A novel 3D hazard assessment framework for dry-to-wet abrupt alternation events and its application in the Yangtze River Basin, China

Dry-to-Wet Abrupt Alternation (DWAA) events represent a class of successive compound extremes characterized by a rapid transition from drought to wet conditions. These events, increasing in frequency in recent years, pose significant challenges to agricultural productivity, water resource management, and ecosystem stability. While existing studies have primarily focused on the identification and statistical characterization of DWAA events, quantitative hazard assessments remain limited. In this study, we propose a novel three-dimensional Vine Copula-based hazard assessment framework integrating event strength, duration, and rapid alteration rate. Unlike traditional two-dimensional assessments, the explicit incorporation of rapid alteration rate as a third hazard dimension directly captures the abrupt nature of dry-to-wet transitions that previous approaches have not fully addressed. Using the Yangtze River Basin as a case study, the results show that western Sichuan and the middle-lower reaches are high-hazard areas, where DWAA events are more frequent, stronger, and more rapidly changing. Low-to-moderate-hazard events are more prevalent in spring, with the median hazard index for low-intensity events in spring approximately 9.3 times that of summer, and the proportion of grid cells exceeding 0.5 for medium-intensity events reaching 20.87% in spring, more than double that of autumn (9.62%); high-hazard events exhibit weak seasonal dependence and broader spatial impact. Between 2001 and 2022, joint return periods of moderate-to-extreme DWAA events have shortened significantly compared to 1980–2000, indicating intensification under climate change. This framework aligns with real-world observations and provides a scientific basis for developing targeted strategies to manage the compound risks of DWAA events. • A novel three-dimensional copula framework was developed to assess the hazard and return period of DWAA events. • The high-hazard areas in the Yangtze River Basin are located in the middle and lower reaches. • Joint return periods of moderate to extreme DWAA events shortened after 2001, indicating rising frequency under climate change.