Estimating the distribution of contemporary (<50 year old) groundwater on Earth

Wednesday, 17 December 2014: 2:50 PM
Kevin M Befus1, Thomas P Gleeson2, Elco Luijendijk3, Scott Jasechko4 and M. Bayani Cardenas1, (1)University of Texas at Austin, Austin, TX, United States, (2)McGill University, Montreal, QC, Canada, (3)Georg-August-Universitaet Goettingen, Goettingen, Germany, (4)University of New Mexico Main Campus, Albuquerque, NM, United States
Time-scales of groundwater dynamics can control how groundwater interacts with many Earth system processes, including weathering, the transport of solutes or contaminants, and hydrologic responses to climate change. In this study, we quantified the global volume and distribution of groundwater that has been recharged over the past 50 years, a time-scale relevant to current policy planning and intimately tied to human generations. We modelled groundwater residence time distributions with several thousand two-dimensional flow and age-as-mass transport simulations guided by global datasets of basin geometric and hydraulic properties. The models suggest that less than 15% of the groundwater on Earth to 2 km depth was recharged in the past 50 years. For most watersheds on Earth, this young groundwater is restricted to the upper 100 m of the Earth’s crust. Uncertainty in our estimate stems from the simplification of two-dimensional flow and uncertainty in permeability and porosity.