Continental water storage inferred from 3-D GPS coordinates in Danube Basin

GPS coordinates time series contain viable information about continental water storage (CWS) at global and regional scale. The permanent GPS network of GPS stations around the Earth recorded more than 15 years of data, which comprise the elastic response of the bed rock movements induced by mass loading. The inversion of the observed displacements, yields mass variations which can be interpreted as CWS under the condition that no other mass loading is interfering. GPS-derived CWS offers complimentary information to the widely used CWS determination by GRACE but is also able to mitigate a possible loss of data in case the GRACE mission ends before the launch of the GRACE Follow-On mission. GPS also allows increasing the temporal resolution (weekly from GPS versus monthly from GRACE) and the spatial resolution (especially in the regions with dense GPS networks). Here, we determine the weekly mass variations from GPS 3-D coordinates by using mass-loading Green's function in six Danube sub-basins. The results are validated against GRACE and hydro-meteorological models. We also demonstrate the contribution of GPS horizontals for regional water storage and provide insights into the benefits and limitations of 3-D GPS inversions for regional water storage.