摘要
20世纪长江流域曾出现上游洪水7次，中游洪水16次，下游洪水7次，其中有3次是全流域性洪水，分别发生在1998、1954和1931年。1998、1954和1931年梅雨期开始前（3～5月），长江流域降水比常年偏多。进入梅雨季以后，先后出现两场持续性暴雨：第1场出现在6月中旬至7月上旬，这场暴雨造成中下游河流的水位达到或超过警戒水位，出现局地洪涝；7月下旬长江中下游又出现1场持续性范围广的暴雨，雨水只能作为地面径流汇集到长江干流，造成很高水位的洪流。第2场持续性暴雨使长江上下游强降水时段在7月下旬重合，导致长江中下游干流洪水与来自上游的洪水在8月初至中旬遭遇，造成长江中下游灾难性的大洪水。1998、1954和1931年长江全流域性大洪水与东亚中高纬地区大气环流和东亚夏季风活动异常有联系。大气环流和东亚季风活动异常导致7月下旬西太平洋副热带高压的位置偏南，梅雨期持续到7月底，有利于长江中下游持续性暴雨发生的环流条件在7月下旬仍然存在。
The Yangtze River is the largest river in Asia and is vulnerable to flood disasters. During the 20th century, there are seven disastrous floods in the upper reaches, sixteen in the middle reaches, and seven in the lower reaches of the Yangtze River, in which three of them are basin-wide floods （1998, 1954 and 1931） . The hydrometerological conditions for these floods are given. Before the onset of the Meiyu season （March to May）, there was more precipitation in the middle and lower reaches of the Yangtze River valley, resulting in high water level in rivers and above normal soil moisture level. In the Meiyu period, there were two spells of persistent intense rainfall, one in the spell from mid June to early July, and the other in the late-half of July. After the first intense rainfall period, the water level of the streams and rivers in the middle and lower reaches exceeded the warning water level and lakes and floods were full. In late July when there occurred persistent intense rains, the water from the ensuring persistent heavy rains had no place to go other than into the streams and river courses, finally converging into the main stream of the Yangtze River and forming torrents with very high water levels. At the same time, the intense rain period in the upper reaches began and the high water level torrents from the upper reached the middle reaches in the early August. These torrents merged together, and resulted in extreme catastropic floods. Anomaly of atmospheric circulation and Asian summer monsoon results the Western Pacific subtropical high locating south of 30°N and available conditions for persistent heavy rainfall occurring in late-half of July.
出处
《气候与环境研究》
CSCD
北大核心
2006年第6期669-682,共14页
Climatic and Environmental Research
基金
国家重点基础研究发展规划项目2004CB418301
关键词
长江流域
洪水
暴雨
Yangtze River basin, floods, heavy rainfall
