1,721,025 research outputs found
Tensio-inclinometro: uno strumento wireless a sostegno dei sistemi di early warning per frane meteoindotte
No full textI sistemi di early warning per frane meteo indotte attualmente implementati sono essenzialmente basati sul monitoraggio e l’interpretazione delle precipitazioni. L’accuratezza di tali sistemi, indispensabile per minimizzare mancati e falsi allarmi, può essere migliorata puntando anche al monitoraggio delle variabili effetto delle precipitazioni stesse, ovvero quelle variabili precorritrici del fenomeno di instabilità. Si tratta, in particolare, delle variabili idrologiche (suzione e contenuto d’acqua) che descrivono lo stato dell’imbibizione della coltre e delle variabili cinematiche, che caratterizzano il comportamento deformativo che precede la rottura. A tale scopo è stato migliorato ed ingegnerizzato uno strumento realizzato in precedenza, il tensio-inclinometro, e sono state realizzate alcune prove di validazione dello strumento su modello fisico
Estimating actual and potential bare soil evaporation from silty pyroclastic soils: Towards improved landslide prediction
No full textThe estimation of evaporative fluxes and their effects on soil suction is assuming a prominent role in the field of interpretation and early-warning prediction of rainfall-induced landslides. Evaporation models refer essentially to sands or plastic (silty and clayey) soils. Models validated specifically for non-plastic silty pyroclastic soils, usually characterized by very high porosity, are instead unavailable. This deficit arises although silty pyroclastic covers are widely spread across the world, increasingly involved in rainfall-induced landslides and recognized showing particular hydrological behaviour. A number of questions may be raised about the issue: (i) may any evaporative models be reliably extended to silty pyroclastic soils?; (ii) what atmospheric variables need to be monitored at least to reliably predict evaporation fluxes in these soils?; and (iii) how accurate evaporation estimations are if they are referred to silty pyroclastic covers for early warning purposes? This study addresses these questions by assessing the capabilities of several simplified models in estimating evaporative (potential and actual) fluxes for silty pyroclastic soils. To this aim, a large-scale lysimeter, consisting in a silty pyroclastic layer exposed to the atmosphere and comprehensively monitored for both weather forcing and hydrological soil variables, is adopted. It provides a dataset of observations suitable to calibrate and validate the selected evaporation models. Moreover, the availability of weather observations makes it possible to define the minimum set of equipment required to attain reliable evaporation estimation. This study shows that: (i) the adoption of a literature-based calibration can produce misleading estimates of actual evaporation, whereas the model performances after a lysimeter-based recalibration are satisfactory; (ii) reducing the weather measurements can induce an overestimation of predicted fluxes up to 50%; and (iii) the investigated models quite accurately predict water out-coming fluxes while running in early warning predictions
Effects of vegetation on hydrological response of silty volcanic covers
No full textThis work examines the hydrological behaviour of a silty volcanic layer exposed to the atmosphere for 3 years under vegetated conditions. The layer was extensively monitored to measure energy fluxes, water fluxes, and internal variables
(suction, water content, water storage, and temperature). Measurements were used to build representations of the layer’s
behaviour patterns depending on its surface covering, comparing the behaviour in vegetated conditions with behaviour observed under bare conditions over the previous 4 years. Results show that during cold–dry periods, differences in terms of fluxes
and hydrological variables between the bare and vegetated conditions reduce to negligible levels, but increase significantly
during hot–dry and transition periods. As the soil forming the layer was selected to have the same intrinsic and state properties
as the layer in a specific rainfall-induced landslide case history that occurred in Nocera Inferiore (South Italy) in 2005, the
experimental results are used to re-interpret such a landslide, considering the effects of vegetation and referring to a coupled
thermohydraulic model. The experimental results are used to calibrate the model, and this is then used to interpret around
10 years of meteorological variables recorded at the landslide site, including the landslide time. Comparison with interpretations
made previously as a bare soil hypothesis shows how neglecting the effects of vegetation might imply a loss in prediction
accuracy of soil state variables (suction and water storage) related to the slope stabilit
An ensemble approach for the analysis of extreme rainfall under climate change in Naples (Italy)
No full textIn the present paper, an ensemble approach is proposed to estimate possible modifications caused by climate changes in the extreme precipitation regime, with the rain gauge Napoli Servizio Idrografico (Naples, Italy) chosen as test case. The proposed research, focused on the analysis of extremes on the basis of climate model simulations and rainfall observations, is structured in several consecutive steps. In the first step, all the dynamically downscaled EURO-CORDEX simulations at about 12 km horizontal resolution are collected for the current period 1971–2000 and the future period 2071–2100, for the RCP4.5 and the RCP8.5 concentration scenarios. In the second step, the significance of climate change effects on extreme precipitation is statistically tested by comparing current and future simulated data and bias-correction is performed by means of a novel approach based on a combination of simple delta change and quantile delta mapping, in compliance with the storm index method. In the third step, two different ensemble models are proposed, accounting for the variabilities given by the use of different climate models and for their hindcast performances. Finally, the ensemble models are used to build novel intensity–duration–frequency curves, and their effects on the early warning system thresholds for the area of interest are evaluated
