The Relationship between Extreme Precipitation and Damaging Floods in the Northeastern United States

The northeastern United States has experienced an increase in extreme precipitation over the last three decades, which has substantial implications for flooding. However, the relationship between extreme precipitation and societally relevant flooding in the Northeast is not well understood. Here, we investigate the association between precipitation, antecedent wetness, and damage-producing warm-season (June-November) flood reports in the Northeast, 1996-2020. We employ 4-km gridded daily precipitation data aggregated to the county scale to calculate 1- and 3-day precipitation and a standardized precipitation index at multiple time scales. From these, we determine extreme precipitation and extreme antecedent wetness thresholds to identify hydroclimatic extreme events and relate them to damaging flood occurrences from the NOAA Storm Events Database. We fi nd that damaging floods frequently occur with relatively high precipitation and antecedent wetness, although there are exceptions in several counties. However, the majority (54%) of damaging floods are not associated with extreme precipitation or extreme antecedent wetness, and more than 90% of hydroclimatic extreme events are not associated with floods. We explore limitations to the definitions of extreme precipitation and extreme antecedent wetness by varying the threshold. Lower hydroclimatic extreme event thresholds not only have a greater likelihood of being associated with damaging floods but also have a greater number of hydroclimatic extreme events not associated with a damaging flood; the opposite holds for higher thresholds. We address these challenges by combining precipitation and antecedent wetness to identify coordinated thresholds that best capture damaging flooding in each county.