Abstract:

Based on the daily precipitation data of 156 weather stations in Sichuan Province and NCEP/NCAR reanalysis data, the temporal and spatial distribution characteristics of extreme precipitation events in midsummer in Sichuan Province and their relationship with Tibetan Plateau summer monsoon were analyzed during 1961-2015. The results show that the climate tendency rate of extreme precipitation indexes in midsummer in Sichuan had an obvious spatial difference during 1961-2015, PPER decreased in most areas of Sichuan, while PRCPTOT, R95p, SDII, RX1day and RX5day mainly appeared a decreasing trend in western Sichuan basin and the northwestern part of the plateau of western sichuan and an increasing trend in other regions in recent 55 years. From the whole area of Sichuan Province, the decreasing trend and mutation of PRCPTOT in midsummer were not obvious during 1961-2015, while the decreasing trend of PPER was significant with an obvious mutation in 1985. SDII and R95p in midsummer increased significantly on the whole and happened obvious mutation in 1980 and 1990, respectively, while RX1day and Rx5day increased non-significantly and happened three obvious mutations. The extreme precipitation indexes in midsummer in Sichuan had 3 to 4 years and 8 years periods oscillation from 1961 to 2015. The extreme precipitation in midsummer in the east and west of Sichuan basin was closely related with the anomaly of Tibetan Plateau summer monsoon. When the Tibetan Plateau summer monsoon was strong, the meridional circulation was dominant over the middle and high latitude areas of East Asia on composited 500 hPa geopotential height anomaly field. At the same time, the western Pacific subtropical high was southward, and the southwesterly wind and water vapor from the Bay of Bengal strengthened, which was beneficial to more (less) extreme precipitation in the east (west) part of Sichuan basin in midsummer. However, when the Tibetan Plateau summer monsoon was weak, the situation was the opposite.

Key words: extreme precipitation, temporal and spatial characteristics, periodic characteristics, Tibetan Plateau summer monsoon

摘要：

利用1961—2015年四川省156个台站逐日降水资料和NCEP/NCAR再分析资料，分析了四川省盛夏极端降水事件的时空分布特征及其与高原夏季风的关系。结果表明：近55 a四川省盛夏极端降水指数的变化趋势具有明显的区域差异，降水百分率在四川大部分地区呈减少趋势，而降水总量、强降水量、降水强度及1日、连续5 d最大降水量主要在川西高原西北部和盆地西部呈减少趋势，其他区域则呈增加趋势。就全省而言，近55 a四川盛夏降水总量整体呈不显著减少趋势，未发生明显突变，而降水百分率呈显著减少趋势，且发生了1次显著突变；降水强度、强降水量整体呈显著增加趋势，且发生了1次显著突变，而1日、连续5 d最大降水量呈不显著增加趋势，且发生了3次显著突变。四川盛夏各极端降水指数均存在3~4 a和8 a左右的振荡周期。四川盆地东、西部盛夏极端降水与高原夏季风异常关系密切，高原夏季风偏强时，500 hPa高度距平合成场上东亚中高纬地区以经向型环流为主，西太平洋副热带高压偏南，来自孟加拉湾的西南风水汽加强，有利于四川盆地东（西）部盛夏极端降水偏多（少）；高原夏季风偏弱时，情况则相反。

关键词: 极端降水, 时空特征, 周期特征, 高原夏季风