A Two-Step Linear Model to Fill the Data Gap Between GRACE and GRACE-FO Terrestrial Water Storage Anomalies

The Gravity Recovery and Climate Experiment (GRACE) and its Follow-On (GRACE-FO) missions have revolutionized global terrestrial water storage anomalies (TWSA) measurements. However, the 11-month data gap between the two GRACE missions disrupts the measurement continuity and limits its further applications. Previous attempts to fill this data gap require further improvement in terms of method robustness and product quality. Here, we propose a novel two-step linear model using precipitation, temperature data, and hydrological model-simulated TWSA as predictors to fill the 11-month data gap between the two GRACE missions and generate six global gridded GRACE-like TWSA products from April 2002 to July 2021. These products are evaluated at grid scale globally and also basin scale for the world's largest 72 river basins. Results indicate that our GRACE-like data show great consistency with the GRACE/GRACE-FO observations. While most basins exhibit consistent performance across the six GRACE-like TWSA products, certain areas with lower signal-to-noise ratios show significant variability. Furthermore, we assess the performance of our GRACE-like data during the data gap using one previous reconstruction, a hydrological model simulation, and the Swarm satellite measurement. The results confirm that our GRACE-like data exhibit equivalent performance within and outside the data gap. This study introduces a more simple and robust method for predicting the missing data between the two GRACE missions and provides readily applicable continuous GRACE-like TWSA products for hydrologic applications.