Study on the waterlogging threshold of heavy precipitation in the densely populated areas of Shanghai

Based on hourly waterlogging disasters and hourly rain data from weather stations in dozens of obvious heavy rain events in Shanghai during 2012-2015, the temporal and spatial dynamic evolution relationships between precipitation and the number of waterlogging disasters were analyzed, and waterlogging threshold indicators were established in densely populated areas of Shanghai.Results indicate that the waterlogging threshold is 30 mm per hour in urban district of Shanghai.Waterlogging disasters will increase significantly when the rain intensity reaches 70 mm per hour or more.The waterlogging threshold is 35 mm per hour in other counties of Shanghai.The severity of waterlogging is not only related to the rain intensity, but also associated with the cumulated precipitation and the precipitation duration.When accumulated precipitation reached more than 40 mm in two hours, waterlogging disaster will occur.Waterlogging disaser has a lag of about 1-2 hours relative to the occurrence of heavy precipitation.