Investigating Terrestrial Water Storage Changes and Their Driving Factors in the Southwest River Basin of China Using Geodetic Data

The space geodetic technologies [e.g., global navigation satellite system (GNSS) and Gravity Recovery and Climate Experiment (GRACE)/GRACE Follow-on (GFO)] provide effective tools to infer terrestrial water storage (TWS) change, which is an important indicator of the hydrological cycle and climate change. This study investigated the optimization approaches of the Slepian basis function (SBF) method in recovering TWS changes in the Southwest River Basin of China (SWRB) with sparse data and conducted a comprehensive analysis of TWS changes in SWRB using GNSS and GRACE/GFO. The results show that using the Shannon number criterion and even-distributed GNSS observations can obtain reliable TWS changes based on the SBF method. The GNSS-inverted TWS changes generally maintain good consistency with GRACE/GFO and hydrological model results in SWRB, but the ground-based daily GNSS estimates present stronger signal amplitudes and more high-frequency information. In the upper SWRB, the GRACE/GFO well reveals the continuous water loss (-8.19 +/- 1.76 mm/yr) induced by human activity, while the GNSS does not reveal the long-term linear changes of TWS, because it is difficult to separate them from the GNSS vertical displacement time series. In the lower SWRB, both GNSS and GRACE/GFO can reveal the increasing and decreasing trends of TWS changes within the study period, and precipitation is the dominant driving factor that causes the secular changes in TWS. In addition, the ENSO generally presents relatively stronger effects on TWS changes than PDO in SWRB. Our results contribute to understanding the regional hydrological cycle and managing the water resources in SWRB using geodetic data such as GNSS and GRACE/GFO.