Abstract: Based on the precipitation observation data from 1937 to 2018 of the Xifeng National Basic Weather Station in Qingyang city and the waterlogging data recorded in the Qingyang city, the annual precipitation concentration and concentration period, as well as the formula of the intensity of torrential rain were calculated by counting the strong precipitation frequency and the 95%, 99% fractional values total precipitation. Combined with urban drainage network simulated using SWMM system, we aim to analyze and evaluate the risk of waterlogging in the city of Qingyang, and determine the threshold of urban precipitation in Qingyang city as a standard for the release of urban monitoring and warning information. The results show that extreme precipitation is the main cause of urban waterlogging in Qingyang city,which generally concentrates in summer, mostly in July to August. Two factors have positive relationships with extreme precipitation： Total precipitation and intensity. The greater the total precipitation and the heavier the intensity,the more serious of the urban waterlogging disaster. When the total precipitation reaches more than 30 mm,precipitation intensity becomes particularly important：when the precipitation reaches 15 mm in 30 minutes, waterlogging points are prone to water accumulation;When the precipitation reaches 20 mm in 30 minutes, the waterlogging point may have disasters;When the precipitation reaches 30 mm in 30 minutes, the waterlogging point is prone to serious disasters;When the precipitation reaches 40 mm in 30 minutes, the waterlogging point disaster will be very serious. By using SWMM system simulation, we found that waterlogging disaster is not only related to extreme precipitation and regional distribution, topography, pipe network and runoff are also important factors leading to urban waterlogging.

Key words: urban waterlogging, extreme precipitation, torrential rain intensity formula, SWMM simulation, Qingyang city