A multiscale soil water balance for sustainable groundwater management of a local transboundary karst aquifer

Sustainable groundwater management of transboundary aquifers (TBAs) remains a major global and regional challenge that requires necessitating enhanced, coordination and cooperation among neighboring countries and institutions. The Avella Mts. are a major karst TBA of the Campania region (Italy), providing vital groundwater resources, whose water balance equilibrium is increasingly threatened by uncontrolled growth in groundwater extraction, especially during prolonged drought periods. A multiscale soil water balance was performed for the period 2010–2021 to assess the sustainability of current groundwater withdrawals. The findings reveal a high spatio-temporal variability of groundwater recharge (GR). At the aquifer scale, average GR equals to 244.40 Mm3/y, with interannual variability of about - 45 % and +73 %. At the basin scale, recharge on average varies between 29.64 Mm3/y and 100.28 Mm3/y. The springs inventory map and the register of authorized wells highlight an outgoing groundwater volume of 252.30 Mm3/y, at the aquifer scale, while at the basin scale, it varies between 6.30 Mm3/y and 97.76 Mm3/y, exceeding the recharge in certain groundwater basins. Consequently, there is a budgetary disequilibrium within the aquifer, which is particularly pronounced during drought years, as evidenced by the drying of springs and streams. These results highlight significant aquifer stress, which is projected to worsen in the future due to climate change. They demonstrate the urgent need to adopt sustainable groundwater management strategies and reform existing water governance model in the Campania region, as well as in other parts of Italy and Europe.