过去 300 a 长江中下游异常丰梅事件变化与洪涝灾害.

The flood disasters caused a great loss of life and property in Yangtze River Basin during June-July of 2016. Meiyu became one of the main causes of flood disasters due to the frequency, long duration and high intensity. In this study, chronology of extreme Meiyu events since 1736 was reconstructed derived from Chinese historical documents and the observational data. Furthermore, the long-term variation characteristics of extreme Meiyu events and relationships between extreme Meiyu and El Niño events were analyzed. The general circulation patterns were diagnosed to explain how El Niño influenced extreme Meiyu. The results show that there were 44 extreme Meiyu events (including 21 mega-Meiyu events) from 1736 to 2016.The most frequent occurrences of extreme Meiyu events were detected during 1901-1920 and 1991-2000. There were 21 mega-Meiyu events over the past 300 years, and the intensity was similar to that of 2016. It is found that the closely corresponding relationships existed between extreme Meiyu events and El Niño in this period. For example, 37 of total 44 extreme Meiyu events occurred in the El Niño or their following years, and 16 of total 21 mega-Meiyu events occurred with El Niño episodes. In the El Niño years, the meridional circulations were intensified over the mid-latitudes.The water vapor transported westerly and northerly to the mainland of China.A great amount of water vapor from south and the cold air from high latitudes intersected in the Mid-lower Reaches of the Yangtze River, which led to continuous precipitation. Moreover, in the El Niño following years, there was a steady subtropical high system at low latitudes. The transportation path of vapor was northerly, and then the vapor fluxes increased in Yangtze River Basin. The extreme Meiyu events occurred easier under this circulation background. [ABSTRACT FROM AUTHOR]