High Spatial Resolution of GRACE-Derived Ice Mass Change Reveals Glacier-Scale Mass Loss in Greenland Ice Sheet

The Gravity Recovery and Climate Experiment (GRACE) and its follower GRACE-Follow On (GRACE-FO) act as a reliable tool to detect the Earth's surface mass change. However, its discontinuity between GRACE and GRACE-FO limits its applicability for long term analysis. Its coarse spatial resolution (∼300 km) of GRACE and GRACE-FO (GRACE/GFO) hampers detailed understanding of ice mass change response mechanisms to climate change at spatial scales below 200,000 km2. Additionally, researches in downscaling GRACE-derived ice mass change in the Greenland ice sheet (GrIS) remains limited. Based on the continuous reconstructed GRACE/GFO data, we firstly compared the performance of geographically weighted regression (GWR) and random forest (RF) to downscale GRACE/GFO from 0.25°×0.25° to 5 km×5 km at a spatial global scale (SGS) in GrIS. This study presents the first application of such high-resolution downscaling to the reconstructed GRACE/GFO results over the GrIS. Finally, the SGS-GWR outperformed SGS-RF in capturing reasonable and finer signals of ice mass change. And downscaled results from SGS-GWR fit well with original GRACE/GFO mascon solutions and other independent estimates, achieving mean correlation coefficients and mean root mean square error at 0.98/2.68 cm by considering the nonstationarity heterogeneity of variables. Based on the continuous and high-resolution ice mass change, glacier-scale analysis of climatic forcing mechanisms, such as Greenland Blocking through its modulation of runoff, snowfall, rainfall, and solid ice discharge in 2012 and 2019, represents a novel contribution.