Learn about the data used to calculate a property’s Flood Factor.
Property Flood Factors
A property's Flood Factor is an indicator of its comprehensive flood risk, ranging from 1–10. Properties with higher Flood Factors are either more likely to flood, more likely to experience high floods, or both.
Calculation of Flood Factor scores
That data on Flood Factor comes from the First Street Foundation Flood Model, a nationwide flood model that calculates the likelihood of a flood based on a location’s history and geographic information, such as elevation, climate, proximity to water, and adaptation measures.
A property’s Flood Factor is determined by its likelihood of flooding and the potential depth of that flood. Because flood risks accumulate over time, it specifically looks at the likelihood of water reaching the building, or center of an empty lot, at least once within the next 30 years.
Flood Factor scores increase as the 30-year cumulative flood likelihood increases, or as the projected depth of flooding increases. Properties with a less than 0.2% chance of experiencing any depth of flooding in any year within the next 30 years are considered to have minimal risk or a Flood Factor of 1.
Flood Factor Matrix
Properties more likely to experience a flood with a greater depth have higher Flood Factors.
For example, a property with an 8% chance of flooding 16 inches at least once within 30 years would have a Major Flood Factor of 5. A property with more than a 96% chance of any depth of flooding would have a Flood Factor of 7 or greater.
The First Street Foundation is continuously working to refine its flood model methodology and incorporate new information into Flood Factor. Flood Factor is updated on a quarterly basis, while the Flood Model is updated annually. Sign up for our newsletter to learn about updates as they become available by clicking or tapping here.