Preparedness & Recovery

New Large-Scale Modeling Gives Worsening Picture of the Nation’s Flood Risk

More than 40 million people are at risk, and that number is expected to increase.

by Jim McKay / March 16, 2018

It’s well known that the current FEMA flood maps need updating, but some new information in a study done by researchers in the U.S. and England paints an even more ominous picture of the risk Americans face from flooding. 

The study estimated that slightly more than 40 million people in the continental U.S. are at risk for a 100-year flood event and that just 40 percent of the country is mapped. That 40 million is three times more than currently estimated and the amount of property in harm’s way is twice what the current risk is estimated to be. 

The study has been in the works for more than a year and involves using faster computers and new data from the EPA. The model looks at risk today and projects future risks based on where people will be moving and developing in the future. The researchers estimated that at the current rate, 60 percent of the population will be in a 100-year floodplain by the year 2050. And that doesn’t take into consideration any affects that a warming climate might have on future flooding. 

Kris Johnson, associate director for science and planning at the Nature Conservancy, and a co-author of the report, said that one of the main differences between this new model and smaller models typically used by FEMA, the Army Corps of Engineers and others is that the smaller models require people going out in boats to survey channels, bridges, depths of rivers, etc. The new, larger-scale modeling uses fewer data points and parameters to show risk over a larger area. 

“If you want to decide how to build a bridge over a particular river, you would want all those data points available,” Johnson said. “If you want information about how to plan floodplain on a large scale, then the modeling approach we’re using is quicker and cheaper and really accurate.”

He said the current modeling offers the ability to look over the entire U.S. and get a picture of who is at risk and where. The current, laborious, costly process of mapping has resulted in a patchwork of inaccurate maps scattered across the country. 

There have been recent improvements to mapping in some areas, but the progress has been slow and development in floodplains continues. 

“Despite the fact that we have the National Flood Insurance Program and land use regulations, we still see a lot of development happening in floodplains and a lot of development is projected to happen in floodplains,” Johnson said. 

Johnson called lidar (light detection and ranging) hugely beneficial in terms of getting a rich picture of what’s happening on the ground without having to go out on a boat, but said, “You still have to run a model to simulate how a flood wave is going to propagate itself down a river channel, and that’s where this large-scale modeling approach that we used comes into play.”

FEMA is aware of the modeling, and FEMA Deputy Public Affairs Director Eileen Lainez told the Miami Herald via email that models have to be certified before they can be used. “We welcome new models in science, and as the models described in the article mature, we would look forward to reviewing and including the best of this science into our program,” she said.