The Global Gravity-based Groundwater Product (G3P)

Due to the fundamental role of Groundwater (GW) in the Earth's water and energy cycles, GW has been declared as an Essential Climate Variable (ECV) by GCOS, the Global Climate Observing System. However, within Copernicus - the European Earth Observation Programme - there is no service available yet to deliver data on this fundamental resource, nor is there any other data source worldwide that operationally provides information on changing groundwater resources in a consistent way, observation-based, and with global coverage. Hence, the Global Gravity-based Groundwater Product (G3P) aims at developing a satellite-based groundwater storage (GW) data set as a new product for the EU Copernicus Climate Change Service. G3P capitalizes from the unique capability of GRACE and GRACE-FO satellite gravimetry as the only remote sensing technology to monitor subsurface mass variations, and from other satellite-based water storage products to provide a data set of groundwater storage change for large areas with global coverage. G3P is obtained by using a mass balance approach, i.e., by subtracting satellite-based water storage compartments (WSCs) such as snow water equivalent, root-zone soil moisture, glacier mass, and surface water storage from GRACE/GRACE-FO monthly terrestrial water storage anomalies (TWSA). For a consistent subtraction of all individual WSCs from GRACE-TWSA, the individual WSCs are filtered in a similar way as GRACE-TWSA, where optimal filter types were derived by analyses of spatial correlation patterns. G3P groundwater variations are provided for almost two decades (from 04-2002 to 12-2020), with monthly resolution, and at a 0.5-degree spatial resolution globally. In this contribution, we also illustrate some results of the G3P data set and of its uncertainties, as well as its evaluation by independent in-situ groundwater observation.

 

This study has received funding from the European Union’s Horizon 2020 research and innovation programme for G3P (Global Gravity-based Groundwater Product) under grant agreement nº 870353.