Assessment of Drought Evolution in the Yangtze River Basin Based on Downscaled Grace Data

Abstract

Assessing drought characteristics and its evolution patterns in the Yangtze River Basin (YRB) holds significant implications for understanding the distribution and variability of water resources in the basin. This study employs a statistical downscaling method based on the principle of water balance to enhance the spatial resolution of the terrestrial water storage anomaly (TWSA) estimations derived from the Gravity Recovery and Climate Experiment (GRACE) into 0.1°. Utilizing the downscaled data, we establish high-precision drought indices including Water Storage Deficit (WSD) and Water Storage Deficit Index (WSDI). Furthermore, the dispersion rate of drought area (DRDA) and average WSDI in drought area (WSDIDA) are defined to access the extent of drought impact and the severity in drought-affected areas. These indicators enable the identification and analysis of drought characteristics and its spatiotemporal evolution in the YRB from April 2002 to September 2021. The main innovation results are as follows. (1) Compared with PCR-GLOBWB model, our downscaled dataset presents its excellent applicability in detecting regional drought within the YRB. The majority of test sampling points demonstrated an increase in the correlation coefficient with the reference data by approximately 0.15-0.2 compared to the downscaled premise. (2) During the study period, the YRB experienced 9 basin-wide drought events, with the most severe event lasting for 18 months and a total WSD of nearly 550 mm. Over 90% of the basin area suffered from varying degrees of drought in this event. (3) In the case of no significant trend observed in WSDIDA, DRDA within the basin is shrinking at a rate of 2.54% per year. Drought conditions in the YRB and most of its sub-basins have been effectively alleviated, as evidenced by a significant increasing trend in WSDI. (4) The Jinsha River Basin and the Han River Basin maintain a high annual drought frequency (ADF), and their DRDA, Annual Drought Duration (ADD) and Annual Drought Severity (ADS) show increasing trends, indicating that drought in the entire YRB is gradually concentrating on these two sub-basins. Our new downscaled GRACE data and proposed drought indicators have promising application prospects in assessing the local drought characteristics in the basin, providing robust support for drought prevention and scheduling decision-making in the region.

Keywords: GRACE, Downscaling, Water storage deficit index, Extent of drought impact