Interannual variability in water storage over 2003 - 2007 in the Amazon Basin 2 from GRACE space gravimetry , in situ river level 3 and precipitation data

27 We investigate the interannual variability over 2003-2007 of different hydrological parameters in 28 the Amazon river basin: vertically-integrated water storage from the GRACE space gravimetry 29 mission, surface water level over the Amazon River and its tributaries from in situ gauges, and 30 precipitation. We analyze the spatio-temporal evolution of total water storage from GRACE and 31 in situ river level along the Amazon River and its main tributaries. We also perform an Empirical 32 Orthogonal Decomposition of the total water storage, river level and precipitation over the whole 33 basin. We find that this period is characterized by two major hydrological events: a temporary 34 drought that affected the western part of the basin during year 2005 and very wet conditions in 35 the eastern, northern and southern regions of the basin, peaking in mid-2006. Derivative of basin-36 average water storage from GRACE is shown to be highly correlated to the Southern Oscillation 37 Index, indicating that the spatio-temporal change in hydrology of the Amazon basin is at least 38 partly driven by the ENSO (El Nino-Southern Oscillation) phenomenon, as noticed in previous 39 studies. 40 41