Exceptional Rainfall Events Research Articles

October 2023. A mild but very changeable month exceptional rainfall events in Scotland

October 2023. A mild but very changeable month exceptional rainfall events in Scotland

Was the extreme rainfall that caused the August 2022 flood in Pakistan predictable?

Pakistan suffered from severe floods in the past, but in August 2022, the country experienced exceptional extreme rainfall events that caused widespread and catastrophic flooding. The 2022 flood affected all aspects of socio-economic lives including agriculture, infrastructure, and mortality of humans and livestock. The two-day accumulated extreme rainfall on 17–18 August was anomalous and contributed the most to the flood in the southern provinces of Pakistan. The damage caused by extreme rainfall and the subsequent flooding has raised questions regarding the predictability of extreme rainfall by the existing weather forecasting models. Here, we use ensemble forecasts from four numerical weather prediction models under THORPEX Interactive Grand Global Ensemble datasets to examine the predictability of extreme rainfall at a six-day lead. The extreme precipitation during 17–18 August 2022 was predictable a week before the event that contributed the most to the flooding. All the forecast models provided an early warning at a six-day lead time. UK Meteorological Office and European Centre for Medium-Range Weather Forecasts models produced comparable results to observations at all the lead times. Our findings highlight that an integrated framework of extended quantitative precipitation forecasts and hydrological modeling can help reduce the country’s flood vulnerability and risk associated with it.

Failure Mechanism of a Rainfall-Triggered Landslide in Clay Slopes

In December 2013, a portion of a large and deep ancient landslide on the southern slope of the Montescaglioso town (Basilicata, Southern Italy) was abruptly reactivated, as a consequence of exceptional rainfall events, causing relevant damages to structures and infrastructures. The sliding surface is supposed to be located within a thick deposit of Pleistocene stiff clays overlain by dislocated blocks of calcarenites and cemented conglomerates. This paper discusses the research carried out to investigate the failure mechanism that occurred during the landslide event and the factors that controlled the reactivation. To this purpose, geological and geomorphological analyses were first proposed, followed by a back-analysis of the landslide process, performed via limit equilibrium calculations implementing time-dependent pore water pressure distributions derived from transient seepage finite element analyses. Furthermore, the overall landslide mechanism was investigated through a three-dimensional finite element analysis, built using the monitoring campaign carried out in the post-failure stage and calibrated according to the in situ failure mechanism evidence. Both the limit equilibrium and finite element analyses provide results in good agreement with the geomorphological evidence, further allowing us to recognize the effects of rainfall infiltration in the increase of pore water pressure along the sliding surface and the variation of the stress–strain state leading to failure occurrence.

Learning ensembles of deep neural networks for extreme rainfall event detection

Accurate rainfall estimation is crucial to adequately assess the risk associated with extreme events capable of triggering floods and landslides. Data gathered from Rain Gauges (RGs), sensors devoted to measuring the intensity of the rain at individual points, are commonly used to feed interpolation methods (e.g., the Kriging geostatistical approach) and estimate the precipitation field over an area of interest. However, the information provided by RGs could be insufficient to model complex phenomena, and computationally expensive interpolation methods could not be used in real-time environments. Integrating additional data sources (e.g., radar and geostationary satellites) is an effective solution for improving the quality of the estimate, but it needs to cope with Big Data issues. To overcome all these issues, we propose a Rainfall Estimation Model (REM) based on an Ensemble of Deep Neural Networks (DeepEns-REM) that can automatically fuse heterogeneous data sources. The usage of Residual Blocks in the base models and the adoption of a Snapshot procedure to build the ensemble guarantees a fast convergence and scalability. Experimental results, conducted on a real dataset concerning a southern region in Italy, demonstrate the quality of the proposal in comparison with the Kriging interpolation technique and other machine learning techniques, especially in the case of exceptional rainfall events.

