The glacier changes in the Alps from the GRACE and GRACE Follow-On Missions

In this work, the time-variable gravity field data from the Gravity Recovery and Climate Experiment (GRACE) and GRACE Follow-On (GRACE-FO) covering the period from April 2002 to September 2023 is used to quantify glacier mass changes in the Alps. We employ a new method that utilizes the vertical surface displacement data to correct the glacial isostatic adjustment (GIA) and tectonic uplift signal. This approach reveals that the mass increases caused by vertical deformation signals with a trend of 0.75 ± 0.11 Gt/yr. We further include two hydrology models Global Land Data Assimilation System (GLDAS) and WaterGAP Global Hydrological Model (WGHM) to correct for hydrological signals in the Alps. Three forward modeling-derived schemes are used 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 (WGMS), indicate that among the three experiment 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 -2.54 ± 0.82 Gt/yr using GRACE Level-2 data and -3.42 ± 0.56 Gt/yr using the JPL Mass Concentration (Mascon) solutions. Additionally, our study identifies a three-month lag between land surface temperature and glacier mass variations, which supports the validity of our estimated glacier mass changes.