Increasingly frequent and severe dry-to-wet abrupt alteration events are striking the Yangtze River Basin in China

Dry-to-wet abrupt alteration events (DWAA) are characterized by the rapid transition from drought to heavy rainfall, with serious impacts on agricultural production and society in the Yangtze River Basin (YRB). However, a key research gap is the lack of comprehensive DWAA identification methods to accurately capture short-term DWAA features. Here, an improved pentad-scale DWAA index combining standardized soil moisture indexes and standardized precipitation indexes is proposed and the temporal and spatial characteristics of DWAA are identified using ERA5-Land reanalysis data. The results show that, from 1980 to 2022, the average of frequency, duration, strength, and rate of rapid alteration of DWAA in the YRB have significantly increased. Compared with the 1980s, the average duration of DWAA extended from 6.2 pentads to 6.3 pentads in the 2010s, and the average rapid alteration rate increased from 2.8 pentad- 1 to 2.9 pentad(-1). High occurrence areas of DWAA (20 times) were observed in east and south of the YRB and northwestern Sichuan. These regions also experienced prolonged duration of up to 13 pentads and great strength of 17. Based on the Cumulative Distribution Function and Copula function, the average state of DWAA (50th percentile, duration of 5 pentads, strength of 8.2) had a recurrence period of 1 year, while extreme state events (90th percentile, duration of 9 pentads, strength of 15.1) had a recurrence period of 90 years. These findings can provide an important scientific basis for local governments to improve the regional responding capacity and development of disaster prevention and mitigation policies.