西南地区夏季极端降水的水汽来源分析

西南地区地形复杂,极端降水极易形成山洪并引发地质灾害,1998年夏季西南降水达709.3 mm,超出平均降水约23.9%。经使用水汽追踪模型WAM2layers和ERA-Interim再分析资料等大数据追踪西南降水水汽来源,发现西南夏季降水主要有四个源区,分别是西南季风区、西风带区、本地和东南季风区,1998年夏季分别贡献了330.1 mm、110.0 mm、104.8 mm和65.6 mm水汽,约占所追踪降水的52.2%、17.4%、16.6%和10.4%。西南季风区作为最大源区,贡献了超过一半的降水水汽。增加的降水其水汽主要来自西南季风区、西风带区和本地,比平均分别多贡献80.1 mm、29.3 mm和27.1 mm,合占所增加降水的99.9%;其中又以西南季风区贡献占主导。进一步发现,1998年夏季太平洋副高向西南延伸,并在北孟加拉湾和我国南海形成两个高压中心异常,导致西南季风向我国西南地区的水汽输送异常强劲,从而造成西南地区降水异常增多。

An analysis on moisture source of extreme precipitation in Southwest China in summer

The terrain in Southwest China (SWC) is very complicated, and it is prone to floods and relative geological disasters due to heavy rain. In summer 1998, the SWC precipitation reached a maximum of 709.3 mm, which is around 23.9% above the climate mean. By using a Eulerian model of moisture recycling WAM2layers and big data such as ERA-Interim reanalysis, the precipitation moisture in summer SWC was backtracked. It is found that there are four major source regions for SWC, which are the southwest monsoon region, the westerlies region, the local region, and the southeast monsoon region. They contributed around 330.1 mm, 110.0 mm, 104.8 mm, and 65.6 mm in water depth of SWC in summer 1998, which accounted for 52.2%, 17.4%, 16.6%, and 10.4% of the tracked precipitation moisture, respectively. The southwest monsoon region, from the west Indochina Peninsula to the Indian subcontinent to the Indian Ocean, as the largest moisture source, contributed more than half the precipitation moisture. The extra moisture of the extreme precipitation during summer 1998 came mainly from the southwest monsoon region, the westerlies region, and the local region, contributing about 80.1 mm, 29.3 mm, and 27.1 mm, respectively, above the average moisture contribution, which together accounted for 99.9% of the extra precipitation. The southwest monsoon region dominated the extra moisture contribution once again. Further analyses revealed that the Western Pacific subtropical high (WPSH) stretched to the southwest, forming two anomalous highs in the Northern Bay of Bengal and the South China Sea. This change made moisture transport by the southwest monsoon to SWC extremely strong, which resulted in extreme precipitation in SWC.