Spatial-Temporal Distribution and General Circulation of Rainstorm over the Upper Reaches of Dadu River in 2009-2019

Based on rainfall data and the NCAR/NCEP 1°×1° reanalysis data over the upper reaches of Dadu River from 2009 to 2019,composite analyses of rainstorm over the Upper Reaches of Dadu River was carried out.The results show that:There were 28 cases of rainstorm over the upper reaches of Dadu River from 2009 to 2019,and most times in 2014.The occurrence seasons were mainly in June to September,with the most in June,accounting for 28.6% of the total times.The heavy rainfall concentrated from 20:00 p.m. to 2:00 a.m.,with obvious diurnal variation.The frequency of rainstorm was more in the middle and less in the north and south,and the center was located in Barkam.Based on the different influencing system of the rainstorms,they could be divided into three types,which were high trough type,plateau shear line type and plateau vortex type,accounting for 46.4%,35.7% and 17.9% respectively.The high trough type was the most in September,the plateau shear line was the most in July,and the plateau vortex type was the most in June.The circulation characteristics of different types of rainstorm were analyzed for three historical cases.