Effects of ash-fall pyroclastic soil mantle on groundwater recharge of Terminio Mt. peri-volcanic karst aquifer

Terminio Mt. karst aquifer, Campania region, southern Italy Karst aquifers are largely exploited, but the assessment of groundwater recharge in these aquifers is still considered challenging due to: i) the disregarding of the hydrological role of the soil coverings; ii) the lack of a spatially homogeneous coverage of rain and air temperature monitoring stations. Here we propose a multi-methodological approach to evaluate the groundwater recharge of the Terminio Mt. karst aquifer. This aquifer is mantled by ash-fall pyroclastic soils fostering the development of a luxuriant vegetation. A field and laboratory characterization of soil coverings was performed, and the spatial and temporal variability of groundwater recharge was estimated by the Soil Water Balance code. A variability of thickness of ash-fall pyroclastic soils, ranging between 0.40 m and 1.00 m, classified as sandy loam, were found. These features resulted in variable groundwater recharge and evapotranspiration rates depending on land cover classes and thickness of pyroclastic soils. Outcomes show the relevant hydrological role of soil coverings whose relevant water retention, up to 427.8 mm, coupled with the significant precipitation, exceeding 1,000 mm·yr-1 in average, results in a value of the actual evapotranspiration equal to the potential one. The approach proposed advances the understanding of the infiltration-evapotranspiration trade-off which regulates the spatial and temporal variability of groundwater recharge.