Integrating GRACE Satellite and Ground-based Estimates of Groundwater Storage Changes

Groundwater storage depletion is a critical issue for many of the major aquifers in the U.S., particularly during intense droughts. The GRACE (Gravity Recovery and Climate Experiment) satellites launched in 2002, with sensors designed to measure changes in the Earth’s gravitational field at large spatial scales (≥ ~200,000 km2). These changes are primarily driven by changes in water storage on the Earth’s surface. Estimates of groundwater storage changes based on these gravity measurements have attracted considerable media attention in the U.S. and globally. However, groundwater storage changes are computed indirectly by subtracting snow, surface water, and soil moisture storage from the total water storage monitored by GRACE, and therefore these estimates can reflect accumulated errors in the other component estimates. With increasing applications of GRACE satellite data, some suggest that we could greatly reduce ground-based monitoring and modeling of groundwater storage changes, but the large uncertainties associated with these data sets remain an obstacle to the broader utilization of GRACE data. Recent studies suggest potential for addressing the uncertainties in GRACE-based estimates through the application of a range of techniques to a given region. The purpose of this project is to combine ground-based and model-based groundwater storage estimates with GRACE data to construct a national map of groundwater depletion. Long-term trends and spatial and temporal variability in groundwater storage changes will be examined and uncertainties in each approach will be evaluated. The integrated dataset will be used to assess natural versus anthropogenic variations in groundwater storage in response to droughts and floods. This analysis should significantly enhance our understanding of groundwater storage changes and inform groundwater management decision making.

Figure: Groundwater basins outlined against a background of an example GRACE grid from October 2002. To the right are the trends in monthly water storage anomalies for these four aquifers from 2002-2015 (relative to a 2004-2010 baseline average).



Publications:



Rateb, A., Scanlon, B. R., Pool, D. R., Sun, A., Zhang, Z., Chen, J., et al. (2020). Comparison of groundwater storage changes from GRACE satellites with monitoring and modeling of major U.S. aquifers. Water Resources Research, 56, e2020WR027556.

https://doi.org/10.1029/2020WR027556



Principal Investigator(s):

Bridget Scanlon (UT at Austin)

Ward E Sanford (Branch of Regional Research, Eastern Region)

Matthew Rodell (National Aeronautics and Space Administration)

Meredith D Reitz (Branch of Regional Research, Eastern Region)