Recharge of aquifers occurs where excess water is able to penetrate beyond the reach of plant roots and shallow sub-surface flow. The rate of recharge lies at the interface of understanding between hillslope, vadose zone, groundwater, and ecohydrology. Hillslope and karstic recharge may be driven by water infiltrating during major storm events, particularly in semi-arid areas. In colder regions, snow melt may be the dominant factor. In heavily humanly modified surface areas, human activity leads to several additional sources of groundwater recharge as irrigation and leaking urban water infrastructure. A climate warming can contribute to reduce the groundwater recharge. On the other hand, both an excess of recharge with the consequent water table rise, and a climate warming can lead to an increase of evaporation from the water table and finally to soil salinization, with crucial fallout on the soil quality. Solute and particle matter inflow to the groundwater are coupled to these processes whereas their sources are natural or from agricultural or industrial land use.

Located at the interface between vadose zone and groundwater, and due to its temporal and spatial variability, the estimate of groundwater recharge is still a major challenge to assess the water balance both of the soil and of the groundwater. Both catchment hydrologists, soil hydrologists and groundwater modellers try to quantify the complicated, non-linear process of aquifer's recharge which remains inherently a multi-disciplinary field where experts with different background need to work together. The purpose of this session is to bring these different groups together and to discuss recent advances in the spatial and temporal monitoring and modelling approaches with respect to quantify water and solute transport through the unsaturated zone to the groundwater.