Heatwave-dominated changes in compound drought and heatwave events in the middle and lower Yangtze River Basin, China, during 1961–2020

Study region The middle and lower reaches of the Yangtze River Basin, China. Study focus Compound drought and heatwave events (CDHWs) pose increasing risks to water resources, agriculture and ecosystems, but their daily-scale evolution and amplification relative to single extremes remain insufficiently understood in humid monsoon regions. Using daily observations from 66 meteorological stations during 1961–2020, this study examined the long-term changes, periodic variability, spatial patterns and amplification characteristics of warm-season CDHWs. A regression-based relative contribution framework was further used to assess whether CDHW variability was more closely associated with heatwave- or drought-related indicators. New hydrological insights for the region Warm-season CDHWs showed a clear transition around the 1990s, with decreasing tendencies before 1990 and widespread increases thereafter. High-value and significantly increasing areas were mainly concentrated in Hubei, Hunan, Jiangxi and the Jiangsu–Zhejiang–Shanghai region. Compared with single heatwaves or droughts, CDHWs were characterised by stronger thermal stress, markedly lower precipitation and longer event duration, indicating an amplification of compound hot–dry extremes. Heatwave-related indicators showed larger relative explanatory contributions than drought-related indicators for CDHW occurrence days, event frequency and maximum duration, although drought duration and drought frequency were locally important in mountainous areas. These findings highlight the need to integrate heatwave monitoring with drought risk management to improve early warning and climate adaptation strategies in the Yangtze River Basin.