Classification and contribution of compound rainstorm and heatwave hazards in southern China

ABSTRACT Compound extreme events, including extreme wet conditions and extreme heat, exhibit distinct temporal sequences, yet their characteristic differences remain systematically understudied. In this study, we attempt to reveal the main types and dominant factors affecting compound rainstorm and heatwave (CRH) events in the southern region of China. Firstly, we define CRH events and then classify them into two categories (binary and multiple) according to the number of individual events. Then, we analyze the spatiotemporal changes in the frequency of each kind of CRH event during the period from 1981 to 2020. Finally, the contribution of heatwaves and rainstorms to CRH events and to the frequency change is assessed. The results show that CRH events mostly occurred in southeast China and eastern Sichuan. The contribution of heatwaves is larger for most multiple CRH, while heatwaves and rainstorms contributed equally for most rainstorm–heatwave events. In addition, the frequencies of binary CRH events increased rapidly after 2000. Heatwaves are the main dominant factor leading to the rapid increase in the frequency of CRH events. The results help improve our understanding of the combination of rainstorms and heatwaves and provide a justification for studying compound climatic hazards.