This project will contribute to the overarching goals of the RU by (1) providing optimized alternative GRACE data sets including specific uncertainty information and by (2) leading the validation efforts to assess the C/DA results against independent data. Regarding the first objective, the potential of non-standard GRACE solutions for C/DA will be investigated, at the beginning focusing on alternative spatial representations (e.g. mascon solutions) and successively also taking temporally higher-resolution (daily) time series into account. Furthermore, this project will develop a consistent treatment of localized water mass signals (e.g. reservoirs, rivers) that are below the spatial resolution of GRACE but large in magnitude and can therefore have a significant impact on the C/DA results. In the second objective, the output of various variants of model runs (with and without C/DA, before and after implementing new model structures) will be validated against compartmental water storage changes (e.g. soil moisture, groundwater levels) derived from independent observations and high-resolution regional models.