title: Enhanced groundwater recharge rates and altered recharge sensitivity to climate variability through subsurface heterogeneity.
abstract: Our environment is heterogeneous. In hydrological sciences, the heterogeneity of subsurface properties, such as hydraulic conductivities or porosities, exerts an important control on water balance. This notably includes groundwater recharge, which is an important variable for efficient and sustainable groundwater resources management. Current large-scale hydrological models do not adequately consider this subsurface heterogeneity. Here we show that regions with strong subsurface heterogeneity have enhanced present and future recharge rates due to a different sensitivity of recharge to climate variability compared with regions with homogeneous subsurface properties. Our study domain comprises the carbonate rock regions of Europe, Northern Africa, and the Middle East, which cover ∼25% of the total land area. We compare the simulations of two large-scale hydrological models, one of them accounting for subsurface heterogeneity. Carbonate rock regions strongly exhibit "karstification," which is known to produce particularly strong subsurface heterogeneity. Aquifers from these regions contribute up to half of the drinking water supply for some European countries. Our results suggest that water management for these regions cannot rely on most of the presently available projections of groundwater recharge because spatially variable storages and spatial concentration of recharge result in actual recharge rates that are up to four times larger for present conditions and changes up to five times larger for potential future conditions than previously estimated. These differences in recharge rates for strongly heterogeneous regions suggest a need for groundwater management strategies that are adapted to the fast transit of water from the surface to the aquifers.
authors.affiliation: Institute of Earth and Environmental Sciences, University of Freiburg, 79098 Freiburg, Germany; andreas.hartmann@hydrology.uni-freiburg.de.|Department of Civil Engineering, University of Bristol, BS8 1TR Bristol, United Kingdom.
authors.forename: Andreas
authors.initials: A
authors.lastname: Hartmann
authors.affiliation: Department of Civil Engineering, University of Victoria, Victoria, BC V8W 2Y2, Canada.|School of Earth and Ocean Sciences, University of Victoria, Victoria, BC V8W 2Y2, Canada.
authors.forename: Tom
authors.initials: T
authors.lastname: Gleeson
authors.affiliation: International Institute for Applied Systems Analysis, A-2361 Laxenburg, Austria.|NASA Goddard Institute for Space Studies, New York, NY 10025.|Center for Climate Systems Research, Columbia University, New York, NY 10025.|Department of Physical Geography, Utrecht University, 3584 CS Utrecht, The Netherlands.
authors.forename: Yoshihide
authors.identifier: 0000-0003-4770-2539
authors.initials: Y
authors.lastname: Wada
authors.affiliation: Department of Civil Engineering, University of Bristol, BS8 1TR Bristol, United Kingdom.|Cabot Institute, University of Bristol, BS8 1TR Bristol, United Kingdom.
authors.forename: Thorsten
authors.initials: T
authors.lastname: Wagener
keywords: climate change; climate variability; groundwater recharge; subsurface heterogeneity; water resources