Reconstruction of Groundwater Depletion Using a Global Scale Groundwater Model

Abstract:

Groundwater is a crucial part of the global water cycle. It is the world’s largest accessible source of fresh water to satisfy human water needs. During times of droughts it sustains river flows and evaporation in areas with shallow water tables. However, most global scale hydrological models do not include a lateral groundwater flow component due to a lack of consistent global-scale hydrogeological information. Such data is needed to arrive at a more realistic physical representation of the groundwater system allowing for the simulation of groundwater head dynamics and lateral flows including abstractions in confined and unconfined aquifers. This improved process description is indispensable to understand the effects of past and future climate variations and human dependence on global water resources. In this study we developed a high resolution (5 arc-minutes) global scale transient groundwater model presenting confined and unconfined aquifers. This model is based on MODFLOW (McDonald and Harbaugh, 1988) and coupled with the land-surface model PCR-GLOBWB (van Beek et al. 2011) via recharge and surface water levels. The aquifer parameterization is based on available global data-sets on lithology (Hartmann and Moosdorf 2011) and permeability (Gleeson et al. 2011) and newly derived estimates of aquifer depth and thickness of confining layers from an integration of lithological and topographical information. In a sensitivity analysis the model is run with various hydrogeological parameter settings, under natural recharge only. Scenarios of past groundwater abstractions and recharge (Wada et al 2012) are evaluated. Trends and fluctuations of groundwater head and streamflow are studied in response to human groundwater use and climate variability, as well as revealing hotspots and magnitude of global groundwater depletion.