Long-term temporal-scales of hydrosphere changes observed by GPS over Europe: a comparison with GRACE and ENSO

Hydrogeodesy can benefit greatly from the use of Global Positioning System (GPS) displacements to analyse local changes in the hydrosphere, which the commonly used Gravity Recovery and Climate Experiment (GRACE) mission is unable to provide due to coarse spatial resolution. Hydrosphere changes recorded by GPS are unfortunately hidden among the other signals to which the system is also sensitive so that the sensitivity of GPS to changes in the hydrosphere on temporal-scales from pluri-annual to decadal is questionable. We focus on hydrosphere signatures present on these long-term temporal-scales as observed by GPS through the vertical displacement time series (DTS) of 122 permanent stations over Europe and compare them to the DTS derived from GRACE for GPS locations. Our methodology is based on the weighted Savitzky-Golay (S-G) filter, an underestimated filter in the field of geodetic time series analysis. We show that the correspondence between GPS and GRACE on long-term temporal-scales is generally strong, but decreases for coastal regions and regions where the coarse gridding of GRACE does not capture local hydrosphere effects. Further, the negative correlation with El Ni\~no Southern Oscillations (ENSO) is confirmed for Europe.