Climate data used to assess flood risk

Report says dangers were underestimated

A study released Monday showing that federal authorities have underestimated the flood risk for millions of properties across the U. S. was three years in the making.

The report by First Street Foundation drew on decades of peer- reviewed research and the expertise of more than 70 scientists, technologists and other experts to calculate the current and future flood risk for each property in the lower 48 states and D. C.

First Street’s scientific model shows 14.6 million properties – 10.3% of all properties in the 48 states – are at risk from a 1- in- 100- year flood, compared with 8.7 million properties under the Federal Emergency Management Agency’s current flood maps.

The largest donors to the analytical effort were the High Tide Foundation, which says its goal is to support climate change mitigation efforts, and the 2040 Foundation, which says it aims to address the cost of climate change on the nation’s energy infrastructure.

First Street has been developing its model since the nonprofit opened in 2017.

The project is the first of its kind in scope and accessibility. The group is giving the public free access to the property- specific data through a web application called Flood Factor.

The research radically alters the picture provided by FEMA. The agency is tasked with making maps of areas exposed to different levels of flooding. But many of the agency’s maps are outdated, and FEMA hasn’t measured the risks for large swaths of the U. S.

First Street created one national model to look at all the flood risks for a

A key difference from FEMA is First Street incorporates historical climate and insurance data.

property, whether it comes from high tides, rainfall, rivers or hurricane storm surge. Future risk calculations are based on the set of scenarios used by the Intergovernmental Panel on Climate Change.

Past efforts have focused on separate models for each risk.

“The thing that we did that’s unique is we not only pulled that together and created this model at the property level that hadn’t been done before, then we also adjusted it into the future,” said Matthew Eby, First Street’s founder and executive director.

A key difference from FEMA’s approach is that First Street incorporates historical climate and insurance claim information, as well as future climate projections from the climate change panel. FEMA develops regulatory flood maps based on historical data alone.

First Street also included floodmitigating infrastructure in its model, such as levees, beach nourishment projects and wetland restoration projects.

The estimates of numbers of properties at risk under First Street’s model versus FEMA’s maps differ dramatically in many areas of the country, with FEMA underestimating risk in the majority of the U. S. and overestimating it in some pockets.

For example, in Cook County, Illinois, which encompasses the city of Chicago, about 25,000 properties fall within FEMA’s flood risk area. First Street’s model shows roughly 150,000 properties – 11% of properties in the county – are at risk. By 2050, an additional 11,000 properties will be at risk.

In some Gulf communities, First Street’s estimates are in line with or lower than FEMA. In Port Arthur, Texas, the group estimates 15% of properties are at risk, compared with 17% under FEMA’s maps. But by 2050, First Street estimates as many as 96% of properties will be at risk for flooding.

The foundation’s methodology is still undergoing peer review. Three independent experts reviewed and approved of the model before its release.