A comparison of terrestrial water storage data and multiple hydrological data in the Yangtze River basin

The monthly GRACE-based terrestrial water storage (TWS) data in upper and middle Yangtze River basin during 2002—2013 are compared with measured precipitation and discharge, and model simulated soil moisture from the aspects of temporal trend, correlation, and time lag. Four drought indices, including Standardized Water Storage Index (SWSI), Standardized Precipitation Index (SPI), Standardized Runoff Index (SRI) and Standardized Soil Moisture Index (SSMI), are used to assess the intensity and timing of drought events in the upper and middle Yangtze River basin. The results show that: TWS exhibits similar temporal variation as precipitation, discharge and soil moisture in the upper Yangtze River basin, exhibiting no significant trends, whereas TWS has the same significant upward trend as annual reservoir water storage in the middle Yangtze River basin, indicating significant impacts of human activities on TWS in the middle Yangtze River basin; the number of months with drought at various levels indicated by different drought indicators are close to each other, although not equal; the GRACE-based SWSI has poor capability to capture extreme droughts; the comparison of the timing of drought events indicated by different drought indicators shows lags between meteorological drought and hydrological drought and agricultural drought.