Characteristics of Record Floods from Landfalling Tropical Cyclones over the CONUS

Tropical cyclones (TCs) play a major role in characterizing the upper tail of extreme rainfall and flooding over the eastern US. In this study, we examine the record floods that are produced by landfalling TCs over the CONUS during the period of 1900-2017. Our analyses are based on annual flood peak observations from more than 5000 USGS stream gaging stations east of the Mississippi River together with the Atlantic hurricane database HURDAT2 for TC tracks and intensities. We present characterizations of record floods from landfalling TCs by introducing metrics that highlight the key physiographic (e.g., drainage area and slope) and hydrometeorological (e.g., rainfall intensity, distance to TC center, and relative location to TC tracks) ingredients that are associated with them. One important aspect of record floods is the spatial and temporal distribution of extreme rainfall. We examine the storm environment for record flood-producing TCs using the 20th Century Reanalysis fields as well as downscaling simulations using the Weather Research and Forecasting (WRF) model. Record floods induced by TCs concentrate along the eastern Coast and the Gulf of Mexico. There are a handful of record floods over the Great Plains that are tied to infrequent tracks of historical TCs, for instance, Hurricane Ike (2008). Spatial distributions of record floods highlight the roles of TC tracks, TC frequency as well as their interactions with mountainous terrains and midlatitude baroclinic features by extratropical transition. We provide detailed analyses for TCs that produced large numbers of record floods, for instance, Hurricane Agnes (1972), Hurricane Irene (2011), Hurricane Floyd (1999), and Hurricane Dianne (1955), each of them are directly responsible for more than 100 stations with record floods. Findings from our study can provide a predictive understanding of TC-related flood hazard, and serve as the basis for improved flood risk management under changing climate conditions.