一次致洪大暴雨对长江两个子流域的影响分析

On Impact of a Flash Flood-Inducing Rainstorm upon Two Sub-Basins of Yangtze River

利用高空、地面观测和NCEP/NCAR再分析资料,对2009年8月3日-5日发生在长江两个子流域(嘉陵江和綦江流域)的一次致洪大暴雨的降水时空分布、环流背景、水汽输送及对流域水文条件的影响进行了分析.结果表明:此次暴雨环流背景是高空槽耦合了"天鹅"台风阻塞的西南低涡,南侵冷空气和西南急流输送的暖湿水汽交汇,导致不断有中小尺度对流系统的生成、发展;暴雨第一阶段降水是纬向和经向水汽输送的共同作用,第二阶段以纬向输送为主;两个子流域暴雨期间700hPa比湿值一直在10g/kg以上,最强降水均产生在水汽通量大值区,同时也是水汽通量散度梯度最大处,产生时间则为低层散度值变化最大梯度期间;綦江流域降水比嘉陵江流域降水持续时间短,但其流域面积小,面雨量反而更大,造成其先达到最高水位,超保证水位,嘉陵江未超警戒水位,本次致洪暴雨造成两流域及长江上游均达到一年中最高水位.

Based on the data of routine sounding,surface observation,satellite and radar,as well as reanal-ysis data from NCEP/NCAR,the precipitation on spatial and temporal distribution,circulation back-ground,water vapor and the impact on the hydrological conditions of a flash flood-inducing rainstorm have been analyzed.The flood took place in 2 sub-basin of the Yangtze River (Jialing River and Qi River),on 3 to 5 August 2009.It has been found that the storm circulation background is upper trough coupled south-west vortex of the“Swan”typhoon blocking,and the southward invasion of cold air and warm water vapor the intersection of the southwest j et transport,resulting in continuous generation and development of me-soscale convective systems.The first stage of precipitation is the combined effect of the zonal and meridio-nal water vapor transport,and the second stage is mainly due to zonal transportation.During heavy rain-storms the specific humidity at 700 hPa is more than 10 g/kg in both sub-basins,and the strongest precipi-tation are generated in the water vapor flux divergence maximum gradient.The time of precipitation is shorter,the quantity of precipitation is less,but the basin area is smaller in Qi River sub-basins than Jial-ing River sub-basins,So areal precipitation is more in Qi River sub-basins,which resulted in the flood e-vent had a water level higher than safety stage in Qi River sub-basin and only higher than warning stage in Jialing River.The highest flood peak measured at the Cuntan station of the Yangtze River in 2008 is com-bined effect by the two sub-basins’annual highest flood peak.