Feds Underestimating Flood Risk and ‘The Strangeness Index’  

Posted by Bill Raymor on Mar 14, 2018 8:00:00 AM

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PropertyCasualty360 published an article in December, 2017 that begins with this eye-opening quote, “Research conducted by a team of U.S. and U.K. scientists and engineers suggests that U.S. federal flood maps underestimate the number of Americans at risk for flood by more than 27 million people.”

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A study from IOPscience gave a more onerous estimate of 41 million Americans living on the 100 year floodplain. And, with a value of $5.5 trillion! In contrast, current FEMA estimates are around 13 million Americans.

At the 2017 American Geophysical Union Meeting Dec. 11-15 in New Orleans, scientists presented a ‘redrawn’ flood map of the U.S. (coastal areas excluded) simulating every river catchment area. Intermap’s InsitePro flood mapping tool uses a mathematical tree structure called the Strahler Number to predict risk. It is a numbering system that correlates a numeric value to stream size from small tributaries to large riverways. The entire algorithm then uses our proprietary 5m seamless & contiguous bare earth elevation dataset to generate location specific flood risk scores.

Even the Department of Homeland Security and the Office of the Inspector General in a September, 2017 report titled FEMA Needs to Improve Management of Its Flood Mapping Programs had this to say: “Without accurate floodplain identification and mapping processes, management, and oversight, FEMA cannot provide members of the public with a reliable rendering of their true flood vulnerability or ensure that NFIP rates reflect the real risk of flooding.”

Added to all this is a joint modeling project by hydrologists in a Princeton-Bristol University partnership where they have developed a ‘Strangeness Index’. Here is a quote from the BBC article

  • “These researchers developed what they termed a "strangeness index" for flooding. That is worked out by dividing the volume of water recorded in the largest flood, by the volume from a more typical flooding event. "The higher that value on the strangeness index, the more likely the flood is to happen at an unexpected time of year," explained Alexander Cox from Princeton University.”

All of these notations point to a greater need for Title II of the 21st Century Flood Reform Act (again from PC360): Increasing consumer choice through private market development.

Flood Risk Score is a solution

Topics: FEMA, Risk Scoring, Flood Risk, Flood Insurance, Floods

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