Gridded time series of total water storage anomalies (TWSA) as simulated by a number of WaterGAP model variants that were subjected to different C/DA variants are being used by P9 for simulating surface displacements. These displacements are then compared to geodetic observations (GNSS 3-dimensional surface displacements) in the training and critical regions as well as in the validation regions. In addition, TWSA simulated by WaterGAP without C/DA will be validated globally. The resulting measure of fit between observed and simulated displacements are interpreted with respect to the performance of C/DA. In the regional analyses where there is sufficient GNSS data, we will use the observations to invert for the water storage itself. A goal of this project will be to precisely quantify the errors in the GNSS observations and the background models used to forward model the displacements.