Assessing the 2022 Flood Impacts in Queensland Combining Daytime and Nighttime Optical and Imaging Radar Data

In the Australian summer season of 2022, exceptional rainfall events occurred in Southeast Queensland and parts of New South Wales, leading to extensive flooding of rural and urban areas. Here, we map the extent of flooding in the city of Brisbane and evaluate the change in electricity usage as a proxy for flood impact using VIIRS nighttime brightness imagery. Scanning a wide range of possible sensors, we used pre-flood and peak-flood PlanetScope imagery to map the inundated areas, using a new spectral index we developed, the Normalized Difference Inundation Index (NDII), which is based on changes in the NIR reflectance due to sediment-laden flood waters. We compared the Capella-Space X-band/HH imaging radar data captured at peak-flood date to the PlanetScope-derived mapping of the inundated areas. We found that in the Capella-Space image, significant flooded areas identified in PlanetScope imagery were omitted. These omission errors may be partly explained by the use of a single-date radar image, by the X-band, which is partly scattered by tree canopy, and by the SAR look angle under which flooded streets may be blocked from the view of the satellite. Using VIIRS nightly imagery, we were able to identify grid cells where electricity usage was impacted due to the floods. These changes in nighttime brightness matched both the inundated areas mapped via PlanetScope data as well as areas corresponding with decreased electricity loads reported by the regional electricity supplier. Altogether we demonstrate that using a variety of optical and radar sensors, as well as nighttime and daytime sensors, enable us to overcome data gaps and better understand the impact of flood events. We also emphasize the importance of high temporal revisit times (at least twice daily) to more accurately monitor flood events.

The impacts of exceptional rainfall on phosphorus mobilisation in a mountain agroforestry catchment (NE, Spain)

Erosion causes significant soil and nutrient losses that can reach streams and degrade habitats. Phosphorus (P) is among the nutrients of greatest concern for water pollution. Due to the increase in the number of storm events over the last decade, which could rise further under climate change scenarios, a more in-depth analysis of the effect of rainfall on the behaviour of P in fragile environments is needed. Little is known about the mobilisation and export of P in mountainous Mediterranean agroecosystems. To contribute to this knowledge, this research analysed the variability of P in the sediments of streambeds of different orders in an agroforestry area of the Northern Ebro Basin (Aragón, Spain) following an exceptional rainfall event; the implications of different land uses were also explored. Sediment composition was assessed before and after the rainfall event in three nested subcatchments and then related to soil properties. Phosphorus was mostly linked to the mineral fraction (mainly to silicates), while the links between P with clay and organic matter (P-clay, P-OM) were very weak. The P-OM links occurred only in the soils of forested areas. Agricultural lands, which are prone to erosion and had the highest P concentrations, contribute to P release. However, the streambeds and the lateral erosion of channel banks by floods triggered by the rainfall event should be considered as the main contributors to the export of P. The high intensity rainfall event led to 35% and 60% reductions in clay and OM, respectively, and to an enrichment of P in the sediments, the concentrations of which were lower in the headwaters than downstream. This means that the P in streambeds remains exposed in relatively high concentrations following extreme rainfall events with implications for the P cycle and water pollution.

Analysis of water and soil conservation techniques at the Ain Sefra arid watershed (Ksour Mountains, southwest Algeria).

In Algeria, the arid steppe watershed currently suffers from serious environmental problems, including land degradation, poor water resource management, soil conservation, and land cover management. This situation is manifested by several events such as soil erosion, depletion of water resources, and loss of biodiversity, which are partly related to the acceleration of the soil degradation process. In order to improve the functioning of ecosystems in these watersheds, public authorities and farmers have undertaken restoration and protection efforts through land-use planning programs. The objective of this study is to test the stability, reliability, and anti-erosion effectiveness of these anti-erosion developments that currently exist on three sites, Sfissifa, Belguered, and Ain Sefra, in the face of the exceptional extreme rainfall events recorded especially in 2007-2008 (250mm), both on cultivated land and in pasture and forest areas. We found that the traditional techniques generally used by farmers (terraces, stone cordons, toub walls, use of manure, cultivation in tanks and on ridges) have a great positive impact on water and soil conservation at the level of the cultivated plots. In addition, the modern techniques developed by the State (torrential correction, hill retention, reforestation) have proved to be very useful for water and soil conservation on a large scale, i.e., at the level of watersheds. This combination of these two types of development is almost indispensable to ensure a very positive impact on land productivity and the reduction of the risk of degradation.

