A physical/statistical data-fusion for the dynamical downscaling of GRACE data at daily and 1 km resolution

GRACE (Gravity Recovery And Climate Experiment) is one of the most important satellite instrument for terrestrial hydrology and water cycle analysis. It is the unique source of information for the Total Water Storage Change (TWSC) that includes the mostly unknown groundwater storage change. Its use for many socio-economic applications is however drastically reduced by its spatial (≃200 km) and temporal (≃ monthly) resolutions. A statistical/physical dynamical downscaling is proposed here to obtain High Resolution (HR) 1 km and daily TWSC estimates, using auxiliary information from other satellite and modeling data (i.e. precipitation, evaporation and river network direction from topography). This scheme utilizes the Water Budget (WB) closure, an hydrological model and a set of statistical tools. The quality of the results is demonstrated over the Po river basin, a very challenging basin for GRACE observations due to its relatively small size and complex contrasting surface types. It is shown that terrestrial runoff and river discharge are well disentangled in the obtained HR TWSC fields. The new TWSC data can also show the impact of weather events such as strong precipitations. This study demonstrates how the optimal combination of multiple Earth data can help us better describe the terrestrial water cycle at higher space/time resolutions.