Monitoring groundwater resource is today challenging because of very scarce in situ measurement networks. Here we combine 7 years (2003-2009) of data from the Gravity Recovery and Climate Experiment (GRACE) satellite mission with outputs of four Land Surface Models to detect Groundwater Storage (GWS, water stored below the 1-10 m upper layers) variations. The method is applied on two great aquifers with different climatic regime and anthropogenic forcing: the Guarani Aquifer System (South America) and the Canning Aquifer (Australia). For the former, we find groundwater depletion at a rate of 8 km 3 /year in the southern part. At the aquifer scale, this depletion is compensated by a GWS increase at a similar rate in the northern part. At this scale, despite increasing development in groundwater use, GWS variations during the studied time span may be considered as negligible compared to the hydrological variability. The negative trend seen by GRACE over the Guarani Aquifer can be mainly explained by change in water storage of the upper soil layers. On the contrary, in the Canning Basin, results show an important groundwater depletion (after accounting for the upper soil layer component) corresponding to a water volume loss of almost 80 km3 for the whole study period. Since groundwater pumping is little developed in this arid region, the depletion rather reflects climate-related variability in deep water storage due to a return to normal or even dry conditions in recent years after a particularly wet period, as confirmed by precipitation, evapotranspiration and Normalized Difference Vegetation Index (NDVI) data analysis.