GNSS observations of the surface water storage-induced displacements in the Eifel area, NW Europe: the influence of the Rhine river

The Earth's surface undergoes deformations due to temporal variations in the distribution of atmospheric, hydrological and oceanic mass loads on the lithosphere. These deformations can be observed using Global Navigation Satellite System (GNSS) data where seasonal variations are particularly prominent in GNSS height time series.

While continental-scale water mass redistributions can be captured by Gravity Recovery and Climate Experiment/Follow On (GRACE/FO) or global hydrological models, surface water storage changes e.g. those caused by rivers and lakes cannot be resolved. However, GNSS timeseries may contain these small-scale surface water loading signals especially when located close to water bodies. Correctly representing such close-range, subgrid-scale loading signals is important for interpreting GNSS displacements, in particular when the goal is validating hydrological models.

In this study, we compiled daily time series from 326 GNSS stations jointly with water level observations along the Rhine river in the the Eifel area, North West Europe. The GNSS time series underwent careful post-processing including offset corrections and outlier removal. We identified a statistical relationship between the annual GNSS amplitudes and the stations' distance from the Rhine River. After applying blind source separation techniques, including Singular Spectrum Analysis (SSA) and hydrological model-based corrections (using the Community Land Model version 5, CLM5, at daily resolution) to isolate large-scale common mode signals from the GNSS observations, the correlation between the residual GNSS signals and Rhine river level variations improved. We further inverted for regional elastic Earth parameters based on a half-space infinite elastic Earth model to estimate the surface water induced vertical displacements. The results demonstrated that surface water loading could account for a considerable fraction of the vertical displacement observed at GNSS stations near the riverbanks on daily to monthly timescales.