A Causal Effect Network Analysis of Summer Compound Heatwave and Drought Events Over the Yangtze River Basin

Under global warming, compound heatwave and drought events (CHDEs) have become increasingly frequent. Although large‐scale atmospheric circulation and land–atmosphere feedback are recognized as the primary drivers of CHDEs, the strengths of their causal relationships and long‐term evolution remain poorly quantified. Focusing on summer CHDEs over the Yangtze River Basin (YRB) during 1961–2022, this study uses the ERA5 reanalysis data set and the Peter and Clark Momentary Conditional Independence (PCMCI) causal discovery method to construct causal effect networks for both individual extreme events and CHDEs, and quantitatively investigates the strengths and long‐term evolution of the identified causal pathways. The results show that large‐scale circulation anomalies not only directly promote regional warming but also induce soil drying, providing a favorable large‐scale atmospheric background for CHDEs. Soil moisture (SM) maintains drought conditions through a pronounced memory effect and further enhances near‐surface warming via land–atmosphere feedback, resulting in stronger atmosphere–land coupling during compound events than during individual heat events. Accordingly, both circulation anomalies and SM deficits are stronger in CHDEs than in individual heat events. Long‐term analysis shows that large‐scale circulation has remained the dominant and relatively stable driver of regional heat extremes and CHDEs, whereas the influence of SM on temperature has strengthened significantly, with the enhancement during compound events being approximately twice that for individual extreme events. This strengthening is associated with declining SM, suppressed evapotranspiration, and an enhanced conversion of net radiation from latent to sensible heat flux over the YRB.