Two decades of GRACE (Gravity Recovery and Climate Experiment) satellite data have significantly advanced our understanding of global hydrology. Variations in Earth’s gravity monitored by GRACE are controlled mostly by water storage changes, such as those related to droughts, floods, ice melting, and human water use. The vertically integrated GRACE land total water storage (TWS) variations include surface water, soil moisture, and groundwater. The value of the GRACE TWS parameter is evident in its recent adoption in the IPCC reports as an essential climate variable in assessing climate impacts in hydrology and increasing use of TWS in global models.

Attribution analysis of GRACE water storage variability to human and climate drivers has greatly advanced over time. GRACE satellites were the first to show large scale groundwater depletion in the IndoGangetic Basin. Interpretation of GRACE water storage has improved by integrating additional data on human intervention (e.g., groundwater pumping, water use, land use change) and climate drivers (e.g., precipitation, drought indices). Some basins show combined effects of human intervention amplifying or dampening climate effects. Recent studies show the value of ground-based monitoring and regional modeling to provide long-term context for GRACE data with large scale net increases in water storage in the IndoGangetic Basin and Northwest US over the past century.

Advances in GRACE processing shows potential value in operational mode for drought and flood warning. Continued advances in applications of GRACE data are expected by combining these data with other satellite data (e.g., SWOT, SMAP) and by using GRACE data to constrain models through data assimilation. The visual power of GRACE data helped communicate water storage variability to the public and influence water policy in many regions, including India and the US.

Bridget Scanlon is a Senior Research Scientist at the Bureau of Economic Geology, Jackson School of Geosciences, University of Texas at Austin. Her degrees are in Geology with a focus on hydrogeology. She has worked at the University of Texas since 1987. Her current research focuses on various aspects of water resources, including global assessments using satellites and modeling, management related to climate extremes, and water energy interdependence. She has authored ~ or co-authored ~170 publications. Dr. Scanlon is a Fellow of the American Geophysical Union and a member of the National Academy of Engineering.