Decadal Variability of Rainfall Persistence Time and Rainbelt Shift over Eastern China in Recent 40 Years

Using observations of precipitation from rain gauge stations in China for the period of 1960—1999 and the monthly European Center for Medium-Range Weather Forecast reanalysis for the period from 1958 to 2001, the variations of the beginning and ending time of the rainfall and rainbelt shift over eastern China between the cold and warm periods of globally averaged surface air temperatures are examined. The associated atmospheric circulation over East Asia is also analyzed. The results show that in recent 40 years, the relative cold period of the surface air temperature appears in the 1960s and 1970s, while the warm period appears in the 1980s and 1990s. Compared to the cold period, the annual total rainfall in the warm period is characterized by the feature of southern floods/northern droughts, namely that the annual total rainfall increases along the valley of the Yangtze River in the warm period and decreases over North China. The increase in the valley is mainly due to the increase of rainfall in summer (June to August) and March, while the decrease is attributed to the decrease from July to September. On the average, the persistent heavy rainfall over southern China (25°—30°N, 115°—120°E) begins earlier, ends later, and maintains longer in the warm period than in the cold period. Over northern China (34°—40°N, 115°—120°E), the persistent heavy rainfall begins later and maintains shorter in the warm period. Moreover, there is a significant difference in the rainbelt shift over eastern China from late spring to summer between the cold and warm periods. In the cold period, the rainbelt shift shows a pronounced feature from South China via the valley of the Yangtze River to North China. However, in the warm period, the rainbelt mainly appears along the valley, not showing a striking shift from South China to North China. The southern floods/northern droughts over eastern China are associated with anomalies of the East Asian atmospheric circulation under global warming. In the warm period, the low over the Asian continent and the high over the Sea of Okhotsk are strong during summer, accompanied by the anomalous northeasterlies from the south of the Sea of Okhotsk to mid-latitudes of East Asia, which may strengthen the activities of cold air at these latitudes. Meanwhile, the subtropical high over the western North Pacific is more northward in the warm period. Corresponding to these anomalies, the East Asia summer subtropical monsoon weakens and the Meiyu front strengthens along the valley of the Yangtze River, which makes the rainfall stay in the valley, resulting in the increase of local rainfall. Anomalous downward motions appear over northern China, resulting in the decrease of local rain.