tectonics and the mass transport in the Earth's system which induces deformation of the 43 Earth's crust in response to variations of the load due to hydrology, air pressure and non-44 tidal oceanic effects. Continuous GPS time series exceeding a decade are now available 45 which can provide reliable information on the long-term height evolution (linear and non-46 linear) as well as on the short-period seasonal fluctuations. However, it is complicated to 47 unravel the contribution of the different components in the observed long-term height 48 behavior because, at global scale, the Glacial Isostatic Adjustment (GIA) is the only 49 coherent geological contribution to height variation for which understanding of the 50 physical process has been achieved. Superconducting gravimeter and/or absolute gravity 51Page 3 of 60 A c c e p t e d M a n u s c r i p t 3 measurements are not as widely spread as those of GPS, but where both types of 52 measurements are available, they offer a unique means to detect and understand mass 53 contributions. 54It was shown that hydrological mass variations play a major role in the seasonal 55 height and gravity variability (van Dam et al., 2001; Zerbini et al., 2007). On long time 56 scales, climate-related variations of GPS heights and gravity have not yet been clearly 57 identified mainly because of the limited temporal extent of most of the continuous series 58 and for the lack of information on the spatial and temporal variability of groundwater 59 storage. 60We have studied the variations observed during the last decade in the GPS heights, 61 gravity and the hydrological time series in northeastern Italy (Fig. 1), as well as their 62 mutual relationships. The investigated area is affected by both natural and human-63 induced subsidence. The Po Plain is a subsiding sedimentary basin encompassed by the 64 Alps, Apennines and Dinarides Chains. Two structural environments occur within the 65 basin: the north-verging Apennine fold-and-thrust belt system that is buried under the 66 Plio-Quaternary cover and a platform gently dipping from the Alps into the basin 67 (Carminati and Martinelli, 2002). Sedimentation has filled the basin with alternate 68 stratigraphic sequences of sands, silts and clays variably interbedded and normally 69 consolidated and containing water in the form of impregnating water and groundwater 70 (Zerbini et al., 2000; 2002). These conditions are most favorable for the development of 71 both natural and anthropogenic subsidence. Long-term natural subsidence rates range 72 between 1-to-2 mm/yr (Pignone et al., 2008), with maximum rates of 2.5 mm/yr 73 evaluated from the analysis of borehole stratigraphies and from available seismic sections 74Page 4 of 60 A c c e p t e d M a n u s c r i p t 4 (Carminati et al., 2003) with the largest rates occurring in the southern part of the Po 75Plain and in the Po Delta. As discussed by Carminati and Di Donato (1999), 76 backstripping analysis suggests that tectonics accounts for about 50% of the long-term 77 natural subsiden...