The spatial and temporal distributions of warm sector rainfall and frontal rainfall for the torrential rain event in Beijing on 21 July 2012

Using the conventional observation data, the data from intensive automatic weather stations, FY-2E infrared images, Doppler weather radar products and NCEP/NCAR 6-hourly reanalysis data, we have conducted detailed analysis and division to warm sector rainfall and frontal rainfall for the torrential rain event in Beijing on 21 July 2012, and carried out comparative analysis of the spatial and temporal distribution of the different stages of rainfall during the event. The results indicate that the entire torrential rain event can be divided into three stages based on the movement of cold front passing through the center of the total precipitation. The first stage is from 08:00 BT to 16:00 BT on 21 July 2012 and characterized by prior-frontal warm sector rainfall, in which the maximum precipitation center is located in the Juma River basin in Hebei province and the second large one in the southwest part of Beijing. The second stage is from 16:00 BT to 20:00 BT on 21 July 2012 and characterized by frontal rainfall when the front moves across Beijing, with the maximum precipitation center being in Fangshan district in the southwest part of Beijing. The last stage is from 20:00 BT 21 July to 03:00 BT 22 July 2012, in which post-frontal precipitation is obvious in the southwest part of Beijing, with the maximum precipitation center being located in the junction of the southeast part of Beijing and Hebei province and corresponding to the cold front position. The precipitation in the torrential rain center for the whole event includes the warm sector rainfall, the frontal passage rainfall and the post-frontal rainfall, which account for about 40%, 46% and 14% of total rainfall, respectively. Precipitation in the northwestern, northeastern and southeastern parts of Beijing is mainly composed of frontal rainfall, of which the proportion of warm-vector rainfall is less than 15%. The floods in the Juma River basin of Hebei province are mainly caused by warm sector rainstorm, while those in the southwest part of Beijing are contributed to by both the warm sector rainstorm and the frontal passage rainstorm.