Causes Analysis of Severe Torrential Rain Inducing the Landslide in Shuicheng of Guizhou Province on 23 July 2019
Based on the precipitation data from China Meteorological Administration, ERA5 (the fifth generation of European Centre for Medium-Range Weather Forecasts Reanalysis) reanalysis data and the TBB (black-body temperature) data from FY-4A, the factors for the severe torrential rain causing landslide on 23 July 2019 were investigated. The results are as follows. The heaviest precipitation at 22:00 BT was caused by the convective cloud belt with TBB below -82℃. The synoptic systems were 750-700 hPa low trough and the cold front in the north of Sichuan Basin. Before the torrential rain, the cold front in the north of Sichuan Basin drove the air with large energy to flow from the basin to northwestern Guizhou. With the development of southern airflow in the south of Jichang Town, Shuicheng County of Guizhou Province, sufficient water vapor conditions were provided for the occurrence of the severe rainstorm. Meanwhile, the enhancement of warm and humid airflow made the convective instability in the lower layer of Jichang Town increase. At the beginning of the precipitation period (20:00 BT 22 July), the upward movement was mainly below 700 hPa, which was related to the influence of the easterly airflow that encountered the topographic obstruction and climbed along the slope of the terrain at Jichang Town. As the synoptic-scale cyclonic circulation extended into Guizhou Province, widespread precipitation occurred only in the narrow zones of the cyclonic circulation. After Barnes band-pass filter analysis, it is found that there were a number of small-scale cyclones and anticyclones in the synoptic-scale cyclonic flow field, and two small cyclone circulation on the west side of Jichang Town. The strong convergence zone on the north side of them was just the severe precipitation zone. At the same time, Jichang Town was also located in a small-scale saddle-shaped field region, which was obviously favorable for the convergence at low and middle levels, superimposed to the topographic upward motion. Therefore, the sudden severe torrential rain, resulting in the formation of landslides.