Enhanced Surface Coupling but Suppressed Convective Triggering During Humid–Hot Extremes in the Yangtze River Basin, a Major Humid‐Heat Hotspot in China

Abstract Compound humid‐hot extremes bring growing threats to human society, yet land–atmosphere feedbacks regulating these events remain insufficiently understood. Using high‐resolution observational and reanalysis data, we reveal that the Yangtze River Basin (YRB) is a prominent hotspot for humid‐hot extremes, with rare hot‐only events. Comparing humid‐hot and non‐humid‐hot days, we find that humid‐hot extremes are sustained by positive feedbacks involving a high‐pressure anomaly, suppressed clouds and precipitation, drier soils, enhanced evapotranspiration, and lower relative humidity—mutually reinforcing the extreme state. Land–atmosphere coupling strengthens substantially for near‐surface variables, indicating stronger land surface control. Yet this enhanced coupling does not extend to cloud development: elevated lifting condensation levels and reduced relative humidity inhibit cloud formation, leading to a decoupling between convection and cloud development and allowing humid‐hot extremes to persist. Our findings highlight the role of land surface processes in modulating compound extremes and provide a foundation for improving their prediction.