Increasing frequency of intense rainfall events and flood damage in the northeast U.S. suggest a corresponding increased need for improved flash flood warning systems. Current National Weather Service operational practice involves overlaying of gridded antecedent rainfall data with real-time Doppler radar to determine where warnings are to be issued. This approach does not consider spatially varying susceptibility of the landscape to flash flooding. We investigate stream flashiness as a function of urbanization and various watershed characteristics, focusing on the Delaware River region where heavy precipitation and large flood events have increased in recent decades. The dataset includes streams with a continuous flow record from 2010 to present, limited reservoir storage and flow regulation, and drainage area less than 250 sq km. We show that flood susceptibility as measured by a flashiness index and peaks-over-threshold frequency is a complicated function of watershed characteristics, including urban land use, wetlands, slope, soils, and drainage area. Although urbanization is a dominant factor, it is not the case that urban or suburban watersheds are invariably flashier than rural watersheds in our study area of varying land use and physiography. Further work will focus on developing a multivariate model of flash-flood susceptibility that can inform current operational practice.

Flash Flood Susceptibility in the Delaware River Region

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[Paper Proceedings](https://doi.org/10.1061/9780784483466)

Conference DOI: https://doi.org/10.26226/m.6329c39b68fb0e00131f77d2