87th AMS Annual Meeting

Wednesday, 17 January 2007: 9:30 AM
Modeling of flash flood occurrence frequency in Southern California
213A (Henry B. Gonzalez Convention Center)
Theresa M. Carpenter, Hydrologic Research Center, San Diego, CA; and K. P. Georgakakos
Flooding and flash flooding are among the most devastating natural hazards, both within the U.S. and abroad. Globally, more than 6500 lives are lost each year on average in flooding disasters. Flash floods are defined as flooding events which occur shortly after antecedent precipitation event, typically within 6-12 hours. In the U.S., 80% of all flood related deaths in recent decades have been attributed to flash flooding. This presentation focuses on an effort to model and characterize the flash flood occurrence frequency and regional variability for Southern California. Southern California is selected for the case study because it possesses hydrologic and physiographic features often distinguished in flash flood prone areas: a significant atmospheric moisture source (the Pacific Ocean) and topographic features which augment precipitation and/or promote runoff concentration (the coastal mountain ranges). In addition, Southern California small scale flooding is driven by winter precipitation, which itself is sensitive to large scale climate forcing and climatic oscillations. Thus, the occurrence of flash flooding in the region is a manifestation of a rather unique coupling of hydrology, geomorphology and climate. This coupling forms the basis for regional-scale modeling of flash flood occurrence with high spatial resolution. This modeling combines dynamic downscaling of larger scale climatic forcing, distributed hydrologic modeling of soil moisture and surface runoff generation, and the hydro-geomorphologic response of small, flash-flood prone catchments. The model area is the cismontane region of the Southern California Bight, covering several thousands of square kilometers, with the resolution of the flash flood occurrence modeling being of the order of a few tens of square kilometers.

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