Investigating the Application of GRACE Derived Groundwater Storage Change in a Confined Aquifer System through a Water Balance Comparison

Abstract:

Regional scale hydrologic research is limited by scarce in-situ measurements and the challenges of representing the heterogeneity of basin characteristics and water fluxes between sampled locations. Since 2002, GRACE and GRACE-FO derived measures of change in total water storage (TWS) have provided researchers insight into water cycle trends at large scales but additional information is required to partition the hydrologic cycle into its component fluxes. Groundwater changes are an important component of this signal. While attribution of the GRACE signal to TWS changes in unconfined aquifers has been well studied, GRACE derived measurements of TWS changes in confined aquifers is still poorly understood. The Guarani Aquifer System (GAS) and the overlying Parana River Basin are well suited to a case study of TWS change detection in confined aquifers, specifically accounting for fluxes attributable to groundwater storage changes. The GAS is a 1.1 million km², nearly fully confined aquifer with regional importance as a water supply source. In this study, we compare TWS change from GRACE to changes from a surface water budget to identify areas where fluxes within and from the underlying groundwater system may be identifiable. The surface water budget is calculated using remotely sensed precipitation and evapotranspiration and observed streamflow. The long-term goal of this research is to determine whether differences in the GRACE derived TWS changes compared to the surface water budget can be attributed to changes in TWS within a confined aquifer system.