From empirically to physically based early warning predictions of rainfall-induced landslides in silty volcanic soils: the Lattari Mountains case study
Full text linkThe work proposes a procedure to build an early warning predictive tool to assess the occurrence of rainfall-induced landslides in silty volcanic covers. The procedure combines both an empirically and a physically based tool used sequentially: the former is designed to be calibrated using older, highly sized and coarser rainfall data, and the latter to interpret recent and finer weather data. Both approaches need to be informed by a common experimental reference summarising the rainfall history, the rainfall point, defined as the couple made of antecedent 4-month rainfall cumulative value (C-4m) and last-persistent event (C-PLE). The empirical approach aims to identify if, in the (C-4m-C-PLE) plane, the rainfall point falls in a 'safe' or 'potentially unsafe' zone where the two distinct regions are built by interpreting rainfall data associated or not with landslide events. In the physically based approach, evaporation and runoff are estimated to refine the assessment of 'effective' rainfall points. The resulting transformed rainfall point (C '(4 m), C '(PLE)) is turned into a prediction of the suction level at the mid-depth assumed as a 'reference' for the entire cover. Such value is compared with a suction threshold empirically defined. Suction levels prediction is developed by computing in the C '(4 m)-C '(PLE) plane the iso-suction lines generated by several rainfall scenarios. The accuracy of the developed procedure is comparable with state-of-the-art literature or operational approaches, properly identifying landslide case events and minimising the number of false alarms. Furthermore, it can inform the preparedness stages more effectively, explicitly accounting for the antecedent slope wetness stage and how it could be far from the incipient slope failure conditions. The developed procedure takes into account the effects of evaporation and antecedent rainfalls that, in dry periods, lead to very dry conditions in the subsoil, making even significant rainfall events inconsequential. Conversely, other procedures already operating in LEWS or highly considered literature background overestimate the effects of rainfalls during dry periods. The developed procedure delivers a simple but robust way to derive landslide thresholds based on the interpretation of past rainfall histories. At the same time, literature methods often require sophisticated approaches to retrieve thresholds
Tensio-Inclinometer: A Deployable Wireless Device to Underpin Early Warning Systems for Rainfall-Induced Shallow Landslides
No full textMost of the Landslides Early Warning Systems (LEWS) currently in operation are based on monitoring rainfall data only. This feature limits their performance due to false alarms generated by rainfall thresholds inevitably conservative. The accuracy of LEWS may be significantly enhanced by monitoring soil-based variables associated with the stress-strain response of the ground. The paper presents a novel Tensio-inclinometer specifically developed to measure suction changes and suction-induced deformation in shallow covers. The device is made of a MEMS accelerometer mounted on the shaft of a commercial tensiometer. On-board electronics and battery-based power supply make the device fully wireless. The Tensio-inclinometer is therefore easy to deploy and install allowing the design of a flexible and adaptive monitoring network to underpin early-warning systems. The device was tested in a slope physical model where instability of a shallow silt layer was triggered by artificial rainfall. It is shown that pre-failure deformation, as detected by the tilting of the tensiometer shaft, is an adequate landslide precursor and that combined suction and rotation measurements can provide soil-based thresholds for early warning systems
A simplified procedure to assess the effects of climate change on landslide hazard in a small area of the Southern Apennines in Italy
No full textSeveral impacts of climate change are becoming evident and will be more and more apparent in the future. The threats and challenges posed by weather patterns variations can change according to the variables of interest, geography, and socio-economic contexts. At the moment, we are compelled to assess their impacts, so as to identify priorities and devise effective countermeasures. A major concern is that of geo-hydrological risks, including the potential effects of landslide evolution in unstable areas. Based on available data on the relationship between soil-atmosphere interaction and mobility of a slow active earthflow in Southern Italy, the paper tries to correlate the expected future precipitation potential evapotranspiration balance and the water level fluctuations that govern landslide mobility. The investigation is carried out in the framework of the bottom-up approach known as decision scaling, which lets us evaluate landslide dynamics sensitivity to the variations in soil water budget by means of a simple abacus. Such a tool will make it possible to obtain fast updates on assessing landslide trends when new generations of climate projections become available
