Introducing Flashiness‐Intensity‐Duration‐Frequency (F‐IDF): A New Metric to Quantify Flash Flood Intensity.

Flash flooding is a damaging weather event, yet it remains challenging to quantify its severity. We propose a development—the Flashiness‐Intensity‐Duration‐Frequency (F‐IDF) curve—to quantify flash flood intensity based on the frequency and duration of the event. As a proof‐of‐concept, we mapped Contiguous US (CONUS)‐wide F‐IDF values at 3,722 stream gage locations and explored their relations with basin attributes. It is found that (a) The return periods of flash flood events are highly associated with the return peroids of rainfall events; (b) Climatological precipitation amounts exhibit the most positive correlation with flashiness while a basin's drainage area is the most negatively correlated; (c) Correlation of flashiness with basin attributes decreases with increasing F‐IDF return periods and shorter event durations. Both aspects are attributable to the rainfall signal overwhelming the underlying basin attributes as the intensities become more extreme. This new metric has implications for hydrology and emergency responders. Plain Language Summary: Flash floods are among the most devasting natural hazard types that can cause severe property damage and loss of life. However, it's challenging to measure and quantify the severity. This study proposes a new way of quantifying flash flood intensity using a newly developed Flashiness‐Intensity‐Duration‐Frequency (F‐IDF) curve. It links flash flood severity with how often they happen and how long they last. We mapped F‐IDF values across the United States and found that certain areas are more prone to flash floods than others. The amount of rain and the size of the basin area are the most important factors in determining how severe a flash flood is. This new quantification tool can help experts better identify and respond to flash flood risks. Key Points: We introduce the Flashiness‐Intensity‐Duration‐Frequency curve to quantify flash flood intensityThe CONUS‐wide Flashiness‐Intensity‐Duration‐Frequency values are provided at 3,722 stream gage locationsThe relations between 59 basin attributes and flashiness values are explored [ABSTRACT FROM AUTHOR]