Tracking the warning signal of extreme rainstorm and flood events in Haihe River Basin through historical documents

The available instrumental meteorological data spans less than a century, which is insufficient to robustly diagnose the mechanisms of extreme event occurrences. In this study, historical documents were used to identify extreme rainstorm-flood events in the Haihe River Basin (HRB) from 1736 to 1911, including their occurrence periods, affected areas, and rainfall characteristics. Moreover, early warning signals and climatic conditions associated with severe rainstorm-flood occurrences were disucssed. The findings indicate that, due to terrain uplift, the majority of severe floods in the HRB predominantly occurred in the piedmont plains of the Taihang Mountains. In particular, the landfall of long-distance typhoons along China’s southern coast, combined with the northward intensification of the western Pacific subtropical high, served as preconditions for these flood events. Accompanied by a significant increase in easterly and southeasterly winds, water vapor from the western Pacific Ocean and the South China Sea entered the North China Plain through double jet streams from the southeast and southwest. The majority of these floods occurred during La Niña years. Typhoon landfall, the strengthening of the northward movement of the western Pacific subtropical high, and La Niña events serve as key early warning signals for extreme rainfall and flooding, which are essential for disaster prevention and mitigation in the HRB.