Monitoring groundwater changes in the Yangtze River basin using satellite and model data

Space-borne geodetic sensors and model-based datasets have been used to monitor groundwater changes in the Yangtze River basin (YRB). Groundwater storage variations were computed using the following datasets: • Gravity Recovery and Climate Experiment (GRACE)-derived terrestrial water storage (TWS), • Noah driven Global Land Data Assimilation System (GLDAS-Noah) model to simulate the total water content (TWC) i.e. soil moisture, ice and snow, and canopy water storage, and • Satellite altimetry-observed surface water reservoir storages. Overall, the results show that groundwater in the YRB rose by at least 3.34 km 3 /yr between January 2003 and December 2009. However, the estimated groundwater linear trend for the period of 2003–2009 was −0.95 km 3 /yr according to the Changjiang and Southwest Rivers Water Resource Bulletin (CJSRWB). An analysis of the methodology of the CJSRWB shows that the groundwater estimate was based on the water balance approach, which has been found to be weak in inter-basin sub-surface flow. The GRACE-estimated groundwater rise is larger and suggests that the YRB is affected by seepage from Tibetan lakes through a sub-surface fault. Additionally, there is evidence showing that water loss from the Yangtze River by underground leakage through faults could also be a cause of the difference. Therefore, it is concluded that further investigation is required to determine the causation.