Abstract:Basic characteristics of the Meiyu over the middle lower reaches of Yangtze River in 1961-2011 are investigated by using the updated precipitation data, especially for the new features in the 21st century. The results indicate both the length of Meiyu period and rainy days reduce in recent decade, and the Meiyu amount also decreases. This change could be attributed to the negative Pacific Decadal Oscillation (PDO) and the increased frequency of the La Nina events in the 21st century. Under the negative PDO phase, rainfall above normal always occurs in northern China, especially in the regions north of the Huaihe River Valley. As a result of the more frequent La Nina events, the SSTs over the western Pacific warmer pool increase in recent decade and force the western Pacific subtropical high to be stronger and more westward and northward. Thus the warmer and wetter southwesterly moisture over the Bay of Bengal and the tropical Indian Ocean has been transported to the regions north of the Huahe River Valley instead of the Meiyu areas. This is a possible cause of the decrease of the Meiyu in the 21st century.