Flood Evolution in the Past 60 Years Revealed by Reconstructed Daily Terrestrial Water Storage Anomalies in China

The Gravity Recovery and Climate Experiment (GRACE) satellites and its successor mission, the GRACE Follow-On (GRACE-FO) satellites provide a unique capability to monitor terrestrial water storage anomalies (TWSA) and key hydrological variables associated with flood events. However, GRACE data is only available from 2002 onwards, which poses challenges for long-term studies of terrestrial water storage and flooding. Additionally, the monthly temporal resolution of GRACE (-FO) data limits its utility for detailed flood studies on finer time scales. Against these issues, this study employed a statistical model to reconstruct daily TWSA on a grid scale in China from 1963 to 2022. Considering that flood events have three-dimensional spatiotemporal characteristics, this study identified 359 flood events that occurred in China between 1963 and 2022 using a three-dimensional Image-CONnectivity based FLOOD identification (ICON-FLOOD) approach, combined with Normalized Daily Flood Potential Index (NDFPI) calculated from reconstructed daily TWSA and surface runoff. The spatiotemporal variations characteristics of flood events in China over the past 60 years were also analyzed. The results show that 60 flood events that were not recorded in these three disaster databases but actually occurred were detected. The average duration, intensity, and affected area have experienced an “increase-decrease-increase-decrease-increase” process. Notably, in the past 20 years, the duration, intensity, and affected area of flood events are increasing. The methods and findings of this study may provide valuable references for flood risk management and mechanism analysis.