Development of a data-driven model for spatial and temporal shallow landslide probability of occurrence at catchment scale

Open access funding provided by Universita degli Studi di Pavia within the CRUI-CARE Agreement. This work has been in the frame of the ANDROMEDA project, which has been supported by Fondazione Cariplo, grant no. 2017-0677.We thank the anonymous reviewers for their contributions in improving the paper. We thank Beatrice Corradini for the help in the collection of rainfall data and of shallow landslide events.A combined method was developed to forecast the spatial and the temporal probability of occurrence of rainfall-induced shallow landslides over large areas. The method also allowed to estimate the dynamic change of this probability during a rainfall event. The model, developed through a data-driven approach basing on Multivariate Adaptive Regression Splines technique, was based on a joint probability between the spatial probability of occurrence (susceptibility) and the temporal one. The former was estimated on the basis of geological, geomorphological, and hydrological predictors. The latter was assessed considering short-term cumulative rainfall, antecedent rainfall, soil hydrological conditions, expressed as soil saturation degree, and bedrock geology. The predictive capability of the methodology was tested for past triggering events of shallow landslides occurred in representative catchments of Oltrepò Pavese, in northern Italian Apennines. The method provided excellently to outstanding performance for both the really unstable hillslopes (area under ROC curve until 0.92, true positives until 98.8%, true negatives higher than 80%) and the identification of the triggering time (area under ROC curve of 0.98, true positives of 96.2%, true negatives of 94.6%). The developed methodology allowed us to obtain feasible results using satellite-based rainfall products and data acquired by field rain gauges. Advantages and weak points of the method, in comparison also with traditional approaches for the forecast of shallow landslides, were also provided.Universita degli Studi di Pavia within the CRUI-CARE AgreementFondazione Cariplo 2017-067

Identificazione preliminare delle aree idonee per i Sistemi di Drenaggio Sostenibile (SuDS) e le tecniche di Ricarica in condizioni controllate degli Acquiferi (MAR), per mitigare i fenomeni di allagamento dovuti a precipitazioni intense nella Città di Roma (Italia)

Questo articolo propone una metodologia di indagine preliminare e su larga scala per identificare le aree idonee ad approfondimenti di studio per l’applicazione di Sistemi di Drenaggio Sostenibile e le tecniche di Ricarica in Condizioni controllate degli acquiferi, che hanno lo scopo di incrementare la capacità naturale dell’acqua di infiltrarsi nel terreno, e il cui successo dipende fortemente dalle caratteristiche idrogeologiche e morfologiche di un’area. L’area di studio è la città di Roma dove l’obiettivo dell’applicazione di queste tecniche è quello di mitigare problematiche relative al surplus di acqua piovana che, in caso di eventi di precipitazione estremi, fatica ad infiltrarsi nel terreno, sovraccarica i sistemi di drenaggio, spesso sottodimensionati rispetto agli attuali regimi, e allaga lo spazio urbano. Il metodo proposto si avvale di analisi spaziali GIS dei dati di permeabilità delle litologie affioranti, del modello di elevazione del terreno e dei livelli piezometrici negli acquiferi. Per identificare le aree idonee, sono state individuate quelle aree caratterizzate da un’elevata permeabilità ed una soggiacenza della falda che conferisce all’acquifero una capacità volumetrica tale da essere potenzialmente in grado di immagazzinare maggiori quantità d’acqua, senza innescare problemi associati alla risalita della falda. I dati sono stati suddivisi in classi ed indicizzati per essere confrontati e combinati. In seguito, il risultato finale è stato confrontato con le segnalazioni di allagamenti urbani per comprendere dove la necessità di smaltire più acqua piovana corrisponda a zone potenzialmente favorevoli. I risultati dell’analisi effettuata mostrano che le condizioni favorevoli per applicare tali tecniche nella città di Roma siano abbastanza diffuse. L’ambiente geologico della città è caratterizzato da litologie permeabili con un effettivo potenziale di infiltrazione che permetterebbe all’acqua piovana di infiltrarsi nel sottosuolo e raggiungere la prima falda acquifera disponibile.This paper proposes a preliminary and large-scale survey methodology to identify areas suitable for indepth analysis for the application of Sustainable Drainage Systems and Managed Aquifer Recharge. These techniques are frequently applied to increase the natural infiltration capacity of water into the ground and their effectiveness depends on the local hydrogeological and morphological characteristics. The study area is the city of Rome where the aim is to mitigate the problems related to rainwater which, in case of extreme events, struggles to infiltrate into the ground, overloads the undersized drainage systems, and floods the urban space.The proposed method involves GIS geospatial analysis of the permeability of outcropping lithologies, the digital elevation model, and the piezometric levels of the aquifers. To identify the suitable zones, areas characterised by high permeability and a piezometric level that would confer a volumetric capacity to possibly store even large quantities of water, without triggering possible problems of water table rise, were identified. Data were divided into classes and indexed to compare and overlap them. Furthermore, the final result was compared with the urban flooding phenomena and the soil permeability map of Rome. The results of the performed analysis show that the preliminary suitable conditions to apply SuDS and MAR in Rome are widespread. The geological setting of the city is characterised by permeable lithologies in many places with an effective infiltration potential that would allow rainwater to infiltrate the subsoil and reach the first available aquifer.Ministry of Science and Innovation, Spain (MICINN) Spanish Government YC-2017-2333