Earthquakes and extreme rainfall induce long term permeability enhancement of volcanic island hydrogeological systems

Earthquakes affect near-surface permeability, however temporal permeability evolution quantification is challenging due to the scarcity of observations data. Using thirteen years of groundwater level observations, we highlight clear permeability variations induced by earthquakes in an aquifer and overlaying aquitard. Dynamic stresses, above a threshold value PGV > 0.5 cm s−1, were mostly responsible for these variations. We develop a new model using earth tides responses of water levels between earthquakes. We demonstrate a clear permeability increase of the hydrogeological system, with the permeability of the aquifer increasing 20-fold and that of the aquitard 300-fold over 12 years, induced by fracture creation or fracture unclogging. In addition, we demonstrate unprecedented observations of increase in permeability due to the effect of extreme tropical deluges of rainfall and hurricanes. The water pressure increase induced by the exceptional rainfall events thus act as piston strokes strong enough to unclog congested fractures by colloids, particles or precipitates. Lastly, an analysis of regional permeabilities also highlights a permeability increase over geological timeframes (× 40 per million years), corroborating the trend observed over the last decade. This demonstrates that permeability of aquifers of andesitic volcanic islands, such as the Lesser Antilles, significantly evolve with time due to seismic activity and extreme rainfall.

Riesgos de Erosión e Inundaciones en las Cuencas Margosas de las Montañas Prerif Orientales (Marruecos): Una Respuesta a Eventos Climáticos Excepcionales o/a la Presión Antropogénica.

The Eastern Rif Mountains are frequently subject to exceptional rainfall events, whose consequences are sometimes disastrous. The impact of these phenomena on environments is more important as the majorities of slopes are bare and subject to strong human influence. The protective natural forests of the slopes are almost destroyed; they currently cover only a few peaks of mountains in the region. They represent 1.84% of the total area of wadi Tleta sub-basin and only 1.32% of the Tarmast wadi sub-basin. However, croplands, occupying respectively 60% and 34% in the two sub-basins, extend even on the steepest slopes. Similarly, the accelerated and uncontrolled human occupation of the urban peripheries, located downstream of the basins, amplifies the vulnerability of these environments to the hydrological hazards, that threaten several sites surrounding the agglomeration of Taza. Thus, the whole region is subject to different degradation processes. Hydric erosion affects the majority of the slopes; it causes excessive sediment production that may exceed 60 t ha -1 year -1 in some sub-basins. Similarly, flood disasters are quite common in the region. The flood of 20/9/2000 is a reference, with a volume estimated at 4 million m 3 (DRH-Sebou 2000). Human and material damage was enormous in the rural centers and in the northern outlying districts of Taza. This contribution aims to present and analyze the combined impacts of the extreme rains and the actions of the human societies on the dynamics of the prerifain environment and its adjoining spaces.

Assessment of an Extreme Rainfall Detection System for Flood Prediction over Queensland (Australia)

Flood events represent some of the most catastrophic natural disasters, especially in localities where appropriate measurement instruments and early warning systems are not available. Remotely sensed data can often help to obtain near real-time rainfall information with a global spatial coverage without the limitations that characterize other instruments. In order to achieve this goal, a freely accessible Extreme Rainfall Detection System (ERDS—erds.ithacaweb.org) was developed and implemented by ITHACA with the aim of monitoring and forecasting exceptional rainfall events and providing information in an understandable way for researchers as well as non-specialized users. The near real-time rainfall monitoring is performed by taking advantage of NASA GPM (Global Precipitation Measurement) IMERG (Integrated Multi-satellite Retrievals for GPM) half-hourly data (one of the most advanced rainfall measurements provided by satellite). This study aims to evaluate ERDS performance in the detection of the extreme rainfall that led to a massive flood event in Queensland (Australia) between January and February 2019. Due to the impressive amount of rainfall that affected the area, Flinders River (one of the longest Australian rivers) overflowed, expanding to a width of tens of kilometers. Several cities were also partially affected and Copernicus Emergency Management Service was activated with the aim of providing an assessment of the impact of the event. In this research, ERDS outputs were validated using both in situ and open source remotely sensed data. Specifically, taking advantage of both NASA MODIS (Moderate-resolution Imaging Spectroradiometer) and Copernicus Sentinel datasets, it was possible to gain a clear look at the full extent of the flood event. GPM data proved to be a reliable source of rainfall information for the evaluation of areas affected by heavy rainfall. By merging these data, it was possible to recreate the dynamics of the event.

