Will the 2022 compound heatwaveedrought extreme over the Yangtze River Basin become Grey Rhino in the future?

The increasingly frequent and severe regional-scale compound heatwave-drought extreme events(CHDEs),driven by global warming,present formidable challenges to ecosystems,residential livelihoods,and economic conditions.However,uncertainty persists regarding the future trend of CHDEs and their insights into regional spatiotemporal heterogeneity.By integrating daily meteorological data from observations in 1961-2022 and global climate models(GCMs)based on the Shared Socioeconomic Pathways,the evolution patterns of CHDEs were compared and examined among three sub-catchments of the Yangtze River Basin,and the return periods of CHDE in 2050s and 210Os were projected.The findings indicate that the climate during the 2022 CHDE period was the warmest and driest recorded in 1961-2022,with precipitation less than 154.5 mm and a mean daily maximum temperature 3.4°C higher than the average of 1981-2010,whereas the char-acteristics in the sub-catchments exhibited temporal and spatial variation.In July-August 2022,the most notable feature of CHDE was its extremeness since 1961,with return periods of~200-year in upstream,80-year in midstream,and 40-year in downstream,respectively.By 2050,the return periods witnessed 2022 CHDE would likely be reduced by one-third.Looking towards 2100,under the highest emission scenario of SSP585,it was projected to substantially increase the frequency of CHDEs,with return periods reduced to one-third in the upstream and downstream,as well as halved in the midstream.These findings provide valuable insights into the changing risks associated with forthcoming climate extremes,emphasizing the urgency of addressing these challenges in regional management and sustainable development.

A New Method to Identify the Maximum Time Interval between Individual Events in Compound Rainstorm and Heatwave Events

Growing evidence indicates that extreme heat and rain may occur in succession within short time periods and cause greater impacts than individual events separated in time and space.Therefore,many studies have examined the impacts of compound hazard events on the social-ecological system at various scales.The definition of compound events is fundamental for such research.However,there are no existing studies that support the determination of time interval between individual events of a compound rainstorm and heatwave(CRH)event,which consists of two or more potentially qualifying component heatwave and rainstorm events.To address the deficiency in defining what individual events can constitute a CRH event,this study proposed a novel method to determine the maximum time interval for CRH events through the change in CRH event frequency with increasing time interval between individual events,using southern China as a case study.The results show that the threshold identified by the proposed method is reasonable.For more than 90%of the meteorological stations,the frequency of CRH events has reached a maximum when the time interval is less than or equal to the threshold.This study can aid in time interval selection,which is an important step for subsequent study of CRH events.