prolong, or reduce flooding hazards for years after the event.
B. Santos, B. Yanites, C. DeLisle et al.· Geophysical Research Letters· 0 citations
(English) Soil erosion in mountainous landscapes is strongly influenced by shallow landslides, particularly during extreme precipitation events. Despite their geomorphic significance, quantitative soil erosion studies often prioritize fine sediment dynamics and agricultural land-use calibrations, thereby underrepresenting the complexity of landslide processes driven by intrinsic slope parameters and external triggering forces.
This study examines sediment production and connectivity from shallow landslides under climate change and land-cover transitions. The primary objective aims to quantify sediment mobilization from slope instabilities to fluvial networks, focusing on the Saldes River Basin (102 km²) for model calibration and applying the results to the Upper Llobregat River Basin (504 km²).
The quantification approach used a distributed, event-based method with the FSLAM landslide stability model. Projected climate scenarios predict increased extreme precipitation events, resulting in heightened slope mass wasting. Future simulations indicate landslide mobilization rates increase by 10%, peaking at 16% during 20-year rainfall events. These findings underscore the significance of hillslope processes in sediment budget assessments and the role of extreme rainfall in sediment production.
To address sediment connectivity, this study introduces the Random Connect (RC) model. The model uses a random-walk framework and applies the Index of Connectivity (IC) to estimate sediment volume fluxes from source areas to channel networks. The input data includes a digital elevation model, IC maps, and sediment source maps derived from shallow landslides. The model outputs consist of raster maps that describe sediment flux. The receive maps show accumulated sediment volumes along transfer paths, and the release maps indicate the source cells contributing sediment to the target river.
The RC model application in the Saldes Basin highlighted how land cover affects sediment transport. Field surveys identified sediment hotspots and validated model outputs, incorporating forest cover as a factor in connectivity analyses. This enhanced IC methodology delineated transfer pathways, improving overland flow representation in RC simulations. Validation showed an average annual sediment budget of 1,545 t·km⁻²·year⁻¹, with the model estimating a sediment delivery ratio (SDR) of 0.34. Reservoir SDR values ranged from 0.12 to 0.24, illustrating the impact of connectivity thresholds on reservoir siltation.
A detailed LULC analysis in the ULRB shows that steep, sparsely vegetated areas have increased by 43%, leading to more bare soil and sediment sources. Conversely, forested slopes and vegetated areas act as buffers, reducing sediment delivery. However, climate projections suggest intensified rainfall and prolonged droughts may reduce vegetation resilience, reactivating sediment pathways. Results show that sediment production increases by up to 22% during extreme rainfall in future scenarios, while forest expansion can reduce sediment yield by up to 14%. Combined climate and land cover scenarios indicate non-linear responses, with far-future events generating up to 18% more sediment than baseline conditions.
The findings enhance understanding of sediment dynamics in reservoir-contributing basins, where traditional monitoring struggles to disentangle geomorphic processes. The study underscores the dual influence of forest recovery and extreme rainfall on sediment production and connectivity. The modelling framework provides a robust tool for sediment budget evaluation, aiding watershed management in erosion-prone mountainous areas.
(Català) L’erosió del sòl en paisatges muntanyosos està fortament condicionada pels despreniments superficials, especialment durant episodis de precipitació extrema. Tot i la seva rellevància geomorfològica, els estudis quantitatius sovint se centren en la dinàmica dels sediments fins i en calibracions vinculades a l’ús agrícola del sòl, subestimant la complexitat dels processos de despreniment, els quals depenen de paràmetres intrínsecs d’estabilitat i de forces externes desencadenants.
Aquest estudi analitza la producció i la conectivitat de sediments derivats de despreniments superficials sota escenaris de canvi climàtic i transicions en la cobertura del sòl. L’objectiu principal és quantificar la mobilització de sediments des d’inestabilitats de vessant cap a les xarxes fluvials, calibrant el model a la conca del riu Saldes (102 km²) i aplicant els resultats a la conca alta del riu Llobregat (504 km²).
La metodologia de quantificació va emprar un enfocament distribuït i basat en esdeveniments mitjançant el model d’estabilitat de vessants FSLAM. Els escenaris de canvi climàtic apunten a un augment d’episodis de precipitació extrema, on les simulacions indiquen increments en la mobilització de sediments d’aproximadament un 10%, amb pics del 16% en esdeveniments de període de retorn de 20 anys.
