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Changes in groundwater flow in response to strong earthquakes are widely described in many tectonic environments. For example, a post-seismic discharge variation is often attributed to an increase of bulk permeability due to co-seismic fracturing and/or to a change in the role of faults in acting as conduits/barrier to groundwater flow.We take as an example the fractured aquifer of the Mts. Sibillini carbonate massif, in Central Italy, which were affected by a strong and prolonged extensional seismic sequence in 2016-17. The sequence was characterized by an M=6.5 event (mainshock), an M=6 event, an M=5.9 event, up to 60 M>4 events and several M>5 earthquakes. The strongest events caused rupturing of the topographic surface for a cumulative length in the order of 30 km and an important portion of aftershocks occurred at depths where groundwater is stored.As a response to the seismic sequence, the main NNW-directed groundwater flow was diverted to the west and a discharge deficit was observed at the foot-wall of the activated fault system with a relevant discharge increase, accompanied by geochemical variations, at the fault system hanging-wall.By integrating geo-structural reconstructions, seismological and ground deformation data, artificial tracer tests results and a 4-years discharge and geochemical monitoring campaign data, we show that the observed groundwater variations are due to a combination of permeability increase along the activated fault systems and hydraulic conductivity increase of the hanging-wall block due to fracturing, extension and subsidence, which determined a fast aquifers emptying. Seismicity temporarily triggered a change of the pre-existing predominant along-faults-strike NNW-SSE oriented regional flow to a west-directed flow, perpendicular to faults strike. We discuss the position of the aquifer with respect to the activated faults and how this affected the observed phenomena. REFERENCECambi, C., Mirabella, F., Petitta, M., Banzato, F., Beddini, G., Cardellini, C., ... & Valigi, D. (2022). Reaction of the carbonate Sibillini Mountains Basal aquifer (Central Italy) to the extensional 2016–2017 seismic sequence. Scientific Reports, 12(1), 1-13. DOI: 10.1038/s41598-022-26681-2

Understanding hydrological flow pathways and spatio-temporal origin of surface and subsurface water in catchments with highly fractured geology is particularly challenging. In this work, we relied on the integration of hydrometric measurements with stable oxygen and hydrogen isotope data in two adjacent catchments in the Sibillini Mountains National Park, Central Italy, to better understand the drivers of the catchment hydrological response and the spatio-temporal origin of stream and spring waters. The Ussita catchment is 44 km2 and its highest elevation is 2204 m a.s.l. The Nera catchment is 110 km2 and its highest peak is 2233 m a.s.l. The two rivers merge at the Visso Village, at 615 m a.s.l.The area is characterised by heavily fissured and fractured calcareous rocks that foster the occurrence of several springs, some of them of karst origin. Both catchments host a dense hydrometerological network. The experimental apparatus is completed with one piezometer, soil moisture probes at five locations, lysimeters at two depths and four throughfall plots under beeches and oaks. Monthly samples for isotopic analysis are being collected since fall 2020 from precipitation at three different elevations and four locations, the streams at different sections, and four springs in the Nera catchment only.Preliminary results show a distinct hydrological behaviour in the annual streamflow regimes: the Ussita stream slightly reacts only to the largest storms and during intense snowmelt periods, whereas the Nera stream has a very damped response during all the year, revealing a clear buffer effect of the large subsurface reservoir, facilitated by the highly fractured nature of the geological setting. As expected, there is an elevation and seasonal effect in the isotopic composition of precipitation, although the seasonal effect is partly masked by the exceptionally high temperatures occurred in fall 2021. However, the time series of isotope data in stream water show a damped signal and very low seasonal variability in both streams, matching the observed low variability of streamflow. Only the Ussita catchment shows some more enriched outliers likely reflecting runoff response during large storm events. Interestingly, stream and spring samples from both catchments lie along but also above and below the Local Meteoric Water Line, suggesting that the sampled spring and stream water was either originated i) from precipitation fell, infiltrated, and stored well before the collection of the precipitation samples, and released; ii) and/or from areas outside the topographic catchments, and therefore not adequately characterized by the isotopic signal of sampled precipitation. The isotopic composition of the streams and springs is statistically the same, revealing that spring groundwater is the main component of stream runoff. Moreover, the isotope signature of both springs and streams is much closer to that of winter precipitation rather than summer precipitation indicating a major role of winter precipitation in recharging the catchments, consistently with the precipitation seasonal regime. On-going work is assessing the spatial difference in the isotopic composition and quantifying the temporal origin of stream and spring water of the two catchments.

