Water Storage Variations and Drought Propagation in Southern Europe With Additional Constraints of GNSS Horizontal Displacements

Global Navigation Satellite System (GNSS) displacements are widely used to recover regional terrestrial water storage (TWS) variations. Most previous studies focused on using GNSS vertical displacements (GNSS-VDs) and ignored the horizontal components. Given the important information from GNSS horizontal displacements (GNSS-HDs), we integrate both GNSS vertical and horizontal displacements (GNSS-VHDs) to infer daily TWS variations in southern Europe from January 2011 to December 2022. Our results show that the variations of TWS derived from GNSS are consistent with Gravity Recovery and Climate Experiment (GRACE)/GRACE Follow-On (GFO) in the spatiotemporal domain. The root-mean-square error (RMSE) of the TWS time series between GNSS inversion and GRACE/GFO is reduced from 36.5 to 34.3 mm by incorporating the horizontal displacements, revealing an improvement in TWS estimation. We explore the propagation time from meteorological drought to hydrological drought in southern Europe and its driving factors. Results suggest that the propagation time varies from 0 to 7 months, with an average time of 1.6 months. Further analysis shows that the drought propagation time (DPT) is significantly affected by precipitation. It is also found that evapotranspiration dominates the TWS cyclic processes in southern Europe. An approximately 1.7-year interannual periodic TWS signal is detected, which is attributed to the Arctic Oscillation (AO). This study provides an enhanced inversion of TWS variation with additional constraints of GNSS-HDs for the in-depth investigation of drought propagation in southern Europe.