Refined GRACE/GFO-Derived Terrestrial Water Storage Anomaly in Middle East Recovered by ICA-Based Forward Modeling Approach

The Gravity Recovery and Climate Experiment (GRACE) mission and its successor, GRACE Follow-On (GFO), effectively monitor terrestrial water storage anomaly (TWSA). However, their constrained spatial resolution imposes limitations, with leakage and attenuation potentially impacting the accuracy of regional TWSA. While GRACE/GFO observations capture the ongoing TWSA decline in the Middle East due to excessive groundwater extraction, the nearby Caspian Sea's long-term water loss, combined with the seasonal signals from the coastal sea, complicate accurate TWSA estimation through signal attenuation and leakage. To address these issues, we propose a combined approach, that is, independent component analysis (ICA)-based forward modeling (IFM), to discern and isolate the leakage effect and improve the recovery of TWSA signal. We demonstrate the impact of signal attenuation and leakage through simulation, and validate the effectiveness of IFM. This method is also confirmed through steric-corrected altimetry estimates in the Caspian Sea, Red Sea, and Persian Gulf, and further validated in Greenland and Victoria Lake. Our results show considerable leakage in GRACE/GFO TWSA estimates for Saudi Arabia and Iran. Leakage from the Red Sea and Persian Gulf introduces a 28.6% bias in Saudi Arabia's TWSA trend, while leakage from the Caspian Sea results in a 36.4% bias in Iran. After IFM recovery, the TWSA decline rates for Saudi Arabia, Iraq, and Iran are 11.48 ± 0.32, 3.56 ± 0.44, and 7.75 ± 0.45 km³/yr, respectively. This study demonstrates the effectiveness of IFM in deriving refined TWSA signal, providing valuable insights for water resource management in arid regions.