Over the years the scientific community underlined several problems related to the use of isotopic hydrology techniques in areas characterized by a complex orography, usually occurring in mountain areas, or in those cases where the hydrological setting is complicated by contacts between different aquifers (Nanni et al., 2013).In this study, an innovative isotopic model, able to identify the most probable recharge area for several springs exploited for drinking purposes, has been developed and applied to the Nera catchment in the Sibillini Mountain National Park (central Italy). The isotopic investigation consists of a preliminary definition of a new δ18O - elevation relationship, considering the morphological and meteorological heterogeneities within the area and their possible influences on the precipitation isotope values (e.g., shaded areas, snow drift effect, etc.). Second, an advanced δ18O distribution model, supported by statistical and GIS-based procedures, has been implemented by clipping the precipitation δ18O values (depicted from the δ18O – elevation relationship) over an upstream area for each analyzed spring. The new isotopic modeling approach can be conveniently applied if the infiltration rate of the meteoric water is fast enough to avoid fractionation processes that may alter the isotopic signal of the precipitation input within the aquifer, and if peculiar meteoric recharge phenomena, altering the springs' isotopic signal, are treated as outliers.This research highlights if the most used isotopic approach based on the determination of groundwater recharge areas starting from δ18O - elevation gradient (Jeelani et al., 2010; Jasechko, 2019) applied to a selected spring isotopic data agrees with the hydrogeological setting of the spring recharge area which is often complicated by the topography and the contacts between different aquifers both for stratigraphic and tectonic reasons.The ultimate goal of this study is to quantify the aquifers recharge under the impact of drought to improve the water resources management operations in the area.

In the framework of landslides, the hydrogeological features play an essential role in slope stability, governing water movement and thus resulting in modification of the effective stress in the soil. In this framework, the hydrogeological conceptualization of landslide areas and the identification of groundwater origin are key points to developing risk mitigation measures. In fact, groundwater recharge cannot always be attributed to local precipitation alone. Mixing processes between water derived from local infiltration and deep water upflow along tectonic lineaments or anthropogenic water can affect the groundwater balance on a local scale. This study aims to define the potential groundwater origin of one of the highest risk urban landslides in central Italy and to define a hydrogeological conceptual model by exploiting its existing drainage system network. This research is based on a multiple-techniques approach based on hydrological water balance, artificial tracer tests during recharge period, seasonal monitoring of the water stable-isotope content, hydro-chemical survey during low-flow periods, and analysis of the piezometric level fluctuation. All these analyses are coupled with a detailed reconstruction of the geology of the area depicted from boreholes and drill holes. Two groundwater bodies have been evidenced from the study. The shallower one is located in the landslide unstable zone and is hydraulically connected to a deeper groundwater body hosted in the underlying bedrock. Results highlighted that the local rainfall regime could not fully explain the hydro-chemical facies. Local water contributions to the landslide area coming from leakage of the urban sewerage system have been evidenced, excluding deep groundwater upflow from the fault system.

Placed at the center of the Mediterranean, the Apennines chains provide a critical water supply for people living in the Italian Peninsula. Yet, the quantification of water resources in this region is challenging given that the different components of the water cycles (i.e., snowmelt, evapotranspiration, and subsurface water recharge) are highly variable in space and time due to the specificity of the climate, the reforestation trend, and the complex landscapes and geology. In this study, we investigated the challenging hydrological river regime of a complex carbonate basin with significant external (and partially karst) groundwater contribution – the Upper Nera basin – affected by recent important seismic sequences. When dealing with such type of basins, the generic approach to delineate the basin boundaries based on the geomorphology of the area can lead to questionable results potentially yielding significant water budget imbalances. Therefore, both (hydro)geological and hydrological features have to be considered for understanding the challenging hydrological behavior of these basins. Here we proposed a specific analysis of precipitation-runoff time series corroborated with hydro-geological survey to obtain information on the basin response time and the real contribution area of the basin. Then, we integrated this information within the structure of a hydrological model (i.e., the Geoframe modelling system) by using a parsimonious type of approach to improve the description of the different components of the water balance with a specific focus on external groundwater recharge. We validated the model against in situ discharge observations and with remote sensing information of evapotranspiration and snow. Since these two variables (snow cover and evapotranspiration) play the crucial role in correct estimation of water balance in the basin, in this study we additionally focused on that. We show that the model (tested with several hydrological signatures and a new conceptual evaluation based on an empirical probability function) performs relatively well in reproducing the different water balance components (including remotely sensed evapotranspiration and snow) and that the upper river basin is significantly impacted by carbonate rock river discharge (i.e., up to 85 % in proportion to the total discharge for some stations) coming from outside the geomorphological boundary of the basin. Yet, the groundwater recharge effects on the river, gradually attenuates at the outlet of the basin (Visso station).

