The corrected return period of a FEMA-defined 1-in-100-year flood using an updated version of NOAA precipitation statistics which accounts for an increase in heavy precipitation events in the past 20 years. This is an increasingly common type of flooding in urban areas that have been extensively paved over when climate change-boosted extreme rainfall events dump huge amounts of water on regions that drain poorly.įigure 1. FEMA maps do not factor in climate change and also do not account for the risk of “pluvial” floods. They are often out of date, available only as decades-old paper maps in some locations, and many local governments oppose efforts to update the maps for fear that it will depress property values and discourage development. Is the data good? FEMA maps have significant problems. If you are within a FEMA 1-in-100-year flood risk area, you could assume there is at least a 26% chance of a 1-in-100-year flood occurring over the span of 30 years. If you are in a FEMA 1-in-100-year flood risk area, you will be required to buy flood insurance from the National Flood Insurance Program in order to secure a federally backed mortgage. What it does: These maps show the expected 1-in-100-year and 1-in-500-year flood risk areas, which are regions that have a 1% per year and 0.2% per year chance of flooding, respectively. The back story: The traditional way to know your flood risk has been to consult the latest Federal Emergency Management Agency (FEMA) flood map through its Flood Map Service Center.
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