Planning & Management

Oral

395286 - Informing policy choices with regional estimates of flood risk across the United States

Tuesday, June 5
4:00 PM - 5:30 PM
Location: Greenway GH
Co-Authors: Jerry Stedge, Maryland – Abt Associates; Brad Firlie, Maryland – Abt Associates; Pearl Zheng, Maryland – Abt Associates

Floods are known to be the most damaging natural disasters in the U.S. The Federal Government plays a large role in reducing flood risk and recovering from floods, spending billions of dollars each year on programs to reduce flood risk, including building and maintaining flood control infrastructure, mapping areas prone to flood, subsidizing flood insurance, and providing grants to localities to implement local risk management projects. Further, in recent years large flood disasters have resulted in repeated emergency expenditures. With growing fiscal pressures at the Federal level and on-going discussions about the role of the Federal in flood management, there is a need to better understand how flood risk and resilience vary across the United States. This paper reports on an effort to develop a national flood risk characterization using data from the Federal Emergency Management Agency (FEMA), the U.S. Census, U.S. Geological Survey (USGS), the U.S. Army Corps of Engineers (USACE), and other sources. The analysis relies on mapping of the 1% annual chance exceedance flood as a proxy for overall hazard and risk. FEMA’s National Flood Hazard Layer, which includes geospatial data on all mapped 1% ACE floods, is used with USGS National Elevation Dataset to estimate a distribution of flood depths across all floodzones in the U.S. Mapped floodzones are then overlaid with Census blocks to estimate population and building exposure. Exposure is assumed to be proportional to areal overlap of Census blocks and floodzones, with population derived from Census data and building inventory coming from FEMA’s HAZUS. Finally, damages are estimated for exposed buildings using standard depth-damage functions from FEMA and USACE. Exposure and damage estimates are summed to counties and HUC-8 watersheds for comparing risk across different areas of the U.S. Results are compared to more detailed local and regional studies for validation.

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