Landslide displacement forecasting using deep learning and monitoring data across selected sites

Accurate early warning systems for landslides are a reliable risk-reduction strategy that may significantly reduce fatalities and economic losses. Several machine learning methods have been examined for this purpose, underlying deep learning (DL) models’ remarkable prediction capabilities. The long short-term memory (LSTM) and gated recurrent unit (GRU) algorithms are the sole DL model studied in the extant comparisons. However, several other DL algorithms are suitable for time series forecasting tasks. In this paper, we assess, compare, and describe seven DL methods for forecasting future landslide displacement: multi-layer perception (MLP), LSTM, GRU, 1D convolutional neural network (1D CNN), 2xLSTM, bidirectional LSTM (bi-LSTM), and an architecture composed of 1D CNN and LSTM (Conv-LSTM). The investigation focuses on four landslides with different geographic locations, geological settings, time step dimensions, and measurement instruments. Two landslides are located in an artificial reservoir context, while the displacement of the other two is influenced just by rainfall. The results reveal that the MLP, GRU, and LSTM models can make reliable predictions in all four scenarios, while the Conv- LSTM model outperforms the others in the Baishuihe landslide, where the landslide is highly seasonal. No evident performance differences were found for landslides inside artificial reservoirs rather than outside. Furthermore, the research shows that MLP is better adapted to forecast the highest displacement peaks, while LSTM and GRU are better suited to model lower displacement peaks. We believe the findings of this research will serve as a precious aid when implementing a DL-based landslide early warning system (LEWS).SUPPORTO SCIENTIFICO PER L’OTTIMIZZAZIONE, IMPLEMENTAZIONE E GESTIONE DEL SISTEMA DI MONITORAGGIO CON AGGIORNAMENTO DELLE SOGLIE DI ALLERTAMENTO DEL FENOMENO FRANOSO DI SANT’ANDREA – PERAROLO DI CADORE (BL)” and the Spanish Grant “SARAI, PID2020-116540RB-C21,MCIN/AEI/10.13039/501100011033” and “RISKCOASTInSAR displacement data of the El Arrecife landslideGeohazard Exploitation Platform (GEP) of the European Space AgencyNoR Projects Sponsorship (Project ID: 63737

Assessment of shallow landslide risk mitigation measures based on land use planning through probabilistic modelling