The analysis of the water budget in the Upper Nera River basin, typical karst and fissured rocks catchment located in the Apennines chains in central Italy, has been performed to simulate snow, Evapotranspiration (ET), and runoff through different components of the GEOframe system. During this study, we showed that using an unsupervised approach for extracting the basin boundary could provide significant issues in the correct estimation of water budget components. To overcome this problem, both hydrogeological and hydrological information -obtained through a new type of time-series analyses and recent geological surveys- have been considered to estimate the contribution area and time response of the karst discharge. According to the mentioned information and benefiting the flexibility of the GEOframe-NewAge modeling system, a conceptual reservoir with a 30-day time response, derived from the time series analysis, has been added to estimate the karst river discharge contributed to Nera. The model, evaluated by different signatures (including mean daily discharge, high flow, low flow, low flow duration frequency, and flow duration curve slope and a new empirical probability function) has been shown to reproduce the water fluxes of the hydrological cycle in the basin relatively well (KGE values equal to 0.61, 0.80, and 0.71 in different sections, respectively). The karst discharge flux has a significant effect on the water budget of the basin especially in the upstream part (Castelsantangelo section) and this effect decreased through the river downstream to the outlet of Visso. We showed that 85% of the total discharge at Castelsantangelo station comes from outside of the geomorphological boundary of the basin. According to the water balance analysis, the maximum karst flux that happened in 2014 could be mainly caused by the maximum precipitation that happened in 2013 over the basin. To further cross-validation of the model performance, MODIS ET and Sentinel-1 snow depth products were used. The comparison of remote-sensed MODIS ET and GEOframe ET shows a systematic difference, with higher values of MODIS ET than our model estimations. As well, the spatial correlation of snow cover retrieved from Sentinel-1 snow depth and GEOframe Snow Water Equivalent has been examined and a good correlation has been reported especially for Castelsantangelo. The values of Sentinel-1 were also verified through some in-situ snow depth data.

The interaction between fluids and tectonic structures such as fault systems is a much-discussed issue. Many scientific works are aimed at understanding what the role of fault systems in the displacement of deep fluids is, by investigating the interaction between the upper mantle, the lower crustal portion and the upraising of gasses carried by liquids. Many other scientific works try to explore the interaction between the recharge processes, i.e., precipitation, and the fault zones, aiming to recognize the function of the abovementioned structures and their capability to direct groundwater flow towards preferential drainage areas. Understanding the role of faults in the recharge processes of punctual and linear springs, meant as gaining streams, is a key point in hydrogeology, as it is known that faults can act either as flow barriers or as preferential flow paths. In this work an investigation of a fault system located in the Nera River catchment (Italy), based on geo-structural investigations, tracer tests, geochemical and isotopic recharge modelling, allows to identify the role of the normal fault system before and after the 2016–2017 central Italy seismic sequence (Mmax = 6.5). The outcome was achieved by an integrated approach consisting of a structural geology field work, combined with GIS-based analysis, and of a hydrogeological investigation based on artificial tracer tests and geochemical and isotopic analyses.

Nowadays, the balance between incoming precipitation and stream or spring discharge is a challenging aspect in many scientific disciplines related to water management. In this regard, although advances in the methodologies for water balance calculation concerning each component of the water cycle have been achieved, the Thornthwaite–Mather method remains one of the most used, especially for hydrogeological purposes. In fact, in contrast to physical-based models, which require many input parameters, the Thornthwaite–Mather method is a simple, empirical, data-driven procedure in which the error associated with its use is smaller than that associated with the measurement of input data. The disadvantage of this method is that elaboration times can be excessively long if a classical MS Excel file is used for a large amount of data. Although many authors have attempted to automatize the procedure using simple algorithms or graphical user interfaces, some bugs have been detected. For these reasons, we propose a WebApp for monthly water balance calculation, called WaterbalANce. WaterbalANce was written in Python and is driven by a serverless computing approach. Two respective European watersheds are selected and presented to demonstrate the application of this method.