Per abordar la conectivitat de sediments, s’introdueix el model Random Connect (RC), que utilitza un càlcul de trajectòria aleatòria i aplica l’Índex de Conectivitat (IC) per estimar volums de fluxos de sediments des de les àrees font cap a les xarxes de drenatge. Les dades d’entrada inclouen models digitals d’elevació, mapes d’IC i mapes de fonts de sediments. Els resultats consisteixen en mapes de recepció que mostren volums acumulats al llarg de les trajectòries de transferència, mentre que els mapes de liberació indiquen les cel·les font que aporten sediments al riu objectiu.
L’estudi de conectivitat a la conca del Saldes va identificar punts crítics de sedimentació i va validar les zones de transferència, incorporant la cobertura forestal en la metodologia de l’IC. Això va permetre delimitar rutes de transferència, millorant la representació del flux superficial en les simulacions RC. La validació va mostrar un pressupost anual mitjà de sediments de 1545 t·km⁻²·any⁻¹, amb una relació d’aportació de sediments (SDR) estimada en 0,34. Els valors de SDR en la colmatació d’embassaments van oscil·lar entre 0,12 i 0,24, il·lustrant l’impacte dels llindars de conectivitat.
Un anàlisi de la cobertura vegetal a la conca alta del Llobregat mostra que les àrees escassament vegetades han augmentat un 43%, mentre que l’increment en zones boscoses actua com a amortidor, reduint l’aportació de sediments. Tanmateix, les projeccions climàtiques suggereixen que pluges intensificades i sequeres prolongades poden disminuir la resiliència de la vegetació, reactivant les rutes de sedimentació. Els resultats mostren que la producció de sediments augmenta fins a un 22% durant pluges extremes, mentre que l’expansió forestal redueix l’aportació en un 14%. Els escenaris combinats de clima i cobertura del sòl indiquen respostes no lineals, amb esdeveniments que generen fins a un 18% més de sediments que les condicions de referència.
Les troballes milloren la comprensió de la dinàmica de sediments en conques on el monitoratge tradicional té dificultats per separar processos geomorfològics. L’estudi destaca la doble influència de la recuperació forestal i de la pluja extrema en la producció i conectivitat de sediments. El marc de modelització ofereix una eina robusta per a l’avaluació de pressupostos de sediments, donant suport a la gestió de conques en àrees muntanyoses propenses a l’erosió.
(Español) La erosión del suelo en paisajes montañosos está fuertemente condicionada por deslizamientos superficiales, especialmente durante eventos de precipitación extrema. A pesar de su relevancia geomorfológica, los estudios cuantitativos suelen centrarse en la dinámica de sedimentos finos y en calibraciones vinculadas al uso agrícola del suelo, subestimando la complejidad de los procesos de deslizamiento, los cuales dependen de parámetros intrínsecos de estabilidad y de fuerzas desencadenantes externas.
Este estudio analiza la producción y conectividad de sedimentos derivados de deslizamientos superficiales bajo escenarios de cambio climático y transiciones en la cobertura del suelo. El objetivo principal es cuantificar la movilización de sedimentos desde inestabilidades de ladera hacia las redes fluviales, calibrando el modelo en la cuenca del río Saldes (102 km²) y aplicando los resultados a la cuenca alta del río Llobregat (504 km²). La metodología de cuantificación empleó un enfoque distribuido y basado en eventos mediante el modelo de estabilidad de laderas FSLAM. Los escenarios de cambio climático llevan a eventos de precipitación extrema donde las simulaciones indican incrementos en la movilización de sedimentos entre un 10%, con picos del 16% en eventos de retorno de 20 años.
Para abordar la conectividad de sedimentos, se introduce el modelo Random Connect (RC), el cual utiliza un cálculo de trayecto aleatorio y aplica el Índice de Conectividad (IC) para estimar volúmenes de flujos de sedimento desde áreas fuente hacia redes de drenaje. Los datos de entrada incluyen modelos digitales de elevación, mapas de IC y mapas de fuentes de sedimento. Los resultados consisten en los mapas de recepción que muestran volúmenes acumulados a lo largo de las trayectorias de transferencia, mientras que los de liberación indican las celdas fuente que aportan sedimentos al río objetivo.
