Recharge of aquifers can only occur where excess water is able to penetrate beyond the reach of plant roots and shallow sub-surface flow. The rate and generic behavior of recharge lie at the interface of understanding between hillslope, vadose zone, groundwater, and eco hydrology. 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. Furthermore, human activity leads to several additional sources of groundwater recharge such as irrigation, leaking urban water infrastructure etc. Solute and particle matter inflow to the groundwater are coupled to these different kinds of processes whereas their sources are natural or from agricultural or industrial land use.

Catchment hydrologists may view 'subsurface runoff' as a simple loss term, while groundwater modelers may approximate 'recharge' merely as a fraction of rainfall. Both groups try to quantify the complicated, non-linear process of that part of the rainfall that makes it through the vadose zone to the groundwater table. The study of recharge is inherently a multi-disciplinary field where experts in catchment hydrology, vadose zone hydrology, and groundwater hydrology 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 modeling approaches with respect to quantify water and solute transport through the unsaturated zone to the groundwater.