Interannual variations in GNSS vertical displacement related to snow depth: A case study at Tateyama Murodo, Toyama, Japan (2006–2023)

Redistribution of surface mass associated with atmospheric pressure, ocean tides, land water storage, and snow causes elastic deformation of the Earth's crust that can be detected by the Global Navigation Satellite System (GNSS). In Japan, seasonal snow accumulation is one of the dominant sources of surface mass loading and produces vertical GNSS displacements of several centimeters, particularly in mountainous regions with heavy snowfall. However, quantitative comparisons between GNSS-derived vertical deformation and direct observations of local snow depth remain limited, and most previous studies have focused mainly on the mean seasonal cycle rather than interannual variability. In the present study, we investigate the relationship between GNSS vertical displacement and interannual variations in snow depth in the Tateyama Murodo area of the Northern Japan Alps, one of the snowiest regions in Japan. Daily GNSS positions from GEONET station 041138 for the period 2006-2023 were analyzed using precise point positioning with ambiguity resolution (PPP-AR). Deformation caused by atmospheric loading, non-snow land water storage, and non-tidal ocean loading was calculated using global loading models and removed from the GNSS time series, together with long-term tectonic deformation. The residual signal was then compared with snow depth observations obtained from annual snow surveys conducted near the GNSS station. After removing other loading components, the GNSS vertical displacement exhibits seasonal amplitudes of approximately 2.4-3.9 cm and shows a clear correlation with observed snow depth, with deeper snow corresponding to larger subsidence. Similar seasonal variations were also observed at nearby GNSS station J470, located about 900 m away, indicating that the signal primarily reflects regional snow loading. Both linear and quadratic relationships adequately explain the observations. These results demonstrate that GNSS vertical displacement records interannual variations in snow loading and suggest that GNSS observations can provide a quantitative proxy for seasonal snow accumulation in alpine regions.