Groundwater resources are critical for the freshwater supply of humanity, for drinking water purpose and agricultural irrigation. At the same time, many aquatic and terrestrial ecosystems are directly or indirectly dependent of groundwater. Climate change, population increase and the resulting changes in land use and water demand exert increasing pressure on these valuable but vulnerable groundwater resources, often resulting in declining water tables and spring discharge, saltwater intrusions in coastal aquifers, reduced environmental baseflow and, consequently, deterioration of ecosystems and water-use conflicts. This session addresses all aspects of groundwater availability, both at global scales and in relevant regional case studies, in different types of aquifers – unconsolidated aquifers, fractured rocks and karst aquifer systems, with a particular focus on the Alpine and Mediterranean regions. Contributions presenting new experimental, conceptual and modelling methods and tools to address different aspects of groundwater availability across all scales are also welcome.