A standard part of due diligence before real estate transactions is ascertaining whether the property is prone to flooding. The usual method has long been to rely on the 100-year-old flood maps of the Federal Emergency Management Agency (FEMA).

Such reliance is highly misleading. FEMA flood maps can be seriously out of date. They also reflect only historic conditions, not future flooding as a result of sea level rise and extreme precipitation. Moreover, large parts of the United States are not mapped at all.