A simplified procedure to assess the effects of climate change on landslide hazard in a small area of the Southern Apennines in Italy
No full textAbstract
Several impacts of climate change are becoming evident and will be more and more appar ent in the future. The threats and challenges posed by weather patterns variations can
change according to the variables of interest, geography, and socio-economic contexts. At
the moment, we are compelled to assess their impacts, so as to identify priorities and devise
efective countermeasures. A major concern is that of geo-hydrological risks, including the
potential efects of landslide evolution in unstable areas. Based on available data on the
relationship between soil–atmosphere interaction and mobility of a slow active earthfow in
Southern Italy, the paper tries to correlate the expected future precipitation potential evapo transpiration balance and the water level fuctuations that govern landslide mobility. The
investigation is carried out in the framework of the bottom-up approach known as deci sion scaling, which lets us evaluate landslide dynamics sensitivity to the variations in soil
water budget by means of a simple abacus. Such a tool will make it possible to obtain fast
updates on assessing landslide trends when new generations of climate projections become
availabl
Effects of Wooden Embers Cover on thermo-hydrological response of silty volcanic cover and implications to post-wildfire slope stability
No full textWildfires striking vegetated hillslopes appear to increase the hazard towards rainfall-induced landslides. One mechanism little investigated in the literature consists in the formation of Wooden Embers Cover (WEC) following the wildfire. This layer has very peculiar thermohydraulic properties and may affect the interaction between the atmosphere and the subsoil. The paper presents an experiment conducted in an outdoor lysimeter filled with pyroclastic silt (SILT) up to 75 cm covered with 5 cm of WEC. Water storage in the SILT layer, soil water content, suction, and temperature were recorded for several years, initially under bare (no-WEC) condition (4 years), then vegetated (no-WEC) condition (5 years) and, finally, with a WEC placed on the top of the SILT (SILT+WEC condition; 3 years). The hydrological effect of the WEC was assessed by comparing the response of the SILT+WEC with the SILT under bare or vegetated conditions. The WEC reduces water losses by evaporation, thus increasing the average water content in the underlying SILT, an effect that is detrimental to slope stability. To discriminate whether the barrier effect was associated with the lower thermal or hydraulic conductivity of the WEC, a numerical simulation was carried out by considering the case of a WEC with its real thermal and hydraulic properties and the case of a fictitious top layer placed on the top of the SILT having the same hydraulic properties of the WEC but the thermal properties of the SILT. It is concluded that the barrier effect of the WEC is mainly associated with its hydraulic properties, i.e. the WEC acts as a capillary barrier. To demonstrate the practical implications of this findings, a case study of rainfall-induced landslide has been reanalysed by simulating the presence of a WEC layer having the same thermohydraulic properties as the material characterised in this study. It is shown that a WEC can substantially reduce the severity of the triggering rainfall event, thus increasing the vulnerability of the slope to rainfall-induced failur
Characterizing extreme values of precipitation at very high resolution: An experiment over twenty European cities
Full text linkThe paper presents a new hourly high-resolution (i.e., at 0.02°, ≃2.2 km) precipitation dataset, labelled as ERA5@2km, obtained by dynamically downscaling ERA5 reanalysis at convection permitting scale (CPS) over 20 European cities for the recent past thirty years (1989–2018). The downscaling activity is performed within the framework of the Contract implemented by Fondazione CMCC to support Sectoral Information System about “Disaster Risk Reduction” (see https://climate.copernicus.eu/pluvial-flood-risk-assessment-urban-areas) of Copernicus Climate Change Service (C3S). Specifically, such an additional precipitation dataset is developed to provide precipitation data for estimating expected precipitations at fixed return periods used as input for pluvial flooding risk analysis where hazard (inundated areas, water levels) and risk (estimated damages) are assessed. The ambition is to support the Disaster Risk Reduction (DRR) community involved in pluvial flood risk assessment by providing a basis for impact analysis at city scale, in terms of extreme hourly precipitation, that matches with the expected spatial and temporal requirements. In this work, ERA5@2km precipitation dataset is introduced for the first time and its reliability and coherence are evaluated as for spatial patterns and trends as for extreme values against a set of available high-resolution observational datasets (comparable in terms of spatial and temporal resolution). Such an evaluation provides a clearer understanding about the added value of very high-resolution (VHR) dynamical downscaling reanalysis in terms of localization and magnitude of precipitation events at urban scale, confirming a general and relevant added value of this new configuration for the assessment of extreme atmospheric events (such as heavy precipitations)
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