Analysis on weather background for 1998 heavy flood in the Yangtze River Valley

In the main flood season in 1998, the west Pacific subtropical high was deviated to the south and was much stronger than usual for a long time, and stable blocking pattern was persistent in the middle and high latitudes in the Northern Hemisphere. As a result, the rain belt paced up and down over Dongting and Poyang Lake water systems during June and July, which led to severe flooding in the middle and lower Yangtze River. In August, with the subtropical high migrating to the north and the west, heavy rain processes occurred in the upper Yangtze. Due to the fact that the peak floods from the upper reaches were rushing downstream and the floods on the middle and lower reaches were jacked up, flood stages on the main stem remained high for a long time. Flood stages at most hydrometrical stations on the main stem exceeded the corresponding historical records. The 1998 flood was a new type of heavy flood on the Yangtze River.