Learn about why nearby homes can have different flood risks.
About Flood Factor rankings
Because Flood Factors are determined by potential flood depths and 30-year flood likelihoods, rankings often vary across neighborhoods. Even next door neighbors can have significant differences in flood risks, largely due to differences in elevation, proximity to water or wetlands, and proximity to flood risk reduction projects.
Ranks vary because of differences in flood risks
If you’re not sure why your home’s Flood Factor differs from your neighbor’s, one way to understand differences in risks is to switch to the map view on the flood risk explorer. If you zoom in close enough, you can see both building outlines as well as different flood scenarios. Properties with minimal Flood Factors shouldn’t show any flood water reaching the building outline in any flood scenario. Buildings in contact with deeper floods, or those with higher probabilities of flooding, will have higher Flood Factors.
Flood risks vary for a wide variety of reasons
A property’s Flood Factor is determined by the likelihood and of floodwater reaching the largest building on a property. If building information is unavailable, like for vacant lots, flood risks are analyzed against the center of the property. As a result, even seemingly-minor differences between similar homes can lead to differences in flood risks and Flood Factors.
Common reasons for differences in flood risks
Proximity to water
If water is coming from a nearby lake, river, or bay, a home closer to that water source may be more likely to flood, or more likely to experience a deeper flood.
Differences in elevation
Imagine two similar homes located next to each other. House A is located on the highest area on its lot, about a foot higher than the rest of the land. House B is located on a flat property. If a flood occurs, water would be more likely to reach house B, so that home has both a higher flood risk and a higher Flood Factor. While areas of House A’s property might flood, Flood Factors are determined by water reaching the building itself.
Local flood risk reduction projects (adaptation)
Many communities have natural or engineered structures that reduce flooding, like wetlands, levees, or seawalls. Properties near these structures benefit by having lower flood risk than properties without protection.