On the 4th and 5th of March 2005, about 100 rainfall-induced landslides occurred along volcanic slopes of Camaldoli Hill in Naples, Italy. These started as soil slips in the upper substratum of incoherent and welded volcaniclastic deposits, then evolved downslope according to debris avalanche and debris flow mechanisms. This specific case of slope instability on complex volcaniclastic deposits remains poorly characterized and understood, although similar shallow landsliding phenomena have largely been studied in other peri-volcanic areas of the Campania region underlain by carbonate bedrock. Considering the landslide hazard in this urbanized area, this study focused on quantitatively advancing the understanding of the predisposing factors and hydrological conditions contributing to the initial landslide triggering. Borehole drilling, trial pits, dynamic penetrometer tests, topographic surveys, and infiltration tests were conducted on a slope sector of Camaldoli Hill to develop a geological framework model. Undisturbed soil samples were collected for laboratory testing to further characterize hydraulic and geotechnical properties of the soil units identified. In situ soil pressure head monitoring probes were also installed. A numerical model of two-dimensional variably saturated subsurface water flow was parameterized for the monitored hillslope using field and laboratory data. Based on the observed soil pressure head dynamics, the model was calibrated by adjusting the evapotranspiration parameters. This physically based hydrologic model was combined with an infinite-slope stability analysis to reconstruct the critical unsaturated/saturated conditions leading to slope failure. This coupled hydromechanical numerical model was then used to determine intensity–duration (I-D) thresholds for landslide initiation over a range of plausible rainfall intensities and topographic slope angles for the region. The proposed approach can be conceived as a practicable method for defining a warning criterion in urbanized areas threatened by rainfall-induced shallow landslides, given the unavailability of a consistent inventory of past landslide events that prevents a rigorous empirical analysis.

Incorporating the influence of soil layering and local variability into the parameterizations of physics-based numerical models for distributed landslide susceptibility assessments remains a challenge. Typical applications employ substantial simplifications including homogeneous soil units and soil-hydraulic properties assigned based only on average textural classifications; the potential impact of these assumptions is usually disregarded. We present a multi-scale approach for parameterizing the distributed Transient Rainfall Infiltration and Grid-Based Regional Slope-Stability (TRIGRS) model that accounts for site-specific spatial variations in both soil thickness and complex layering properties by defining homogeneous soil properties that vary spatially for each model grid cell. These effective properties allow TRIGRS to accurately simulate the timing and distribution of slope failures without any modification of the model structure. We implemented this approach for the carbonate ridge of Sarno Mountains (southern Italy) whose slopes are mantled by complex layered soils of pyroclastic origin. The urbanized foot slopes enveloping these mountains are among the most landslide-prone areas of Italy and have been subjected to repeated occurrences of damaging and deadly rainfall-induced flow-type shallow landslides. At this scope, a primary local-scale application of TRIGRS was calibrated on physics-based rainfall thresholds, previously determined by a coupled VS2D (version 1.3) hydrological modeling and slope stability analysis. Subsequently, by taking into account the spatial distribution of soil thickness and vertical heterogeneity of soil hydrological and mechanical properties, a distributed assessment of landslide hazard was carried out by means of TRIGRS. The combination of these approaches led to the spatial assessment of landslide hazard under different hypothetical rainfall intensities and antecedent hydrological conditions. This approach to parameterizing TRIGRS can be adapted to other spatially variable soil layering and thickness to improve hazard assessments.

