1849年长江中下游大水灾的时空分布及天气气候特征

Spatial and temporal distribution and climatic characteristics of flood in middle and lower reaches of the Yangtze River in 1849

清道光二十九年(1849年)长江中下游地区的大水灾,对民生造成了严重的影响。作者系统收集了档案、方志、日记和文集资料中关于该年份水灾的记载,以县级成灾分数资料为基础,重建了此次水灾的时空分布,并分析了形成这次水灾的天气气候特征。研究认为,该年度水灾基本在N28°～N33°间呈条状东西向分布,而以N31°一线的灾情最为严重;连续性的降水开始于5月18日左右,到7月18日才结束,中间还有3次持续各达10余天的强降雨过程;这次大水灾是全流域性的,涝灾大于洪灾,降水最集中区域为东部的太湖流域,这和有器测记录的几次长江全流域大洪水并不一致;本次大水灾的直接天气成因是梅雨期提前并超长,雨量明显偏大,持续时间长达62天左右,比有器测记录的更早、更长;当年夏季风应偏弱,副热带高压脊线位置异常偏南,且西风分支明显,经向环流发展,西风南支位置应该也异常偏南;夏季冷空气异常活跃可能是雨带长期在长江沿岸徘徊的真正原因。

This article focused on the serious flood in the middle and lower reaches of the Yangtze River in the year 1849. The author consulted a variety of resources about this flood, such as archives, local gazetteers, diaries and other personal literatures, and based on the county-level index and details of disaster, spatial and temporal distribution of the serious flood disaster is reconstructed. It was shown that a west-to-east zonal distribution of the disaster was between N28°and N33°, with the extremely serious band along N31 °. Continuous rainfall was from May 18th to July 18th, with three heavy rains events each lasting more than 10 days during this process. This article pointed out that, this particular disaster covering the whole Yangtze drainage was behaved as a waterlog rather than a flood. The flood is very different from other instrument-recorded all-over-basin flood that the rainfall was concentrated in the Tai Lake basin in eastern part of the Yangtze River. The main cause of these features in this disaster was the occupation of the plum rain season which had lasted 62 days and the precipitation obviously increased. It should be also considered that the summer monsoon was weaker in that year, and the Subtropical High Ridge Line was unusually bended southwards. Furthermore, the branch of westerly wind played a strong role together with the development of the Meridional circulation, so that it could be deduced that the branch of westerly wind was abnormally located southwards. Besides, the irregular activities of cold air in summer were probably the real factor which drove the rain band staying along the riverside of the Yangtze River for such a long period of time.