On October 25, 2011 an extreme rainfall event affected a wide area along the coasts of Cinque Terre (eastern Liguria, northern Italy). Particularly, in the Vernazza catchment, the event triggered hundreds of shallow landslides and a debris flood that caused three casualties. Investigation of slope stability after the event was carried out aiming at defining the most effective mitigation measures which may be adopted in future land use planning. To this objective a susceptibility model was produced and a series of scenarios were simulated using probabilistic methods. The susceptibility model has provided information about landslide conditioning factors on which to act for reducing landslide occurrence and therefore the associated risk. The simulations have taken into consideration the following alternative types of mitigation measures: (1) restoration of abandoned terraces, (2) reforestation of abandoned terraces, (3) use of local structural measures over stretches of potentially unstable hillsides and (4) avoidance of any intervention. The advantages and the disadvantages of proposed mitigation measures for shallow landslide risk are discussed considering the results of the simulations and taking into account their complex interaction with environmental, historical, cultural and socio-economic aspects. The results show that the most effective mitigation strategy for reducing landslide risk at short-term consists of applying structural measures over potentially unstable slopes. However a long-term program promoting the development of agricultural practices on terraced slopes is necessary. In fact, the simulations indicate if no measures are applied to avoid the degradation of the terraced areas, landslide areal frequency would inevitably increase

Potential and Limitations of Open Satellite Data for Flood Mapping

Satellite remote sensing is a powerful tool to map flooded areas. In recent years, the availability of free satellite data significantly increased in terms of type and frequency, allowing the production of flood maps at low cost around the world. In this work, we propose a semi-automatic method for flood mapping, based only on free satellite images and open-source software. The proposed methods are suitable to be applied by the community involved in flood hazard management, not necessarily experts in remote sensing processing. As case studies, we selected three flood events that recently occurred in Spain and Italy. Multispectral satellite data acquired by MODIS, Proba-V, Landsat, and Sentinel-2 and synthetic aperture radar (SAR) data collected by Sentinel-1 were used to detect flooded areas using different methodologies (e.g., Modified Normalized Difference Water Index, SAR backscattering variation, and supervised classification). Then, we improved and manually refined the automatic mapping using free ancillary data such as the digital elevation model-based water depth model and available ground truth data. We calculated flood detection performance (flood ratio) for the different datasets by comparing with flood maps made by official river authorities. The results show that it is necessary to consider different factors when selecting the best satellite data. Among these factors, the time of the satellite pass with respect to the flood peak is the most important. With co-flood multispectral images, more than 90% of the flooded area was detected in the 2015 Ebro flood (Spain) case study. With post-flood multispectral data, the flood ratio showed values under 50% a few weeks after the 2016 flood in Po and Tanaro plains (Italy), but it remained useful to map the inundated pattern. The SAR could detect flooding only at the co-flood stage, and the flood ratio showed values below 5% only a few days after the 2016 Po River inundation. Another result of the research was the creation of geomorphology-based inundation maps that matched up to 95% with official flood maps

Investigating gravitational grabens related to lateral spreading and evaporite dissolution subsidence by means of detailed mapping, trenching, and electrical resistivity tomography (Spanish Pyrenees)

The active lateral spread of the Peracalc Range (Spanish Pyrenees) has developed on a Cretaceous limestone sequence around 250 m thick, underlain by tectonically thickened (∼2.5 km) Triassic halite-bearing evaporites and clays. Outward expansion of the Triassic sequence by ductile deformation and probably halokinesis toward the debuttressed and unloaded front of the range has been accommodated in the overlying cap rock through the development of a striking horst and graben morphostructure. Fault scarps show anomalously high height to length ratios (aspect ratio; H max / L ) compared to the values reported for tectonic faults. This retrogressive gravitational deformation has aborted a paleodrainage, expressed as wind gaps, hanging valleys, and defeated streams. The significant vertical displacement component in this rock spread is attributed to subsidence caused by interstratal evaporite dissolution, as supported by the dissolution-induced collapse and graben structures mapped at the foot of the range. To our knowledge, the rock spread of Peracalc, covering around 4.5 km 2 and with a minimum volume of 0.9 km 3 , is the largest documented landslide of the Pyrenees. The excavation of trenches and the acquisition of electrical resistivity tomography profiles provided information on the thickness and subsurface structure of the graben fills, the age of the lateral spread (older than 45 ka), an unexpected episodic kinematic behavior of the gravitational faults, and the timing of deformation events, including slumping of lake deposits

Metamorphic Domes in Northern Tunisia: Exhuming the Roots of Nappe Belts by Widespread Post-Subduction Delamination in the Western Mediterranean

