Heavy Rain Variation Characteristics in Flood Seasons in the Middle and Lower Reaches of Yangtze River in the Last 50 Years

Based on the daily precipitation dataset archived in China Meteorology Administration during 1960－2008, interannual and decadal variations of heavy rain events in flood seasons in the middle and lower reaches of the Yangtze River as well as their trends are analysed. The results suggest that, on the interannual timescale, both the occurrence and intensity of heavy rain events display a variation with two types of periods, a quasibiennial one and a nearly 6－8-year one. On the interdecadal timescale, a nearly 12－14-year period is revealed. Particularly, there was less occurrence during the period through the 1960s to the 1980s, which was followed by more occurrence in the 1990s. Since the beginning of the 21st century, the occurrence of the events is becoming less again, albeit an occurrence increases in the northern boundary of the region, i.e., northern part of Jiangsu and Anhui provinces. The modest shift of heavy rain events to the north is in agreement with the northward shift of climatological seasonal rain band after the end of the 20th century, which was found recently. The trend analysis shows an increase in the occurrence of the events and the seasonal accumulated rainfall due to the events, albeit an insignificant decrease of the intensity of the events.