Fingerprinting changes in source contribution for evaluating soil response during an exceptional rainfall in Spanish pre-pyrenees

In the Mediterranean region, floods are expected to increase as a result of climate change and knowledge of soil erosion hot spots during exceptional rainfalls is required to support mitigation measures. This study quantifies the main sediment sources during an exceptional rainfall event in 2012 (235 mm) at the outlet of two catchments located in NE Spain. To this purpose, suspended sediments were collected during the flood event, complemented with entrapped sediments in mat taken one year after the event. We used fingerprinting methodology and applied the FingerPro unmixing model to estimate the contribution from main sources. The selected tracers clearly distinguished agricultural, rangeland, subsoil and channel banks as the four potential sources in both catchments. In the Vandunchil catchment, the 8 time-integrated suspended sediment samples revealed changes in source contribution during the 2-h sampling sequence. There were relatively high contributions from rangeland, agriculture and subsoil at the beginning of the sampling, representing 30, 40 and 35% of the total source contributions, respectively. Our records captured the delivery of pulses of eroded surface soil transported by runoff with direct connectivity to the stream. The sequence was followed by a sharp increase in channel bank contribution (up to 90%) in comparison to the other sources, reflecting streambank erosion and landslide occurrence, which manifested during the flood. In contrast, in the La Reina catchment, agricultural soils contributed the most (65%) and, together with subsoils (32%), were the main sources. These results reflect the effect of the higher connectivity and slope gradient of these cultivated fields of the La Reina catchment in comparison with those of the Vandunchil catchment.We discuss the possibility of using different properties, such as radionuclides, geochemistry and magnetic measurements, as tracers to distinguish between potential sources during an exceptional event in upland Mediterranean catchments. Our results support the use of fingerprinting techniques to determine variations in source contribution and sediment provenance during flood events, as extreme rainfalls are main drivers of sediment mobilization and key factors in changing landscapes. This is essential in identifying vulnerable hot spots, in which early-stage interventions are needed, and for helping policy makers with management of soil and water resources.

MOBILIZACE CHEMICKÝCH SLOŽEK STRUSKOVÉ DEPONIE V NÁRODNÍ PŘÍRODNÍ REZERVACI RUDICKÉ PROPADÁNÍ

The Rudice swallow hole (Rudické propadání) National Nature Monument is a locality affected by occasional mass movements and landslides. During exceptional rainfall events, the slag material from the slopes of a small valley called “Ve struskách” (“In the Slags”) slides into an episodic stream, which enters the local karst system near the swallow hole of the Jedovnice Creek (Jedovnický potok).The slag was dumped in the locality in consequence of the past processing of iron ore in blast furnaces, which had been built near Jedovnice by the princely Salm family in the 19th century. Even though the blast furnaces were closed down a hundred years ago, the slag components leaking into the Rudice stream sink cave system still demonstrably damage the speleothems. This was the majorimpulse for us to have a closer look at the geochemical properties of the slag.The chemical composition was determined by silicate analyses carried out in the Institute of Geological Sciences at the Faculty of Sciences of the Masaryk University in Brno and in the ACME laboratories in Canada. The ACME laboratories determined heavy metal contents by atomic absorption spectroscopy (AAS) and by inductively coupled plasma mass spectrometry (ICP-MS). The petrographic characterization of the slag and its enclosures was conducted based on point analyses by a wavelength dispersive X ray (WDX) electron microprobe. Predictions regarding the geochemical behavior of the slag components in an aqueous environment were made using the sequential extraction analysis (SEA) according to Tessier (1979).We have found the expected spatial variability of the basic chemical composition of the slag dumps, as well as the presence of heavy metals (cadmium and especially zinc are present at high concentrations).The slag material exhibits a glassy amorphous structure containing occasional mineral crystals, droplets of pure or oxidized iron and fragments of other materials (such as charcoal or blast furnace bricks). The ongoing weathering of the slag is accompanied by oxidation of crude iron and formation of limonite. Apart from that, the material is not subject to signifi cant secondary transformations. The results of the sequential extraction analyses of slag and soil samples suggest that Cd and Zn are chemically bound to the “carbonate fraction”, which, in general, tends to dissolve under acidic conditions. Even though the environment of the carbonate rock cave systems is typically alkaline, there is a persisting risk of mobilization of heavy metals by acid soil solutions. From the environmental point of view, the slag deposition primarily represents a source of clastic material, which contaminates the cave system and damages speleothems by mechanical abrasion.

