Karst aquifers of the Southern Apennines represent hydrogeological systems of primary importance for water supply, baseflow regulation, and the conservation of groundwater-dependent ecosystems. These aquifers develop within thick Mesozoic carbonate series composed mainly of limestones and dolostones, intensely fractured and karstified and characterised by high structural and hydraulic heterogeneity. Due to the structural setting of the Southern Apennines Chain, these aquifers form the major mountain ranges and are characterised by autonomous groundwater circulation feeding huge basal springs. Understanding groundwater recharge processes is therefore essential for assessing groundwater availability and aquifer vulnerability under climatic and environmental change.
The effects of global climate change are superimposed on this natural variability. Regional climate projections indicate increasing air temperatures, decreasing precipitation, and greater rainfall irregularity throughout the twenty-first century. Under both analysed emission scenarios, effective precipitation shows negative trends, suggesting a significant reduction in the potential recharge of carbonate aquifers. These reductions are more pronounced under high-emission scenarios, implying increased frequency and duration of water-stress conditions.
Groundwater recharge in these aquifers is controlled by the interaction among geological structures, topography, soil cover, climatic conditions, land use, and the widespread presence of ash-fall pyroclastic soils mantling carbonate massifs. Infiltration occurs both as concentrated recharge along karst landforms and tectonic discontinuities and as diffuse recharge mediated by soils and pyroclastic covers. These volcanic deposits, derived mainly from the Campanian volcanic districts, play a major hydrogeological role because of their high porosity, variable hydraulic conductivity, and strong water-retention capacity. Acting as intermediate reservoirs, they store rainfall and gradually release water towards the underlying carbonate bedrock, thereby regulating infiltration and recharge dynamics. Depending on their thickness and stratigraphy, pyroclastic covers may either enhance groundwater recharge through delayed percolation or increase evapotranspiration losses. The assessment of groundwater recharge of these aquifers is a challenging task due to the lack of meteorological stations a the higher altitudes and temporal discontinuity of time series. However, by means of empirical approaches and considering RCM data this assessment has been progressively refined.
Long-term analyses of precipitation and air temperature time series reveal significant climatic variability at annual and decadal scales. Total and effective precipitation exhibit cyclical oscillations that directly influence aquifer recharge. These fluctuations are closely related to large-scale atmospheric circulation patterns, particularly the North Atlantic Oscillation (NAO), which strongly controls rainfall distribution across the Mediterranean and the Southern Apennines. Variations in effective precipitation, considered a proxy for groundwater recharge, produce alternating phases of water surplus and prolonged deficits, with direct impacts on spring discharge and baseflow regimes.
Overall, the carbonate aquifers of the Southern Apennines emerge as highly sensitive systems to climatic and environmental change. The interaction between carbonate bedrock, pyroclastic covers, land use, and climate variability controls recharge dynamics across multiple spatial and temporal scales. Integrated assessment of these processes through climatic analyses and hydrological modelling is essential for sustainable groundwater-resource management and climate-change adaptation in Mediterranean karst environments.
