Evolution characteristics of sudden mountain rainstorm events in Sichuan Province from 2008 to 2017

The secondary disasters such as flash floods, landslides and debris flows induced by sudden mountain rainstorm are major natural disasters in mountain areas of China. In this paper, the statistical characteristics of sudden mountain rainstorm events in Sichuan Province are analyzed by using the 10 year hourly precipitation data of national stations from 2008 to 2017. The results are as following: (1) During the 10 years from 2008 to 2017, there were 979 sudden mountain rainstorm events in Sichuan Province, with an average of 98 events per year. More than 5 sudden rainstorm events occurred in most areas. Sudden rainstorm events mainly occur in the Sichuan Basin and its eastern and southern mountainous areas, and the frequency of sudden rainstorm events in the western mountainous areas is far higher than that in the eastern mountainous areas, which indicates that it is closely related to the terrain. (2) The sudden rainstorm events increased from April, increased by leaps and bounds from June to July, and gradually decreased after July. The sudden rainstorm events at night is more than that in the daytime. The high-frequency distribution of sudden rainstorm events starts at 16:00 pm. in the western mountainous area of Sichuan Province, and turns to the highest in the eastern mountainous area at midnight, which shows that there is a process of development and propagation of heavy rainfall from west to east. (3) The duration of mountain sudden rainstorm events is mostly concentrated in 3~12h, and the average duration is longer in June, July and September, but shorter in May and August. (4) The annual average rainfall of sudden mountain rainstorm events ranges from 80 mm to 120 mm. The accumulated rainfall is the largest in July, followed by August, and the smallest in May and September. In 2015, the frequency of sudden mountain rainstorm events was the least, but the annual average accumulated rainfall was the most, indicating that the intensity of sudden rainstorm was the largest in 2015.