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100-Year flood–it's all about chance

April 17, 2010

In the 1960's, the United States government decided to use the 1-percent annual exceedance probability (AEP) flood as the basis for the National Flood Insurance Program. The 1-percent AEP flood was thought to be a fair balance between protecting the public and overly stringent regulation. Because the 1-percent AEP flood has a 1 in 100 chance of being equaled or exceeded in any 1 year, and it has an average recurrence interval of 100 years, it often is referred to as the '100-year flood'. The term '100-year flood' is part of the national lexicon, but is often a source of confusion by those not familiar with flood science and statistics. This poster is an attempt to explain the concept, probabilistic nature, and inherent uncertainties of the '100-year flood' to the layman.

Citation Information

Publication Year 2010
Title 100-Year flood–it's all about chance
DOI 10.3133/gip106
Authors Robert R. Holmes, Karen Dinicola
Publication Type Report
Publication Subtype USGS Numbered Series
Series Title General Information Product
Series Number 106
Index ID gip106
Record Source USGS Publications Warehouse
USGS Organization Office of Surface Water

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