The Glacier Changes in the Alps From the GRACE and GRACE Follow-On Missions (2002–2023)

In this paper, time-variable gravity field data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) missions are used to quantify glacier mass changes in the Alps from 2002 to 2023. We employ a new method that utilizes the vertical surface displacement data to correct the glacial isostatic adjustment and tectonic uplift signals. This approach increases the mass change signal by 0.8 ± 0.1 Gt/yr. We further include two land hydrology models, Global Land Data Assimilation System Version 2.1 (GLDAS V2.1) and the land component of the Fifth Generation European Reanalysis (ERA5-Land), to correct the gravity data for hydrological signals. We demonstrate three different forward modeling-derived schemes to recover the signals from GRACE/GRACE-FO observations. Our results, when compared with the annual glacier mass balance from the World Glacier Monitoring Service, indicate that among the three experimental schemes, the global unconstrained forward modeling algorithm demonstrates the best performance in estimating glacier mass change in the Alps. Overall, applying our new vertical deformation correction method, we find that the total glacier mass loss rate in the Alps is −2.4 ± 0.8 Gt/yr using GRACE/GRACE-FO Level-2 data. Our results identify a 3-month lag between land surface temperature and glacier mass variations, which is related to the response of glacier melt and accumulation to temperature variations.