Climatic background for historical flood of 1860, 1870 during past 500 years in the upper Yangtze River basin

Abstract

1860、1870年洪水是长江上游两次举世瞩目的出现于我国相对冷期的大洪水.它的出现似乎相悖于“以19世纪冷期与20世纪暖期相比,暖期大洪水出现频率高于冷期”的早期认识.通过对云、贵、川近500年历史气候研究,发现19世纪中后期至20世纪初,长江上游确为西南季风强盛的多雨期.1860,1870大洪水,尽管在百年尺度上,出现在我国小冰期第三个冷期,然而由于东西部差异,洪发当地在年代际尺度上,相对偏暖.因而长江上游于19世纪中叶前后,相对偏暖和强盛的西南气流与大洪水的孕育可能存在一定的联系.;I860, 1870 floods occurred during the relatively cold periods in the upper Yangtze River basin. This phenomenon is adverse to the idea that “greater occurrence possibility of floods happened to warmer periods after comparison between cold periods of 19th century and warmer periods of 20th century”. Researches on historical climatic changes during past 500 years in Yunnan, Guizhou and Sichuan, during middle and late 19th centmy and early 20th century, the upper Yangtze River basin is dominated by south-west monsoon. On the 100-year scale, 1860, 1870 floods occurred to the third cold periods during the Little Ice Age. As for the temporal and spatial distribution,the west parts of China is in relatively warm periods during the eastern ports of China is in cold periods (the relatively warm periods before the third cold periods).Relatively warmer and stronger south-west monsoon during around 19th century offered the good climatic background for these two flood events.