Assessing pluvial flash flood hazard in southeast US (SEUS)

According to the National Weather Service (NWS), a flooding event which is initiated within six hours is referred to as flash flood. Pluvial flash floods are common in southeastern US as a result of frequent extensive heavy rainfall caused by tropical storms, thunderstorms, and hurricanes. During the past decades, flash floods imposed billions of dollars damages to southeast US (SEUS). In this study, flash flood characteristics such as frequency, duration, and intensity are analyzed to assess flash flood hazard at a county level across nine southeastern states of the US (i.e. Alabama, Arkansas, Florida, Georgia, Louisiana, Mississippi, North Carolina, South Carolina, and Tennessee). The National Oceanic and Atmospheric Administration (NOAA) storm events database is utilized to study the duration and frequency of flash floods for 755 counties during 1996 to 2017 (the entire period of data availability). Then, hourly precipitation data is acquired from Phase 2 of the North American Land Data Assimilation System (NLDAS-2) and the spatiotemporal patterns of flash flood intensity are also determined. Flash flood hazard is then assessed by integrating the three primary attributes (i.e. frequency, duration, and intensity), and seasonal and spatial characteristics are identified. Results show that flash floods happen more often in spring and summer, and in general, western parts of SEUS receive prolonged and more frequent flash floods compared to the eastern regions. A spatial coherence is detected between duration of flash floods and monetized property damages. The result of this study improve the understanding of flash flood hazard across the SEUS and they can be useful for flash flood risk management and disaster mitigation.