Tracking Spatiotemporal Variations in Groundwater Storage in the Lower Mississippi Region with GRACE Satellite data

The Lower Mississippi Region (LMR) is a fluvial-deltaic environment covering over ~280,000 km2 across the U.S Gulf Coast, consisting of the Coastal Lowlands and Mississippi River Valley Alluvium (MRVA) aquifer systems. Porous clay-rich sediments within the aquifers provide pathways for large volumes of groundwater infiltration, with over 7.5 billion m3 pumped daily for agricultural and irrigation purposes. Approximately 80% of the LMR population relies on groundwater for freshwater supplies; however, continuous development causes the depletion of groundwater resources, thus posing environmental hazards including irreversible land subsidence, extensive inundation during flooding, and anthropogenic sea-level rise. Our objective is to provide a quantitative analysis of the groundwater conditions throughout the LMR using satellite gravity data and land assimilation models to provide new insights into groundwater usage and forecast future trends to improve water management further. We have compiled 18 years of data from NASAs Gravity Recovery and Climate Experiment (GRACE) published as near-monthly spherical harmonic coefficients that show gravitational anomalies without the effect of atmospheric pressure, ocean-bottom pressure, and Earth tides, therefore, permitting interpretations of mass variations related to changes in equivalent water height (EWH). Recent research shows that the resolution of GRACE data can be optimized for catchments at scales of ~55 km x 55 km by using statistical downscaling algorithms and parametrizing the data using hydrological models that include components such as precipitation, evapotranspiration, and runoff. Our preliminary results that correspond to the period between 2002-2013 are indicative that post-processed GRACE data can distinguish EWH variations at centimeter-scales for watersheds in the LMR, comparable to previous work. Monthly amplitudes of EWH for the LMR range from approximately 30 cm over the 18-year period, with identifiable differences in watersheds east of the Mississippi River compared to western watersheds. These observable differences may potentially reflect consequences of exhaustive groundwater extraction in the Coastal Lowlands in comparison to the MRVA aquifer system.