Learn about why nearby homes can have different flood risks. Next door neighbors can have significant differences in flood risks, due to differences in elevation, proximity to water, wetlands or 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.
The specific depth and likelihood of flooding expected to reach a property is used to determine the boundaries for each level of flood risk. These boundaries produce a set of rules that can be used to understand why one property may have a Flood Factor of 4 while another has a Flood Factor of 7. Below are general Flood Factor thresholds based on likelihood of flooding and scores increase from these thresholds based on depth of flood water so if two homes have similar likelihoods of say 26%, one could have a higher score if it’s more at risk for higher depths of flooding.
- Properties with at least an 6% chance of flooding over 30 years will have a Flood Factor of 2 or higher
- Properties with at least a 26% chance of flooding over 30 years with have a Flood Factor of 4 or higher
- Properties with at least a 80% chance of flooding over 30 years will have a Flood Factor of 5 or higher
- Properties with at least a 99% chance of flooding over 30 years will have a Flood Factor of 6 or higher
For example, a property that has a 12% chance of at least 1 inch of floodwater reaching the home will have a moderate Flood Factor of 4. In contrast, a property that has a 47% chance of at least 1 inch of floodwater reaching the home will have a major Flood Factor of 6.
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.
Without free access to accurate flood information, more Americans will unknowingly be at risk from the nation’s costliest natural disaster. By making flood risk data freely available for all, individuals and communities can prepare for and mitigate risks before they become a reality.
Search your property on RiskFactor.com to learn if your home is at risk.
How is my Flood Factor calculated?