Assessment of hydrological drought and its recovery time for eight tributaries of the Yangtze River (China) based on downscaled GRACE data

Hydrological drought is increasing under the impact of global change, which could have serious influences on the stability of ecological systems and water-dependent human activities in the affected regions. In this study, the total water storage (TWS) derived from the Gravity Recovery and Climate Experiment (GRACE) satellites from 2003 to 2012 was downscaled to a finer resolution by incorporating the output from a land surface model. The downscaled data was used to identify hydrological drought for eight tributaries of the Yangtze River in China. The trend in the water storage deficit based on the downscaled GRACE data ranged from -0.86 to 0.29 mm month(-1) for the eight tributaries from 2003 to 2012, among which the absolute largest value occurred in the Poyang Lake Basin. The eight tributaries experienced between four and seven hydrological droughts during the study period, and droughts in 2003, 2006 and 2011 occurred in all of the tributaries. The drought recovery rate for the eight tributaries was between 4.5 and 7.2 mm month(-1), and the average drought recovery time was between 3.6 and 5.7 months. Tributaries with a high climate moisture index had low frequencies of drought occurrence but had long drought durations and large drought severities, resulting in long drought recovery times. Additionally, the impacts of human activity on hydrologic processes intensified significantly from 2003 to 2012, such as water storage in reservoirs and water consumption, leading to spatial differences in regional drought characterizations. The results are useful for the understanding of the mechanism of hydrological drought formation and the extension of GRACE applications in medium and small-scale catchments.