GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.3 GNGTS 2023 Drought-induced vertical displacements in the Po river basin (Northern Italy) from GNSS measurements F. Pintori 1 , E. Serpelloni 1 1 Istituto Nazionale di Geofisica e Vulcanologia, sez. Bologna Transient ground deformation induced by changes in hydrological fluxes has been observed in several environments, worldwide. In this work we analyze vertical ground displacement time-series from continuous global navigation satellite system (GNSS) stations located within the Po river basin, in Northern Italy, in order to measure deformation signals associated with the drought that is characterizing the Po Plain since 2021, and infer quantities and spatial distribution of water storage loss. GNSS displacement time series have been analyzed using a regularization model based on L1-norm to identify trend changes and seasonal terms. This analysis allows us to reconstruct the long-term temporal evolution of vertical ground displacement trends, which has been used as input of a principal component analysis (PCA), performed with the goal of extracting a spatially consistent signal in vertical ground displacements. The temporal evolution of the first principal component is well correlated with trend changes of the Po river level (Fig. 1). This suggests that the common, long term variations of vertical ground displacements are driven by the hydrology of the area. We invert the results of the PCA in order to estimate equivalent water height (EWH) variations, assuming a preliminary reference Earth model, focusing on the drought occurring in the study region since 2021. We estimate that, since 2021, GNSS uplift up to 7 mm are caused by EWH decrease of some decimeters, especially in the southern portions of the Po basin (Fig. 2); while in the plain the water loss seems smaller. We compare our results with the Global Land Data Assimilation System (GLDAS) model estimates of water content as soil moisture, snow and canopy water and the equivalent water level variation estimated by the Gravity Recovery and Climate Experiment (GRACE). We find that in the last two years EWH loss estimated from the GNSS data inversion is larger than what is modeled by GRACE and GLDAS. Furthermore, while GRACE spatial resolution is too coarse to observe significative EWH amplitude variations over the study region, both GLDAS and GNSS results show that water loss has been larger in the southern part of the basin, which correspond to the Apennines mountain chain, than in the plain. On the other hand, the agreement between GLDAS and GNSS results is reduced when observing the distribution of the water loss variation in the north-western part of the basin, where the Alps are located. Taking advantage of a dense network of continuous GNSS stations, our results show that multi-year changes in water storage can be effectively monitored both in terms of temporal evolution and spatial distribution using space geodetic measurements, without the need of relying only on large