GRACE mass concentration blocks (mascons) and hydrological modeling combined to determine temporal mass fluxes in large river basins of Southern Africa

GRACE mascons represent surface mass distribution as spatial and temporal step functions, and can be estimated on regional scales. We have designed a system of mascon blocks, with a spatial and temporal resolution of 1.5 x 1.5 deg and 10 days respectively. Initially the mascon normal equations were solved with uniform constraints applied between mascon parameters in space and time. This solution however, resembles previous mascon solutions with a lower spatial resolution, and shows a similar level of detail in the temporal distribution of terrestrial water masses. We believe that a higher level of detail in temporal water distribution can be retrieved from the GRACE data, by using the physics of hydrological models as a set of hydrological constraints to replace the traditionally used (non-physical) constraints. For this purpose, hydrological models of major river basins in Southern Africa built using SWAT (Soil and Water Assessment Tool) will be used. A sufficiently good model will be able to constrain the mascon parameters well enough for the estimated mass fluxes to contain a higher level of detail, compared to the non-physically constraint mascon parameters. This study is a part of the HYDROGRAV project (hydrograv.spacecenter.dk) which explores the utility of timelapse gravity surveys for hydrological model calibration and terrestrial water storage monitoring.