Geomechanical response of an abandoned chalk mine to multi-annual water table fluctuations

The Paris basin contains 35,000–40,000 mines, most of which are abandoned, having mined chalk, a rock very sensitive to water. Although they have been excavated above the groundwater level, some of the mines can be temporarily or permanently flooded, due to (some) exceptional rainfall events. We have thus instrumented the chalk mine of Estreux (Nord department) to measure the impact of the oscillations of the water table on the stability of one of its pillars. It is a mine dug around 20 m deep by the chambers and pillars method. Now abandoned, it is temporarily flooded when the water table, located a few meters below the mine floor, rises due to heavy precipitation, which occurs on average every 8 years. From 2004 to 2012, a pillar was equipped with a convergence rod and two extensometers. There is a correlation between the vertical and horizontal deformation rates of the pillar and the periodic rise in the water table. Chalk samples were also taken in situ and their geomechanical properties characterized in the laboratory. On this basis, a first 3D mechanical simulation of the behavior of this pillar has been carried out taking into account elasticity, plasticity and creep. The calculated mean values of deformation generally match the measurements, and the model succeeds in reproducing the annual fluctuations of these parameters in relation to those of the level of the water table. However, compared to the measurements carried out in situ, the current model exaggerates the vertical deformations compared to the horizontal deformations. However, with this first model, we can observe that the variations in the water table induce elastic and reversible deformations of the pillar, given the absence of plastification of the chalk. These deformations are complementary to those due to the creep induced by the weight of the overlying grounds. If we want to model the long-term behavior of the pillar, particularly under the effect of the fluctuations of the water table induced by the climate change in progress, it is necessary to improve this model, taking into account the hydromechanical couplings and the flows in unsaturated condition. In conclusion, it is proposed to use these data later in a complete mechanical model, still under development at INERIS.

Evaluating the 4th November 2015 Flash Flood Disaster : A Case Study in Wadi An-Natrun and Wadi Al-Farigh Depressions, The Western Desert, Egypt

Flash floods are among natural hazards frequently recorded in Egyptian deserts. By the November 4, 2015 a sever flash flood hit the northwestern part of the Nile Delta and the surrounding desert margin in Wadi An-Natrun and Wadi Al-Farigh Depressions. This event left large economic damage and fatalities. In the current study, field work has been carried out in disaster sites, namely in Wadi An-Natrun and Wadi Al-Farigh. This allows a detailed observation of flood impacts. Also Landsat-based spectral indices and GIS change detection operations are utilized in quantifying damage. It is found that physical factors such as exceptional rainfall event and topography control flood runoff and inundation. Moreover, miss-land use in the study area yields a disastrous flash flood.

Evolution Des Indices Pluviométriques Extrêmes Par L'analyse De Modèles Climatiques Régionaux Du Programme CORDEX: Les Projections Climatiques Sur Le Sénégal

This study aims at characterizing the extreme rainfall events over West Africa particularly in the Sahel region and Senegal by 2100 (far future) under the greenhouse gas emission scenario RCP8.5 by analyzing the simulations of four (4) regional climate models (RCMs) of CORDEX (Regional COordinated climate Downscaling Experiment) program. The study of these extreme climate indices is crucial for the understanding of the impacts of climate change on some vital socio-economic sectors such as the agriculture in Sahel and Senegal. The results show that almost all the RCMs predict a decrease of the rainfall over most parts of the Sahel region particularly over the Western Sahel. The analysis of the climate indices such as the highest one day precipitation amount, the 99th percentile and the maximum dry spell length (CDD) shows that the RCMs (except CanRCM4) project an increase of these exceptional rainfall events over the Sahel (especially over the Western Sahel) by 2100. In Senegal, the RCMs (except RCA4) agree on a decrease of the precipitation and the number of wet days by 2100. When considering the evolution of rainfall events intensity, the highest one day precipitation amount and the 99th percentile, the RCMs (except CanRCM4) predict an increase of the extreme events which may translate into strong floods in Senegal. As for the dry and wet sequences, the RCMs projections (except those of RCA4) show an increase (respectively a decrease) of the maximum dry spell length (respectively of the maximum wet spell length) in Senegal. This increase in extreme rainfall indices may translate into a strengthening of natural disasters such as floods and drought. This work can be considered as a support for the policymakers in West Africa and particularly in Senegal for the better long-term planning of water resources and disaster management as wells as the build of a resilient agricultural system.

