Monitoring of Terrestrial Water Storage Variations and Floods in Sichuan Province Using GNSS and GRACE

Continuous and dense GNSS stations can accurately measure the monsoonal precipitable water (PWV) and vertical crustal displacement caused by the hydrological load on a small scale. The Gravity Recovery and Climate Experiment (GRACE) time-varying gravity field data can accurately and effectively retrieve the changes of medium and long-scale terrestrial water storage variations. Sichuan Province is an important industrial and agricultural production base in China, where meteorological disasters such as drought and flood often occur. Monitoring terrestrial water storage variations can play a significant role in human production activities in the region. To analyze terrestrial water storage variations in Sichuan, GNSS data (PWV and vertical displacement) from 2016 to 2018 are used with the changes of vertical displacement and terrestrial water storage variations of GRACE, the TWS changes of GLDAS and the surface precipitation data. Due to data gaps in the GRACE satellite, GNSS data are combined with GRACE to monitor flood disasters. The results show that the spatial distribution and seasonal characteristics of GNSS-derived mass change time series are consistent with the results of GRACE/GRACE Follow-On satellite observations, especially in the areas with dense GNSS stations. The FPI (Flood Potential Index) calculated by GRACE TWSA (Terrestrial Water Storage Anomaly) can accurately reflect the flood events in Sichuan. Furthermore, there is a strong correlation between GNSS vertical displacement and FPI index. It is verified that the combination can effectively monitor flood events.