Cenozoic extension in the Western Mediterranean has been related to the dynamics of back-arc domains. Although, in most of its orogenic belts extension propagated into the fore-arc nappe domains. Here we revisit the structure, metamorphism and radiometric ages of the Tunisian Tell, where HP/LT rocks (350°C at 0.8 GPa), were exhumed by the sequential activity of extensional detachments after heating and decompression (410°C–440°C at 0.6–0.3 GPa) in a plate convergent setting. Normal faults thinning the Tunisian Tell detached at two different crustal levels. The shallower one cuts down into the Atlas Mesozoic sequence, involving Tellian Triassic evaporites in the hanging-wall forming halokinetic structures in the Mejerda basin late Miocene. The deeper-detachment bounds metamorphic domes formed by marbles and metapsammites from the Atlas domain. Illite crystallinity on Triassic rocks shows epizonal to anchizonal values, at deep and intermediate structural depths of the Tell-Atlas nappe belt, respectively. New U-Pb 49.78 ± 1.28 Ma rutile ages from Tellian metabasites, together with existing phlogopite 23–17 Ma K-Ar ages in Atlas marbles from the footwall of the deepest detachment, indicate a polymetamorphic evolution. The Tell rocks underthrusted the Kabylian flysch in the early Eocene. Further, early Miocene shortening thrusted the metabasites over lower-grade sediments, producing HP/LT metamorphism and ductile stretching at the base of the Atlas belt. The exhumation of midcrustal roots of Western Mediterranean nappe belts after tectonic shortening is a common feature related to tearing at the edges of the subduction systems and inboard delamination of their subcontinental lithospheric mantle.Ministerio de Ciencia e innovación PID2019- 107138RB-I00P18-RT-3632 of the Junta de Andalucia,Erasmus Mundus External Cooperation Window and by Scientific Cooperation Agreement 0534 between the Office National des Mines (ONM)The Tunis el Manar University and the Group for Relief and Active Processes Analysis (ARPA) from the University of GranadaTunisian Company of Petroleum Activities (ETAP)Universidad de Granada / CBU

Suitability of the SL index for the semi-automatic identification of mass movements affecting the drainage network

Los índices geomorfológicos, como el índice del gradiente del perfil longitudinal de los ríos (Stream Length- Gradient index, SL) han demostrado ser buenos identificadores de anomalías en los perfiles longitudinales de los ríos. Generalmente, los factores más comunes que producen estas anomalías (knickpoints) son principalmente cambios litológicos, estructuras tectónicas activas y grandes movimientos de ladera. Este estudio se propone detectar zonas de la red de drenaje afectadas por movimientos en masa utilizando el índice SL en las cuencas de La Vall d’Àssua, Romadriu y La Vall de Tor (Pirineos Centrales). La metodología utilizada consiste en calcular el índice SL utilizando la herramienta Chi-Map y, después, se han aplicado las herramientas Análisis de Puntos Calientes (Hotspot and Cluster Analysis, HCA) y Densidad de Kernel (Kernel Density, KD) de ArcGIS® para proporcionar una mejor visualización y localización de los valores anómalos del índice SL. Las anomalías de SL han sido comparadas con el inventario de inestabilidades de ladera existente en la cuenca de La Vall d’Àssua. Los resultados obtenidos de este análisis indican que hay una buena correlación entre anomalías de SL y los movimientos en masa. Además, este índice geomorfológico ha ayudado en la identificación de 13 nuevas inestabilidades de ladera en el conjunto de las tres cuencas analizadas. En conclusión, el estudio realizado ha permitido comprobar la utilidad del índice SL para detectar aquellos puntos de la red de drenaje que están afectados por movimientos en masa.Geomorphological indices, such as the Stream Length-Gradient (SL) index, have been demonstrated to be suitable for detecting anomalies in stream-profiles. These anomalies (knickpoints) are generally related to active tectonics, lithological changes and large mass movements. This study aims to detect drainage areas affected by mass movements using SL index in La Vall d’Àssua, Romadriu and La Vall de Tor basins (Central Pyrenees). The methodology used consists of computing the SL index using the Chi-Map script and then, applying two ArcGIS® tools, which are the Hotspot and Cluster Analysis (HCA) and Kernel Density (KD), to provide a better visualisation and location of the knickpoints. SL anomalies have been compared with the slope failure inventory of La Vall d’Àssua basin, indicating a good correlation between SL anomalies and slope failures. Additionally, this geomorphological index provided the identification of 13 mass movements which had not previously been described. To sum up, this geomorphological parameter is a useful tool for the identification of drainage network areas affected by mass movements.Este trabajo ha sido financiado por los Proyectos CHARMA (CGL2013-40828-R) y PROMONTEC (MINEICO- FEDER Ref.: CGL2017-84720-R)

