Watershed

Oral

395134 - Assessing the Regional Frequency, Intensity, and Spatial Extent of Tropical Cyclone Rainfall

Wednesday, June 6
8:30 AM - 10:00 AM
Location: Greenway IJ
Co-Authors: Daniel Wright, Madison, WI – University of Wisconsin - Madison; Phu Nguyen, Irvine, CA – University of California – Irvine

While the strength of a hurricane is generally classified based on its wind speed, the unprecedented rainfall-driven flooding experienced in southeastern Texas during Hurricane Harvey clearly highlights the need for better understanding of the hazards associated with extreme rainfall from hurricanes and other tropical systems. In this study, we seek to develop a framework for describing the joint probabilistic and spatio-temporal properties of extreme rainfall from hurricanes and other tropical systems. Furthermore, we argue that commonly-used terminology – such as the “500-year storm” – fail to convey the true properties of tropical cyclone rainfall occurrences in the United States.

To quantify the magnitude and spatial extent of these storms, a database consisting of hundreds of unique rainfall volumetric shapes (or “voxels”) was created. Each voxel is a four-dimensional object, created by connecting, in both space and time, gridded rainfall observations from the daily, gauge-based NOAA CPC-Unified precipitation dataset. Individual voxels were then associated with concurrent tropical cyclone tracks from NOAA’s HURDAT-2 archive, to create distinct representations of the rainfall associated with every tropical system making landfall in (or passing near) the eastern United States since 1948.

Using these voxels, a series of threshold-excess extreme value models were created to estimate the recurrence intervals of extreme tropical cyclone rainfall, both nationally and locally, for single and multi-day timescales. This voxel database also allows for the “indexing” of past events, placing recent extremes – such as the 50+ inches of rain observed during Hurricane Harvey – into a national context and emphasizing how rainfall totals that are rare at the point scale may be more frequent from a regional perspective.

Christopher D. Bosma

Research Assistant
University of Wisconsin - Madison

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395134 - Assessing the Regional Frequency, Intensity, and Spatial Extent of Tropical Cyclone Rainfall



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