Hydro-gravimetry as a monitoring solution for water and ice storage changes in dynamic alpine environments

Climate change is rapidly impacting the mountain hydrosphere and cryosphere. Permafrost degradation and decreasing snow accumulation are rapidly altering the hydrological dynamics of headwater catchments with increasing dependence on subsurface water resources. Groundwater and subsurface ice are critical hydrological compartments for the resilience of alpine hydrological systems. While their buffering capacities are known to ensure perennial streamflow during increasingly long warm and dry periods, the limits of these resources are not generally understood. In spite of this growing importance, storage changes of subsurface water, in both solid and liquid form, remain the most uncertain components in alpine hydrological investigations.

Time-lapse gravimetry (TLG) involves the measurement and analysis of temporal variations in acceleration due to gravity (Δg). This hydrogeophysical method is spatially integrative, portable, and non-invasive. Because it is sensitive to all mass distribution changes, TLG is a powerful tool to fill the hydrogeological and cryospheric monitoring void in alpine settings.

Here, we present ongoing investigations of changes in groundwater storage and ground ice at multiple sites in the Swiss Alps and Pre-Alps. At the pre-alpine Röthenbach catchment, we are performing monthly TLG surveys. Preliminary results show significant spatial variability in groundwater storage changes, undetectable by piezometers and wells [see abstract EGU25-11997]. These data are being used to inform the development of a numerical hydrogravimetric data assimilation framework [EGU25-7128]. In the non-glaciated Vallon de Réchy, we have monitored seasonal decreases in groundwater storage across three summer/autumn periods, showing significant spatial and inter-annual variability and informing new conceptual models. Finally, at the Murtèl rock glacier, we recently deployed TLG, coupled with UAV imagery, to measure seasonal thaw in the active layer [EGU25-6793]. The results of this novel application were consistent with point observations and revealed spatially-variable thaw. Additionally, through comparison with a historic (1991) gravimetric survey, we found evidence of long-term permafrost degradation.

Our results, which provide quantitative, and spatially-distributed information on storage changes in groundwater and ground ice, demonstrate the significant potential of TLG for hydrogeology and cryospheric sciences.