Drought and Flood Characterization and Connection to Climate Variability in the Pearl River Basin in Southern China Using Long-Term GRACE and Reanalysis Data: the role of reservoir storage change

Abstract

Since the launch of the Gravity Recovery And Climate Recovery (GRACE) satellites in 2002, many new methods have been developed for assessing drought severity and flood potential. Meanwhile, the development of global reanalysis systems enables long-term drought and flood monitoring and evaluation. A few previous studies on assessing drought severity and flood potential using GRACE-based or MERRA-2 reanalysis total water storage (TWS) change data (1) examine the accuracy of both GRACE and reanalysis data, (2) quantify the contribution of reservoir storage to drought severity and flood potential, (3) analyze the impact of reservoir storage regulation on the response of drought severity and flood potential to climate change. Taking the Pearl River Basin as an example, this study investigated the above three scientific questions, and explored the impact of climate system on drought and flood occurrences. The major findings are as follows: (1) Large uncertainties still exist on quantifying drought severity using GRACE-based TWS change data. (2) The historical MERRA-2 TWS change data before the 21 century in the Pearl River Basin are unreliable for drought and flood assessment. (3) The inclusion of reservoir storage results in longer (shorter) drought duration and overestimated (underestimated) drought severity before (after) reservoir impoundment. (4) GRACE is capable to detecting sub-basin scale flood in the Pearl River Basin. However, the actual flood potential after reservoir impoundment is overestimated using GRACE-based data if reservoirs storage is not removed. (5) Reservoir storage regulation modulates the response of TWS anomaly to Pacific Decadal Oscillation. (6) El Niño–Southern Oscillation strongly influences precipitation and TWS anomalies in the Pearl River Basin through East Asia monsoon. (7) Evidences are found on the asymmetric impacts of El Niño and La Niña on rainfall under the East Asian climate system. (8) The drought severity is intensifying in the Pearl River Basin over the last four decades. This study has broad implications for drought and flood assessment worldwide. Future studies on assessing drought severity and flood potential, and on climate-human interaction using satellite and reanalysis data should examine the data reliability and quantify reservoir storage contribution.