El estudio de conectividad en la cuenca del Saldes identificó puntos críticos de sedimentación y validó las zonas de transferencia, incorporando la cobertura forestal en la metodología del IC y permitió delinear rutas de transferencia, mejorando la representación del flujo superficial en las simulaciones RC. La validación mostró un presupuesto anual promedio de sedimentos de 1545 t·km⁻²·año⁻¹, con una relación de aportación de sedimentos (SDR) estimada en 0,34. Los valores SDR en la colmatación de embalses oscilaron entre 0,12 y 0,24, ilustrando el impacto de los umbrales de conectividad.
Un análisis de la cobertura vegetal en la cuenca alta del Llobregat muestra que las ár
Extreme rainfall and flooding in May 2024 caused the most severe hydrological disaster ever recorded in Rio Grande do Sul, southern Brazil, exposing deep socio-environmental vulnerabilities. This study examines the spatial relationship between flood extent and changes in the structure and fragmentation of natural vegetation within the Guaíba Hydrographic Region, a multifunctional landscape integrating urban areas, agricultural systems, and sensitive ecosystems. We hypothesize that flooded areas exhibit higher levels of vegetation loss and fragmentation, whereas landscapes with greater pre-event continuity tend to experience lower relative loss. Using land use and land cover data for 2023 and 2024, combined with flood extent mapping and landscape metrics, we quantified post-event structural changes in vegetation. The multivariate structure of the landscape was synthesized using Principal Component Analysis, and spatial associations with flooding were assessed through local bivariate spatial autocorrelation. Results indicate a 25.2% reduction in natural vegetation cover, accompanied by an approximately 20% increase in the number of fragments and a loss of core-areas, indicating intensified fragmentation following the extreme event. The principal components captured three structural dimensions, size and morphospatial complexity, internal cohesion and connectivity, and spatial isolation, all of which declined between 2023 and 2024. Before the event, in 2023, the flooded areas were associated with larger and more cohesive fragments; after the event, these areas exhibited greater isolation and reduced connectivity. The findings partially support the hypothesis, indicating that fragmentation is not solely driven by flooding but emerges from the interaction between event intensity and pre-existing landscape fragility. The 2024 flood appears to have acted as a catalyst of pre-existing structural vulnerabilities, demonstrating that territorial resilience depends not only on vegetation extent but also on its spatial configuration and connectivity. These results highlight the need for planning strategies focused on ecological connectivity and watershed-scale management.
R. Weiss, Martiele Wilhelm, Ana Luisa Maffini et al.· Scientific Reports· 0 citations
Understanding the interplay between climate variability and human activities is essential for assessing long-term river flood hazards. Yet, the relative contributions of natural and anthropogenic drivers to flood magnitude remain poorly constrained due to limited multicentury records and insufficient integration of physical mechanisms with land-use histories. Here, we present the reconstruction of a 500-y history of Yangtze River flood variability using lake sediment archives, historical documents, and high-resolution climate reanalysis data. Our results reveal that flood frequency peaked during the Little Ice Age (~1500-1850 CE), driven by a weakened Western Pacific Subtropical High (WPSH), a southward-shifted Intertropical Convergence Zone (ITCZ), and enhanced southwesterly monsoonal moisture flux into the basin. These conditions were associated with El Niño-like tropical sea surface temperature (SST) anomalies and extratropical Rossby wave activity, highlighting the role of tropical-extratropical coupling in shaping flood-prone circulation regimes. Despite increased atmospheric temperature since 1850 CE, flood frequency declined, coinciding with a strengthened WPSH, a northward-shifted ITCZ, and the dominance of La Niña-like or neutral SST patterns. A nonstationary flood frequency model reveals that embankments and lake reclamation amplified the climate-driven 100-y flood magnitude by around 18% and 8%, respectively. These findings demonstrate that human interventions have intensified, rather than mitigated, the hydrological consequences of climatic forcing. Consistent with the recognition that flood risk is inherently nonstationary, our results provide empirical, multicentennial constraints on how atmospheric dynamics and landscape modification interact to shape flood hazards, highlighting the need for process-informed flood risk assessment in large river basins.
Shi‐Yong Yu, Zhixiong Shen, Jörg Franke et al.· Proceedings of the National...· 0 citations