Groundwater monitoring in the archaeological site of Ostia Antica (Rome, Italy): first results

The archaeological site of Ostia Antica hosts the ruins of the ancient roman city called Ostia founded in the VII century B.C. near the mouth of Tiber River. The area was strategically important for Rome, not only for the control of the river, but also for some salt marshes (Ostia Pound). During the XIX century, the whole area was reclaimed and the salt production stopped. Nowadays drainage canals and pumps avoid the flood of zones placed below sea level, keeping dewatering below the ground surface. In February 2014, the site was largely flooded after an exceptional rainfall event and the Superintendence for Archaeological Heritage of Rome ordered the closure for 15 days. Few months later (July 2014) a groundwater monitoring project started with the aim of studying the aquifer response to local rainfall and prevent future damage and groundwater flooding. The activity consisted in water-table monitoring, groundwater electrical conductivity (EC) and temperature continuous measurements, coupled with chemical analysis of major ions. Preliminary results shows the link between water table fluctuations and rainfall distributions. The average elevation of the archaeological area is about 2,5 m a.s.l. and the local water-table depth is of about 0,5 m a.s.l.; groundwater flows from the Tiber River to the reclaimed area according to regional flowpath. Groundwater sampled from three wells is Ca-HCO3 freshwater (600 - 1000 μS/cm), while the sample collected from a well located close to ancient salt storage warehouse (now Ostia Antica museum), is Na-Cl brackish water (about 4000 μS/cm). The chemical evolution of groundwater from summer to winter suggested a possible lateral inflow from the Tiber River, affected by salt-wedge intrusion. The inflow of Ca-Cl, SO4 Tiber’s water with an intermediate salinity could determine salinization of Ca-HCO3 freshwaters and refreshing of Na-Cl brackish water.

Detailed and large-scale cost/benefit analyses of landslide prevention vs. post-event actions

Abstract. The main aim of this paper is to test economic benefits of landslide prevention measures vs. post-event emergency actions. To this end, detailed- and large-scale analyses were performed in a training area located in the northeastern Italian pre-Alps that was hit by an exceptional rainfall event occurred in November 2010. On the detailed scale, a landslide reactivated after 2010 event was investigated. Numerical modeling demonstrated that remedial works carried out after the landslide – water-removal intervention such as a drainage trench – could have improved slope stability if applied before its occurrence. Then, a cost/benefit analysis was employed. It defined that prevention would have been economically convenient compared to a non-preventive and passive attitude, allowing a 30 % saving relative to total costs. On the large scale, one of the most affected areas after 2010 event was considered. A susceptibility analysis was performed using a simple probabilistic model, which allowed to highlight the main landslide conditioning factors and the most hazardous and vulnerable sectors. In particular, such low-cost analysis demonstrated that almost 50 % of landslides occurred after 2010 event could be foreseen and allowed to roughly quantify benefits from regional landslide prevention. However, a large-scale approach is insufficient to carry out a quantitative cost/benefit analysis, for which a detailed case-by-case risk assessment is needed. The here proposed approaches could be used as a means of preventive soil protection in not only the investigated case study but also all those hazardous areas where preventive measures are needed.

