The global distribution of modern groundwater derived from high-resolution 3-D flow path simulations

Abstract

Research on groundwater and its sustainable management has become increasingly significant due to growing water requirements and over-abstraction of groundwater resources. The time that water spends in the subsurface is an essential feature for the understanding of the dynamics of groundwater systems and patterns. Modern groundwater, which only represents the water in the subsurface recharged after above-ground thermonuclear testing fifty years ago, is of major interest as it is most vulnerable to global change, but also able to indicate renewable aquifers. The primary aim of this study was to improve recent estimates of the global volume and the distribution of modern groundwater using high-resolution 3-D flow path simulations. In order to analyse the results, they were compared to the research by Gleeson et al. (2015). The total groundwater volume in the continental crust is estimated at 4.2 million km3, of which approximately 147 thousand km3 or 3.5% is younger than fifty years. The volume of modern groundwater is equal to a depth of 1.1 m if it was extracted and pooled at the earth’s land surface like a flood; almost 3 times smaller than presented by Gleeson et al. (2015). The model’s spatial distribution of modern groundwater is mainly controlled by mountainous and coastal areas while river systems are underrepresented. The relatively modest groundwater volumes are assumed to be largely dependent on the aquifer thickness and the resolution of input data.