Estimation of empirical rainfall thresholds for landslide triggering using partial duration series and their relation with climatic cycles. An application in southern Ecuador

Rainfall-induced landslides constitute a major cause of damage and fatalities throughout the intramontane basins of the Andes. The geological and climatic setting plays a key role in the generation of a high number of landslides in this area. For this reason, a greater understanding of the relationship between landslide frequency and climate conditions is necessary to mitigate human and economic losses.Accordingly, this paper presents an analysis of rainfall variables associatedwith a series of dated landslides (153 in total) in the southern Ecuador basin of Loja. This analysis was performed by applying an affordable empirical method that enables the calculation of critical rainfall threshold (CRT) curves. This calculation is based on an in-depth examination of rainfall parameters, such as cumulative precipitation and mean intensity, linked to a wide range of rainfall duration (from 1 to 90 days). The inspection of these parameters was addressed considering their frequency, which was calculated by using partial duration series (PDS), taking into account the entire rainfall record. This work has revealed that only 24% of landslides were triggered by rainfall conditions with maximum return periods greater than 1 year, whereas the rest did not exceed that return period. After finding the best correlation between the maximum return periods and the maximum mean intensity, a minimum power law function was adjusted to the CRTcurve that correlates duration and cumulative rainfall. The values for this CRT function resulted in 5.14 and 0.83 for its scaling constant (α) and shape parameter (β), respectively. In addition, a spectral analysis was conducted to detect climatic cycles on the entire rainfall record. In general, a clear correlation could not be established between climatic frequencies and significant rainfall events inducing landslides, although similarly return periods were found for a critical rainfall event of March 2015 (10.4 years) and the SUNSPOT cycles (10.5-12 years). The results derived from this research are significantly valuable for the prevention of future mass-movements, although additional data will be crucial to update and calibrate CRT curves to study the influence of climate on landslide event frequency and magnitude in Loja.Ministerio de Educación Superior, Ciencia, Tecnología e Innovación (SENESCYT)Instituto Nacional de Meteorología e Hidrología (INAMHI)Secretaría de Gestión de Riesgos (SNGR-Zona 7) del gobierno de EcuadorMinisterio de Economía y Competitividad de España a través del Programa "Juan de la Cierva

Coastal landslide reactivation caused by the urban development in the coastal fringe of Granada (Spain). DInSAR monitoring and damage inventory

The Marina del Este and Los Cármenes del Mar resorts, in the municipality of Almuñécar (Granada) were developed onto areas with large-dormant landslides, as they generally present a more gentle slope than adjacent stable zones. Consequently, landslides have been reactivated, as DInSAR results confirm. During the rainy winter 2009-2010, movements were accelerated. Severe damages in dwellings have been reported and some houses have been evacuated, causing a great social alarm. The present work shows the great requirement to take into account natural hazards in land-use planning and urban policy in hazardous areas in Spain, which is highly significant to protect the public from geological risksLas urbanizaciones de Marina del Este y Los Cármenes del Mar, en el municipio granadino de Almuñécar, se construyeron sobre antiguos deslizamientos costeros, aprovechando la topografía más suave que dejan las masas deslizadas. El urbanismo ha desencadenado la reactivación de los movimientos, cuyas tasas de velocidad han sido cuantificadas con técnicas DInSAR, registrando una importante aceleración durante el invierno lluvioso 2009-2010. Se han reconocido importantes daños en las viviendas, algunas de ellas ya desalojadas al presentar graves daños estructurales, lo que ha despertado una gran alarma social. El presente trabajo pone de manifiesto la imperiosa necesidad de incorporar los estudios de riesgos geológicos en la planificación urbanística y en la ordenación del territorio, asignatura pendiente de la legislación español