An Analysis on the Association between Flash Flood Occurrences and Average Recurrence Intervals of Rainfall and Streamflow

Radar-based rainfall and streamflow observations and forecasts are utilized to guide flash flood warning decisions in National Weather Service (NWS) operations. The recurrence intervals associated to these estimates can be used to establish the rarity of the hydrometeorological event and assess the likelihood of flash flood occurrence. To date, little work has been done to quantify the relation between the average recurrence interval of streamflow or rainfall to observed flooding events, how these relationships vary across the United States, or their uncertainties. In this work, we have explored the association of rainfall and streamflow recurrence intervals and the occurrence of flash floods across Continental United States. Flash flood occurrence is verified with U.S. Geological Survey (USGS) streamflow measurements and Local Storm Reports (LSRs) collected by NWS. The aim is to provide a robust quantification of average recurrence intervals of both streamflow and rainfall that are associated to observed flooding reports. This will extend the utilization of these products for real-time flood detection and forecasting in the NWS and beyond.