中文摘要：

利用国家气候中心的降水资料及NCEP／NCAR再分析资料、NOAA海温资料分析了华南地区5月降水的主要水汽通道及变异机制。发现异常多雨年的水汽主要来自南海、孟加拉湾和青藏高原南侧；异常少雨年则因西太平洋副热带高压（简称副高）偏东，来自南海的水汽缺失，只有来自孟加拉湾和高原南侧的两股水汽，因而南海的水汽是影响华南地区5月降水的重要因素。分析发现当北太平洋的准东西向海温异常是“负正负”分布时，南海地区为异常的反气旋性环流，有利于副高西伸加强；北太平洋海温距平为“正负正”异常分布时，南海地区为异常的气旋性环流，副高东退减弱。此外，北方南下冷空气的阻挡使得季风北界位置偏南，冷空气和季风在华南地区交汇导致5月降水异常增多。

英文摘要：

Precipitation data from the National Climate Center, China Meteorological Administrition, NCEP/NCAR reanalysis data, and Sea Surface Temperature （SST） data from NOAA are used to study the climatological characters of vapor transportation route and the differences in transport mechanism for the month of May in abnormally rainy and rainless years in South China. The results show that, in rainy years, moisture comes from the South China Sea （SCS）, the Bay of Bengal, and south of the Tibet Plateau. In rainless years the West Pacific Subtropical High （WPSH） is more eastern, and so vapor from the SCS, which is significant for the precipitation during May, cannot reach South China. When the SST anomalies in North Pacific have a quasi east-west ＂-＋-＂ pattern, anticyclones can be triggered in the SCS and WPSH can be enhanced and stretched westward. When the SST anomalies in North Pacific are ＂＋-＋＂, cyclones can be triggered in the SCS, causing eastward weakening of the WPSH. The front of the southwest monsoon will be further south because of the barrier of cold air, and the intersection of the monsoon and cold air in South China will cause more precipitation anomalies.