A large tank (1.4 m x 4.0 m x 1.3 m) filled with medium-coarse sand was employed to measure evaporation rates from shallow groundwater at controlled laboratory conditions, to determine drivers and mechanisms. To monitor the groundwater level drawdown 12 piezometers were installed in a semi regular grid and equipped with high precision water level, temperature, and electrical conductivity (EC) probes. In each piezometer, 6 micro sampling ports were installed every 10 cm to capture vertical salinity gradients. Moreover, the soil water content, temperature and EC were measured in the unsaturated zone using TDR probes placed at 5, 20 and 40 cm depth. The monitoring started in February 2020 and lasted for 4 months until the groundwater drawdown became residual. To model the groundwater heads, temperature, and salinity variations SEAWAT 4.0 was employed. The calibrated model was then used to obtain the unknown parameters, such as: maximum evaporation rates (1.5-4.4 mm/d), extinction depth (0.90 m), mineral dissolution (5.0e-9 g/d) and evaporation concentration (0.35 g/L). Despite the drawdown was uniformly distributed, the increase of groundwater salinity was rather uneven, while the temperature increase mimicked the atmospheric temperature increase. The initial groundwater salinity and the small changes in the evaporation rate controlled the evapoconcentration process in groundwater, while the effective porosity was the most sensitive parameter. This study demonstrates that shallow groundwater evaporation from sandy soils can produce homogeneous water table drawdown but appreciable differences in the distribution of groundwater salinity.

This study wants to give a contribution to the semi-automatic evaluation of rock mass discontinuities, orientation and spacing, as important parameters used in Engineering. In complex and inaccessible study areas, a traditional geological survey is hard to conduct, therefore, remote sensing techniques have proven to be a very useful tool for discontinuity analysis. However, critical expert judgment is necessary to make reliable analyses. For this reason, the open-source Python tool named DCS (Discontinuities Classification and Spacing) was developed to manage point cloud data. The tool is written in Python and is based on semi-supervised clustering. By this approach the users can: (a) estimate the number of discontinuity sets (here referred to as “clusters”) using the Error Sum of Squares (SSE) method and the K-means algorithm; (b) evaluate step by step the quality of the classification visualizing the stereonet and the scatterplot of dip vs. dip direction from the clustering; (c) supervise the clustering procedure through a manual initialization of centroids; (d) calculate the normal spacing. In contrast to other algorithms available in the literature, the DCS method does not require complex parameters as inputs for the classification and permits the users to supervise the procedure at each step. The DCS approach was tested on the steep coastal cliff of Ancona town (Italy), called the Cardeto–Passetto cliff, which is characterized by a complex fracturing and is largely affected by rockfall phenomena. The results of discontinuity orientation were validated with the field survey and compared with the ones of the FACETS plug-in of CloudCompare. In addition, the algorithm was tested and validated on regular surfaces of an anthropic wall located at the bottom of the cliff. Eventually, a kinematic analysis of rock slope stability was performed, discussing the advantages and limitations of the methods considered and making fundamental considerations on their use.

Understanding the groundwater flow in carbonate aquifers represents a challenging aspect in hydrogeology, especially when they have been struck by strong seismic events. It has been proved that large earthquakes change springs hydrodynamic behaviour showing transitory or long-lasting variations and making their management much more difficult. This is the case of Sibillini Massif (central Italy), which has been hit by the well-known 2016&ndash, 2017 seismic period. This work aims to improve the knowledge of carbonate aquifers groundwater circulation and their possible changes in the hydrodynamic behaviour, during and after a series of strong seismic events. The goal has been achieved by comparing long-time tracer tests and transient time-series analysis, based on a sliding-window approach. This approach allowed investigating transient variations in the carbonate aquifers recharge system, highlighting the changes of relationships between the inflow contributions to the spring discharge in the area. As a result, the seismically triggered pore pressure distribution, and the hydraulic conductivity variations, because of the ground shaking and the fault systems activation, account for all the mid- and long-term modifications in the recharge system of Sibillini aquifers, respectively. These outcomes provide valuable insights to the knowledge of aquifer response under similar hydrogeological conditions, that are vital for water management.