Severe soil erosion during a 3-day exceptional rainfall event: combining modelling and field data for a fallow cereal field

Exceptional rainfall events cause significant losses of soil, although few studies have addressed the validation of model predictions at field scale during severe erosive episodes. In this study, we evaluate the predictive ability of the enhanced Soil Erosion and Redistribution Tool (SERT-2014) model for mapping and quantifying soil erosion during the exceptional rainfall event (~235 mm) that affected the Central Spanish Pyrenees in October 2012. The capacity of the simulation model is evaluated in a fallow cereal field (1.9 ha) at a high spatial scale (1 × 1 m). Validation was performed with field-quantified rates of soil loss in the rills and ephemeral gullies and also with a detailed map of soil redistribution. The SERT-2014 model was run for the six rainfall sub-events that made up the exceptional event, simulating the different hydrological responses of soils with maximum runoff depths ranging between 40 and 1017 mm. Predicted average and maximum soil erosion was 11 and 117 Mg ha−1 event−1, respectively. Total soil loss and sediment yield to the La Reina gully amounted to 16.3 and 9.0 Mg event−1. These rates are in agreement with field estimations of soil loss of 20.0 Mg event−1. Most soil loss (86%) occurred during the first sub-event. Although soil accumulation was overestimated in the first sub-event because of the large amount of detached soil, the enhanced SERT-2014 model successfully predicted the different spatial patterns and values of soil redistribution for each sub-event. Further research should focus on stream transport capacity. Copyright © 2014 John Wiley & Sons, Ltd.

Integration between ground based and satellite SAR data in landslide mapping: The San Fratello case study

The potential use of the integration of PSI (Persistent Scatterer Interferometry) and GB-InSAR (Ground-based Synthetic Aperture Radar Interferometry) for landslide hazard mitigation was evaluated for mapping and monitoring activities of the San Fratello landslide (Sicily, Italy). Intense and exceptional rainfall events are the main factors that triggered several slope movements in the study area, which is susceptible to landslides, because of its steep slopes and silty–clayey sedimentary cover.In the last three centuries, the town of San Fratello was affected by three large landslides, developed in different periods: the oldest one occurred in 1754, damaging the northeastern sector of the town; in 1922 a large landslide completely destroyed a wide area in the western hillside of the town. In this paper, the attention is focussed on the most recent landslide that occurred on 14 February 2010: in this case, the phenomenon produced the failure of a large sector of the eastern hillside, causing severe damages to buildings and infrastructures. In particular, several slow-moving rotational and translational slides occurred in the area, making it suitable to monitor ground instability through different InSAR techniques.PS-InSAR™ (permanent scatterers SAR interferometry) techniques, using ERS-1/ERS-2, ENVISAT, RADARSAT-1, and COSMO-SkyMed SAR images, were applied to analyze ground displacements during pre- and post-event phases. Moreover, during the post-event phase in March 2010, a GB-InSAR system, able to acquire data continuously every 14min, was installed collecting ground displacement maps for a period of about three years, until March 2013. Through the integration of space-borne and ground-based data sets, ground deformation velocity maps were obtained, providing a more accurate delimitation of the February 2010 landslide boundary, with respect to the carried out traditional geomorphological field survey. The integration of GB-InSAR and PSI techniques proved to be very effective in landslide mapping in the San Fratello test site, representing a valid scientific support for local authorities and decision makers during the post-emergency management.

GIS APPROACH FOR PREVENTIVE EVALUATION OF ROADS LOSS OF EFFICIENCY IN HYDROGEOLOGICAL EMERGENCIES

Abstract. The theme of the simulation of hydrogeological risk with GIS technology is analyzed with focus on the modeling of the architecture of a Spatial Data Base to support risk analysis and on the construction of a specialized frame with free and open source software. For this purpose a model of analysis of the vulnerability of roads developed by (Cafiso et al., 2002) has been adopted. The case of study is represented by a seismic land characterized by steep slopes and frequent instability phenomena. In detail, the area of interest is a mountainous land in Sicily with a city, Enna (about 30 000 people), that lies on the top. The access to the city is assured by few and very winding roads which are also highly vulnerable to seismic and hydrogeological hazards. The loss of efficiency of these roads for exceptional rainfall events should compromise timeliness and effectiveness of rescue operations. The data of the sample area have been implemented in the specialized GIS appositely constructed in order to forecast the possible damage to roads and the results of some simulations have been related to the effects registered after some extreme events, obtaining useful indications for the validation of the approach.