Combining space gravimetry and other satellite observations to reduce spatial uncertainties

GRACE and GRACE-FO missions have provided gravity fields water mass changes within the Earth's surface since 2002.  This gravity fields are post-processed to infer water mass changes between Ocean and land storage compartments. Unfortunately, most storage compartments (lakes, groundwater, glaciers…) are too small to be resolved given the current spatial resolution of gravimetry missions, resulting in Leakage and Gibbs effects.This effects generates spurious signals that makes gravimetry-based Land water storage (LWS) changes estimates difficult to attribute and to interpret at individual basin and regional scales.
Here, we combine gravimetry-based water mass change data with independent satellite observations to derive refined estimates of the water mass changes. The combination consists in including observations from  satellite altimetry and high resolution visible imagery of glacier (Hugonnet et al., 2021) and lake (Cretaux et al., 2016) mass changes in the conversion process from gravity L2 data to water mass changes. The combination is done for all regions of the world on a monthly basis.
This approach allows to reduce the uncertainty in LWS changes at interannual to decadal time scales, and to derive glacier-free estimates of TWS in the endorheic basins and the exorheic basins.
We find that for the period from 2002 to 2021, the total LWS trend of 0.30±0.26 mm SLE/yr is mainly due to a mass loss in endorheic basins LWS of 0.24±0.13 mm SLE/yr. Over the same period, exorheic basins control interannual variability (2-5 years) but present a non-significative trend of 0.06±0.14 mm SLE/yr.