Understanding flood risk in America

New flood modelling shows that 41 million Americans are at risk from flooding rivers, more than three times the current estimate.

The challenge

Existing regulatory flood maps produced by the Federal Emergency Management Agency (FEMA) cover about 60 percent of the continental US. These maps are produced by field teams of engineers visiting a catchment and collecting local data.

This method for assessing flood risk is the most precise approach, but the US is so vast that building a comprehensive national picture using this method is almost impossible. With limited time and resources, the FEMA flood maps focus on the most populated areas, leaving much of the country without any flood risk data.

What we’re doing

Working with teams across the Atlantic we have ‘redrawn’ the flood map of the US, filling in vast amounts of missing information.

We have produced a new high-resolution model that maps flood risk across the entire continental United States. As well as expanded coverage the map estimates flooding on small streams, something that wasn’t adequately captured in previous flood-risk models. This provides a much more comprehensive picture of flood hazard than has ever previously been made.

The study also integrates new maps from the Environmental Protection Agency that more precisely estimate where people live now and where future population growth is expected. Under these predictions, more than 60 million Americans may be vulnerable to a 100-year flood by 2050.

How it helps

The research will help fill a critical information gap for the many Americans that aren’t aware of the risk they face. People continue to build in harm’s way, often without realising they are doing so.

The study can provide the evidence base for comprehensive floodplain and flood risk management planning. Such planning will be critical as climate change may cause so-called 100-year floods to occur more frequently.

As well as risk to life, floods cause expensive damage to properly and infrastructure. Average flood losses have increased steadily to nearly $10 billion annually. The National Flood Insurance Program is no $24.6 billion in debt, not counting the projected $16 billion cost of hurricanes Harvey and Irma last year.

Lead researcher profile

Oliver Wing, PhD researcher looking at flood hazard modelling of the United States.

Partner organisations

  • FATHOM
  • US Environmental Protection Agency
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