GRACE is a remote sensing of water storage based on gravity field. The two twin NASA's Gravity Recovery and Climate Experiment (GRACE) mission detect the gravitational field of the Earth surface. Since the effect of land mass (or large body) in the change of gravitational field is small, and slow, the main change is due to the change in water mass. The terrestrial water has a mass, and always in motion. So measuring the time varying gravitational field is measuring the total water storage of the earth. This gives the hydrologist unprecedented chance to see and understand how much they are able to close the water budget modelling. Since the total water storage (TWS) is the main sources of water for use, and it the aggregated values of the water fluxes, the GRACE data will help the water resource managers and policy planners to be very proactive.
Recently, I have been starting to explore this dataset if it is possible to use in basin hydrological modelling. While I will come back to the results of the study in the future, here is the GRACE map of Ethiopia for some years (2002-2008) at monthly time steps. I presented the map in animation below. It is estimated at zonal level. Note that the unit is cm.