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Mountainous zones are often characterized by complex orography and contacts between different aquifers that usually complicate the use of isotope hydrology techniques. The Apennine chain (Italy) and 10 mountain and mid‐mountain areas belonging to it are the objective of this study. An original isotopic data treatment, able to identify the most probable recharge area for several springs/springs' groups/wells, has been developed. The method consists of a two‐step approach: (1) the determination of the spring/wells computed isotope recharge elevation; (2) an advanced δ18O precipitation distribution model over the study area supported by statistical and GIS‐based procedures implemented by two processes: first, the clipping of precipitation δ18O values (depicted from the δ18O–elevation relationships obtained for each study area) over a most probable recharge area for each analyzed spring or well and, second, the calculation of the overlapping distribution between the spring/well mean δ18O values ± σ and the precipitation δ18O content for each outcropping aquifer. A new regional δ18O gradient covering 150 km latitudinal length of central Italy has been defined. Seven LMWL and δ18O–elevation relationships able to represent the local precipitation isotopic composition have been obtained. The mean elevation of the springs and wells recharge areas have been assessed by a comparison between the obtained gradient with nine δ18O gradients available in the literature and those obtained at a local scale. The new isotopic modeling approach can stress whether the mere isotope modeling based on the stable isotope of oxygen agrees with the hydrogeological setting of the study areas. [ABSTRACT FROM AUTHOR]

Forecasting of water availability has become of increasing interest in recent decades, especially due to growing human pressure and climate change, affecting groundwater resources towards a perceivable depletion. Numerous research papers developed at various spatial scales successfully investigated daily or seasonal groundwater level prediction starting from measured meteorological data (i.e., precipitation and temperature) and observed groundwater levels, by exploiting data-driven approaches. Barely a few research combine the meteorological variables and groundwater level data with unsaturated zone monitored variables (i.e., soil water content, soil temperature, and bulk electric conductivity), and—in most of these—the vadose zone is monitored only at a single depth. Our approach exploits a high spatial-temporal resolution hydrogeological monitoring system developed in the Conero Mt. Regional Park (central Italy) to predict groundwater level trends of a shallow aquifer exploited for drinking purposes. The field equipment consists of a thermo-pluviometric station, three volumetric water content, electric conductivity, and soil temperature probes in the vadose zone at 0.6 m, 0.9 m, and 1.7 m, respectively, and a piezometer instrumented with a permanent water-level probe. The monitored period started in January 2022, and the variables were recorded every fifteen minutes for more than one hydrologic year, except the groundwater level which was recorded on a daily scale. The developed model consists of three "virtual boxes" (i.e., atmosphere, unsaturated zone, and saturated zone) for which the hydrological variables characterizing each box were integrated into a time series forecasting model based on Prophet developed in the Python environment. Each measured parameter was tested for its influence on groundwater level prediction. The model was fine-tuned to an acceptable prediction (roughly 20% ahead of the monitored period). The quantitative analysis reveals that optimal results are achieved by expoiting the hydrological variables collected in the vadose zone at a depth of 1.7 m below ground level, with a Mean Absolute Error (MAE) of 0.189, a Mean Absolute Percentage Error (MAPE) of 0.062, a Root Mean Square Error (RMSE) of 0.244, and a Correlation coefficient of 0.923. This study stresses the importance of calibrating groundwater level prediction methods by exploring the hydrologic variables of the vadose zone in conjunction with those of the saturated zone and meteorological data, thus emphasizing the role of hydrologic time series forecasting as a challenging but vital aspect of optimizing groundwater management. [ABSTRACT FROM AUTHOR]

Nowadays, groundwater is the most important resource on our planet. However, due to population growth, urbanisation, and climate change, this resource is often overexploited or contaminated. In this context, carbonate aquifers provide drinking water to approximately 25% of the global population. Due to aquifers heterogeneities and anisotropic fracture systems, they can be affected by potential contamination and their optimal exploitation represents a challenge aspect. In this particular scenario, carbonate mountain aquifers encompass valuable groundwater resources due to their high recharge rates and excellent water quality; therefore, the understanding of their hydrogeological characteristics are vital for aquifers protection and water management. A valid solution to explore water movement within such aquifers and to quantify the groundwater amount can be offered using artificial tracers. At the same time, the geomechanical surveys can deep the knowledge on fracture density and orientation, providing valuable insights about fracture connection and conductivity. This study combines the advantages of six artificial tracer tests performed in four deep wells (260-500 m b.g.l.) and a geomechanical survey used, among other, to estimate hydraulic conductivity of a mountainous carbonate aquifer located in Central Italy. The results obtained by different methods highlighted the presence of multiple layers with higher conductivity values, able to sustain the groundwater flow without significant piezometric level drawdown during water pumping operations. This approach provides an effective support to the water management company operating. [ABSTRACT FROM AUTHOR]

