GRACE-Derived Terrestrial Water Storage Changes in the Inter-Basin Region and Its Possible Influencing Factors: A Case Study of the Sichuan Basin, China

We investigate terrestrial water storage (TWS) changes over the Sichuan Basin and the related impacts of water variations in the adjacent basins from GRACE (Gravity Recovery and Climate Experiment), in situ river level, and precipitation data. Although GRACE shows water increased over the Sichuan Basin from January 2003 to February 2015, two heavy droughts in 2006 and 2011 have resulted in significant water deficits. Correlations of 0.74 and 0.56 were found between TWS and mean river level/precipitation within the Sichuan Basin, respectively, indicating that the Sichuan Basin TWS is influenced by both of the local rainfall and water recharge from the adjacent rivers. Moreover, water sources from the neighboring basins showed different impacts on water deficits observed by GRACE during the two severe droughts in the region. This provides valuable information for regional water management in response to serious dry conditions. Additionally, the Sichuan Basin TWS is shown to be influenced more by the Indian Ocean Dipole (IOD) than the El Nino-Southern Oscillation (ENSO), especially for the January 2003–July 2012 period with a correlation of −0.66. However, a strong positive correlation of 0.84 was found between TWS and ENSO after August 2012, which is a puzzle that needs further investigation. This study shows that the combination of other hydrological variables can provide beneficial applications of GRACE in inter-basin areas.