Talk Title:  Advances in Global Hydrology based on GRACE Satellite Gravimetry

Abstract:  Two decades of GRACE (Gravity Recovery and Climate Experiment) satellite data have significantly advanced our understanding of global hydrology. GRACE satellites measure variations in Earth’s gravity which are controlled mostly by water storage changes, such as those related to droughts, floods, ice melting, and human water use. The vertically integrated land total water storage (TWS) variations monitored by GRACE 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 parameter in assessing climate impacts in hydrology and increasing use of TWS in global models. GRACE is like a scale in the sky, providing the big picture, and ideal for monitoring freshwater contributions to sea level rise. 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. 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.

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