Seasonal signals in GNSS vertical displacement time series may contain a substantial contribution from surface mass loading and therefore affect the interpretation of crustal motion. This study evaluates the annual hydrological loading signal at permanent GNSS stations of the GeoTerrace network in Western Ukraine. GNSS vertical time series corrected for non-tidal atmospheric and ocean loading were compared with modelled hydrological loading displacements. Annual amplitudes and phases were estimated using harmonic analysis. The final comparison included 34 stations with sufficient common GNSS and loading epochs. GNSS annual amplitudes range from 4.42 to 10.28 mm, whereas modelled hydrological amplitudes range from 3.69 to 4.48 mm. At 24 stations, the difference between the GNSS and hydrological annual maxima is less than 15 days. Hydrological loading correction reduces the annual amplitude at 33 stations, with a median reduction of 56.1%. The absolute phase difference and amplitude reduction show a strong inverse relationship. The results indicate that the model reproduces the timing of seasonal deformation better than its full amplitude and confirm the importance of amplitude–phase analysis for geodynamic interpretation of GNSS vertical displacements.
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