Environment

Beyond FEMA: New flood maps show more areas at risk in North Carolina

High flood risks in Boone: Orange dots represent areas prone to major flooding; dark red dots represent an extreme flooding risk. (Map: Flood Factor/First Foundation)

New flood maps that account for intense rainfall and climate change show what many residents of western North Carolina already know: The mountains can be every bit as treacherous as the coast for flooding.

Flood Factor, a new interactive mapping tool, was developed by the First Street Foundation, a nonprofit that taps into the expertise of leading academic researchers, GIS analysts, programmers and data visualization specialists.

It analyzed 142 million properties nationwide  and their elevations, and historic and future rainfall estimates, to indicate any location’s risks of flooding from intense rainfall, rivers, tides and storm surge. First Foundation also modeled for climate change to show how the flood risks will change by mid-century. The methods were reviewed by an academic panel and submitted to peer-review journals, according to the foundation.

The New York Times has an interactive map based on Flood Factor’s data; the Flood Factor website allows you to enter a ZIP code, property address, city or state to learn the flood risk.

These are the 21 counties where FEMA maps significantly underestimate the flooding risk:

CountyFlood Factor % of properties at risk from a major stormFEMA % of properties at risk
Cherokee18.22.5
Graham31.36.2
Alleghany12.21.1
Ashe24.24.6
Watauga182.7
Avery19.23
Mitchell23.31.7
Yancey27.23.6
Madison27.23.3
McDowell14.12.2
Buncombe13.42.1
Haywood23.66.3
Transylvania15.13.4
Jackson19.43
Swain25.55.3
Macon16.9
2.6
Clay17.4
5.1
New Hanover24.413.2
Perquimans31.420.8
Currituck35.717.4

In some areas of eastern and coastal North Carolina — Hyde, Dare, Lenoir and Beaufort counties, for example, Flood Factor actually shows a lower chance of flooding than the FEMA maps. The New York Times quoted First Street as saying that “in some areas … the model may overestimate flood risk because it doesn’t capture every local flood-protection measure, such as pumps or catchment basins.”

All of inland central North Carolina, from the Foothills to the Coastal Plain, is also more susceptible to flooding, up to 10% higher risk than the FEMA maps show.

FEMA maps can be outdated or incomplete; they are also heavily politicized because a property’s location in or near a flood-prone zone can increase insurance rates or preclude developing the area altogether.

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