The study aims to demonstrate that an effective solution can be implemented for modeling complex carbonate basins, in the situation of limited data availability. Considering the alternative modeling approaches under circumstances of data shortage is more significant knowing the vulnerability and effectiveness of these kinds of basins to drought and climate change conditions. In this regard, a hybrid approach that combines time series analysis and reservoir modeling is proposed to describe behavior in carbonate basins. Time series analysis estimates the contributing area and response time of the fractured carbonate system beyond the catchment's hydrographic boundaries. The results obtained align with previous literature-based field surveys. This information is then used to develop a conceptual reservoir system using the GEOframe modeling system. The model is validated using in situ discharge observations and Earth observations (EO) data on evapotranspiration and snow. Model reliability is assessed using traditional goodness of fit indicators, hydrological signatures, and a novel statistical method based on empirical conditional probability. This approach enables detailed analysis and investigation of water budget components in Mediterranean carbonate catchments, highlighting their response to significant precipitation deficits. Overall, our results demonstrate that flows from carbonate rock areas outside the hydrographic boundaries significantly impact the water budget of the upper Nera River. The storage capacity of the carbonate basin plays a crucial role in sustaining river discharge during drought years. In a single dry year, meteorological drought is considerably attenuated, while in subsequent dry years, it is slightly intensified. Multi-year droughts result in slower recovery due to the time required for precipitation to replenish the depleted storage that supported river discharge in previous dry years. This unique behavior makes these basins particularly vulnerable to the more severe and frequent drought episodes expected under future climate change. [ABSTRACT FROM AUTHOR]

Placed at the center of theMediterranean, 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 (hy- dro)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 im- prove 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 empiri- cal 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). [ABSTRACT FROM AUTHOR]

When applying hydrological models at basin scale, it is essential to take into account the contribution of groundwater and its behaviour, together with the hydrological state before and after storm events. The main objectives of the present study were the evaluation and discussion of factors contributing to the formation of river discharge, how and to what extent these factors affect the risk of flood and, finally, how they are related to the type, duration and intensity of rainfall events, especially associated with flash floods. This was achieved by applying HEC-HMS models to a small watershed in central Italy, characterised by high hydrogeological risk. The watershed is equipped for total rainfall, river discharge and groundwater level measurement. In addition, double ring infiltrometric tests were performed during different hydrological periods. The results highlighted a direct correlation between flood risk and the hydrological period; the insertion of groundwater data in the model allowed for a sensitivity analysis of the relationship between the level of risk and the hydrogeological settings and properties of the area. Moreover, the analysis of some “extreme” events occurring in the summer period highlighted river behaviour in very different hydrological states. [ABSTRACT FROM AUTHOR]

This study presents the characterization of the recharge zone and the water renewal mechanisms of the Gorgovivo spring, which feeds the aqueduct of the Ancona province and represents one of the most important water resources in central Italy. Measurements of chemical, isotopic and tritium contents were taken to get a detailed understanding of the hydrogeological setting and water circulation features. The isotopic investigation carried out in this study was performed thanks to the presence of different gauging stations for measuring rainfall heights and isotopic contents in precipitations, which allowed us to draw the altitude gradient that correlates the oxygen-18 content in groundwater with the isotopic height of infiltration. This value changed over time (from -0.23‰ to -0.2‰/100 m) indicating the intake altitude for the Gorgovivo spring at a height ranging from 1030 to about 1200 m a.s.l. Tritium contents (about 8-13 TU for shallow springs present in the area, 6-8 TU for the Gorgovivo spring) and the different isotopic compositions confirm the supposed presence of a double pathway in the groundwater: the first one being shallow and very ast - the small springs in the area studied belong to this pathway - while the second is slower and deeper, reaching the bottom part of the basal aquifer. The groundwater recharging the Gorgovivo spring is therefore a combination of these two pathways. Isotopic composition and tritium contents have also allowed the recharge area and recharge mechanisms of this spring to be investigated, by comparing the results with surface water and shallow spring waters. As a result, the present study introduces the likelihood of the recharge area of the Gorgovivo spring extending to more distant places in the Umbria-Marche ridge, thus confirming the suitability of isotopic techniques as a remarkable tool for recharge area evaluation. [ABSTRACT FROM AUTHOR]