The dynamic of groundwater systems feeding several springs of the Sibillini Mountains was deeply affected by nine Mw 5.0÷6.5 seismic events occurred in central Italy starting from August 2016. The strongest shock occurred on October 30th 2016 about 5 km NNE of Norcia Town, 9 km below the surface, as a result of upper crust normal faulting on the nearly 30 km-long Mt Vettore - Mt Bove fault system, a NW-SE trending, SW-dipping fault system outcropping on the western slope of Mt Vettore, the highest peak of Sibillini Mountains. Soon after this event, a general increase of springs and rivers discharge and groundwater levels was observed both in the Visso and Norcia areas, west of the Sibillini Mountains. In the Visso area the hydrogeological changes due to the seismic sequence exhausted in the 2019, while nowadays both discharges and groundwater levels are still higher than before in the Norcia area. Discharge data of the main springs located east, south-east of the Sibillini Mountains were analysed to verify whether the general increase observed on the western side was associated to a decrease on the eastern and southern-east area. The results show that the springs located on the eastern side and southern-east side of Mt Vettore experienced a significant long-term discharge decrease. In this preliminary work, the analysis of the historical discharge series of the Pescara di Arquata spring (SE of Mt Vettore), and its relationship with the Standard Precipitation Index (SPI) shows that the very low discharge values recorded during the post-seismic period are not associated with SPI as low as documented in the past for similar discharges. Moreover, the stable isotopic composition of Pescara di Arquata water during the post-earthquake period is slightly different from that measured before the seismic events; this suggests that a lower amount of water having more enriched isotopic δ18O content reaches the spring after the seismic sequence. These aspects seem to indicate that groundwater circulation in the southern-east area of Sibillini Mountains has been affected by the 2016-2017 seismic sequence.

The Soil and Water Assessment Tool (SWAT) is a physical model designed to predict the hydrological processes that could characterize natural and anthropized watersheds. The model can be forced using input data of climate prediction models, soil characteristics and land use scenarios to forecast their effect on hydrological processes. In this study, the SWAT model has been applied in the Aspio basin, a small watershed, highly anthropized and characterized by a short runoff generation. Three simulations setup, named SL1, SL2 and SL3, were investigated using different soil resolution to identify the best model performance. An increase of space requirement and calibration time has been registered in conjunction with the increasing soil resolution. Among all simulations, SL1 has been chosen as the best one in describing watershed streamflow, despite it was characterized by the lower soil resolution. A map of susceptibility to runoff for the entire basin was so created reclassifying the runoff amount of four years in five classes of susceptibility, from very low to very high. Eleven sub-basins, coinciding with the main urban settlements, were identified as highly susceptible to runoff generation. Considering future climate predictions, a slight increase of runoff has been forecasted during summer and autumn. The map of susceptibility successfully identified as highly prone to runoff those sub-basins where extreme flood events were yet recorded in the past, remarking the reliability of the proposed assessment and suggesting that this methodology could represent a useful tool in flood managing plan.

Co-seismic changes in groundwater regime are often observed after moderate to strong earthquakes. The 24 August 2016 Mw 6.0 extensional Amatrice earthquake, which was the first event of a long-lasting seismic sequence, including the 30 October 2016 Mw 6.5 Norcia event, triggered a significant discharge alteration to the Pescara di Arquata spring, located in the Umbria-Marche Apennines (Northern Apennines, Central Italy) and exploited for drinking purposes. During the first five months after the first mainshock, an extra flow of about 30% was recorded, while both water chemistry and temperature did not show significant changes. Thereafter, the spring discharge decreased significantly, and at the end of 2019 it was still lower than normal. The Standardized Precipitation Index (SPI) indicates that these low mean monthly discharge values are not related to particularly dry conditions. The increase in post-seismic depletion coefficients indicates that the aquifer empties faster than it did during the inter-seismic period. The observed transient increase and subsequent decrease of discharge are consistent with a transient, earthquake-related increase in hydraulic conductivity.