Petrone, Paola (2025) Climate change effects on the groundwater recharge and groundwater availability of a karst aquifer in southern Italy. The case study of Avella Mts. strategic karst aquifer (Campania). [Tesi di dottorato]

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Abstract

Karst aquifers are among the most important groundwater reservoirs in many regions of the world, as they provide drinking water and support industrial and agricultural activities. These aquifers are essential for socio-economic development, groundwater-dependent ecosystems and environmental sustainability. Unfortunately, these aquifers are increasingly vulnerable to threats from unsustainable exploitation, pollution and the effects of climate change with negative impacts on both the quantity and quality of groundwater resources. This Ph.D. thesis focused on the complex challenge of estimating the recharge and availability of groundwater resources of Avella Mts. karst aquifer, with particular attention to the impacts of climatic change. The Avella Mts. system was selected as a sample aquifer for its strategic hydrogeological importance at the regional scale. For the study area, characterised by significant climatic variability, geomorphological and stratigraphic complexity, due to the presence of discontinuous ash-fall pyroclastic soil cover and a lack of systematic data at high altitudes, this research highlighted the importance of estimating groundwater recharge and identifying the factors that affect this process, considering the strategic relevance of this aquifer for current and future water supply. For this research, an integrated multi-method, multi-temporal and multi-scale approach was applied, which represents a valuable tool for developing strategies to ensure sustainable use of groundwater resources in both the short and long term. An important first step in this study was the revision of the hydrogeological conceptual model of the Avella Mts. This updated model defines the lithology of the aquifer, its deep geometry and, for the first time, the groundwater flow scheme, identifying a compartmentalised aquifer system consisting of five distinct basins. At the aquifer scale, recharge was estimated using the Turc formula and MODIS satellite data ranged from 7.30 to 6.90 m³/s, with strong agreement between methods, confirming their validity. A comprehensive multi-scale water balance was performed using the Soil Water Balance (SWB) model. The results show a high spatio-temporal variability of recharge and a budget imbalance within the aquifer and its groundwater basins, which is particularly pronounced during drought years, as evidenced by the drying up of springs and streams. This research used Regional Climate Models (RCMs) projections to assess the impact of climate change on groundwater recharge under the IPCC Representative Concentration Pathways (RCP4.5 and RCP8.5). The projections indicated reductions in recharge in the short, medium and long term compared to the historical reference period of up to 50% by 2100 for the most catastrophic scenario RCP8.5. The study was also extended to the piedmont sector of the Avella Mts., corresponding to the Baiano district. This area is of great hydrogeological interest because it hosts a piedmont karst aquifer that has been used for a long time to supply groundwater to local communities. At the sectoral scale were estimated: i) groundwater recharge through the hydrological balance; ii) aquifer productivity through pumping tests; iii) groundwater hydrochemical quality. The results show significant groundwater resources, high groundwater quality and yield for this sector of the aquifer. At the site-specif scale, field surveys and laboratory analyses improved our knowledge of the hydrogeological role of the ash-fall pyroclastic soil cover on the recharge processes of the karst aquifer. This knowledge is constantly increasing through the design and implementation of an experimental observatory equipped in the Foce hydrogeological basin, where all the parameters of the hydrogeological balance are measured continuously and in real-time by an integrated monitoring system. The installed instruments allow the continuous monitoring of the following hydrological variables: i) precipitation and air temperature, by means of weather stations located inside and outside the forest; ii) soil water content to a depth of 1.20 m, by means of multilevel probes; iii) matric potential by means of water potential sensors; iv) water infiltration by means of a natural multilevel lysimeter with data logger; v) total runoff, by means of a Venturi channel and a radar sensor with data logger; vi) piezometric levels and spring discharges, by means of level and velocity sensors with data logger. Data from this monitoring, combined with detailed stratigraphic characterisation and hydraulic parameter determination, were used to implement and calibrate the HYDRUS-1D numerical model for a 3-year simulation period of hydrogeological variables (e.g. infiltration and evapotranspiration). The simulation results emphasized seasonal dynamics of the hydrogeological variables in the unsaturated zone and the role of canopy interception in modifying effective precipitation. The results obtained are considered particularly significant as they represent an improvement of the hydrogeological knowledge that, for most aquifers of the southern Apennines, seems to be only general and not suitable for the application of advanced models aimed at estimating the effects of climate change scenarios. Finally, the proposed approach is designed to be exportable to other karst aquifers of southern Italy and the world, with similar characteristics.

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