In many Italian regions, and particularly in southern Italy, karst aquifers are the main sources of drinking water and play a crucial role in the socio-economic development of the territory. Hence, estimating the groundwater recharge of these aquifers is a fundamental task for the proper management of water resources, while also considering the impacts of climate changes. In the southern Apennines, the assessment of hydrological parameters that is needed for the estimation of groundwater recharge is a challenging issue, especially for the spatial and temporal inhomogeneity of networks of rain and air temperature stations, as well as the variable geomorphological features and land use across mountainous karst areas. In such a framework, the integration of terrestrial and remotely sensed data is a promising approach to limit these uncertainties. In this research, estimations of actual evapotranspiration and groundwater recharge using remotely sensed data gathered by the Moderate Resolution Imaging Spectrometer (MODIS) satellite in the period 2000–2014 are shown for karst aquifers of the southern Apennines. To assess the uncertainties affecting conventional methods based on empirical formulas, the values estimated by the MODIS dataset were compared with those calculated by Coutagne, Turc, and Thornthwaite classical empirical formulas, which were based on the recordings of meteorological stations. The annual rainfall time series of 266 rain gauges and 150 air temperature stations, recorded using meteorological networks managed by public agencies in the period 2000–2014, were considered for reconstructing the regional distributed models of actual evapotranspiration (AET) and groundwater recharge. Considering the MODIS AET, the mean annual groundwater recharge for karst aquifers was estimated to be about 448 mm·year⁻¹. In contrast, using the Turc, Coutagne, and Thornthwaite methods, it was estimated as being 494, 533, and 437 mm·year⁻¹, respectively. The obtained results open a new methodological perspective for the assessment of the groundwater recharge of karst aquifers at the regional and mean annual scales, allowing for limiting uncertainties and taking into account a spatial resolution greater than that of the existing meteorological networks. Among the most relevant results obtained via the comparison of classical approaches used for estimating evapotranspiration is the good matching of the actual evapotranspiration estimated using MODIS data with the potential evapotranspiration estimated using the Thornthwaite formula. This result was considered linked to the availability of soil moisture for the evapotranspiration demand due to the relevant precipitation in the area, the general occurrence of soils covering karst aquifers, and the dense vegetation.

Archeological sites close to coastal volcanic-sedimentary aquifers are threatened by groundwater contaminated by natural and anthropogenic processes. The paper reports on a hydrogeological, chemical (major, minor and trace elements) and isotopic (δD-H₂O, δ¹⁸O-H₂O, δ¹⁵N-NO₃, δ¹⁸O-NO₃, δ¹¹B, ²²²Rn) survey of groundwater at the Cumae archaeological site, which is located in the coastal north-western sector of the volcanic district of Phlegraean Fields (southern Italy), where groundwater flooding phenomena occur. Results show the presence of a complex coastal volcanic-sedimentary aquifer system where groundwater quality is influenced mainly by: (i) aquifer lithology and localized ascent of magmatic fluids along buried volcano-tectonic discontinuities, (ii) mixing of groundwater, deep mineralized fluids and seawater during groundwater pumping, and (iii) nitrate contamination >50 mg/L from non-point agricultural sources. Moreover, δD and δ¹⁸O point toward fast recharge from seasonal precipitations, while the isotopic ratios of N and O in nitrate reveal the contribution of mineral and organic fertilizers as well as leakage from septic tanks. Results can assist the local archaeological authority for the safeguarding and management of the archaeological heritage of the Cumae site.

Aquifer mismanagement is a common anthropogenic cause of subsidence and uplift phenomena in alluvial plains, representing one of the main natural hazards in urban areas due to related damage to urban structures and infrastructures. In this work, the groundwater rebound phenomenon that occurred in the last decades of the 20th century in the Lufrano area (Metropolitan area of Naples, Southern Italy) has been studied by integrating geological data, hydrogeological continuous monitoring and spaceborne SAR information derived from ERS-1/2 and ENVISAT satellites. In the period of 1989–2006, the Lufrano area, which hosts an important well field made up of 180 wells extracting groundwater for drinking use, suffered an initial over-exploitation of the aquifer which was followed by a sudden and severe decrease of the volume abstraction, resulting this last in a rapid ground uplift. The coupled analysis of hydrogeological and DInSAR data have shown a correspondence between piezometric level rise (up to 15 m) and ground uplift (up to 50 mm) trends in the period 1989–2006. In order to examine the spatio-temporal evolution of the phenomena and the cause-effect relationships, showing the link between the two phenomena and their rates, longitudinal cross-sections were carried out and comparisons between piezometric level rise and time-series of displacements were reconstructed. The obtained results represent an initial contribution to the definition of ground deformation related to groundwater level rise phenomena, providing a basis for future studies focused on the modelling of the hydro-mechanical properties of the aquifer.