Learn how to interpret our interactive flood maps to understand a property’s history of flooding, its current and future risk, and risk to the larger community.
With Risk Factor, you can unlock access to a variety of interactive maps to help better understand a property’s risk. To provide a fulsome understanding of a property’s flood risk, reports include 3 interactive flood maps- Current & Future Risk, Historic Risk, and Community Risk. View these maps by clicking Explore on map under the corresponding section name in the Flood Risk Report or use the navigation bar to select the Flood Maps tab.
Current & Future Risk
The First Street Foundation Flood Model can determine the likelihood of a flood reaching a minimum depth in a given year, known as an annual flood likelihood, or annual probability. An annual probability is the chance of something happening at least once within a specific, singular year. Risk Factor® includes three annual probabilities: the current year, 15 years in the future, and 30 years in the future. Due to changes in the environment, the depth and extent of flooding projected if a very rare flood event were to occur in 15 or 30 years differ from the depth and extent of flooding projected if that same event occurred this year. Explore flood risk by year to understand how environmental changes impact risk.
Flood scenarios describe the recurrence interval of floods. The average number of years between floods of a certain size is the recurrence interval or return period. For example, in any given year there is a 1-in-500 (0.2%) chance that this area will suffer severe flooding. Flood scenarios are used to categorize the likelihood of different severities of flooding. Lower probabilities (0.2%, 1%) represent deeper floods that are less likely to occur, but more likely to reach a building and cause greater damage.
Our Flood Model has recreated 57 major river and storm surge floods in the U.S. from 2001. The floods are modeled simulations recreated and calibrated using recorded flood data and validated against open federal flood claim data. The floods recreated broadly fall into two categories: coastal and inland. Coastal floods refer to floods caused by the storm surge of tropical storms, hurricanes, and nor’easters. Inland floods refer to floods caused by overflowing rivers. Heavy rains are often associated with both types of flood events but are not modeled in the floods shown on this tool directly. To learn about the specific historic floods recreated by the First Street Foundation please review this article.
For each event, the model calculates the depth of flooding to the building, the number of buildings within the community that were impacted, and the total number of buildings impacted by the event. The depth of flooding to the building refers to the amount of water that reached the physical building structure or the center of a lot if no structures exist on it. By recreating the observed impacts of historic floods, the model can identify where, and to what depth, flooding occurred.
Even if your home is not at risk, flooding can still impact the broader social, commercial, and community infrastructure surrounding your home. Floods that impact infrastructure cut off access to utilities, affect emergency services and transportation and impact the finances of businesses and homeowners. As climate change alters the frequency and severity of extreme weather events, deteriorating infrastructure and the communities they serve will be especially vulnerable. The community risk maps allow you to learn how flooding can impact various levels of a community.
Flood risk can vary for different levels of geographies. The tabs in this section allow you to compare how risk can vary between neighborhoods, zip codes, cities, and counties. The location is automatically set to show risk at the lowest of geography available, which is either the neighborhood or zip code. All properties have information available at the zip code and county level but not necessarily for the neighborhood.
- Overall: Risk is determined for each community category by calculating the percent of facilities with operational risk and the average expected flood depth. Once risk is determined for each of the 4 categories, overall community risk is calculated by averaging the risk for all 4 categories. Overall risk allows you to understand each category's risk to see how each contributes to the community’s overall risk. When toggling through levels of geography, category risks change to show the vulnerability associated with each location.
- Residential & Commercial: Residential and commercial risk is calculated the same way. For residential risk, the number of residential properties at risk is calculated and compared to the total number of properties within that location to determine the area’s proportion of residential properties at risk. The same method is used to determine an area's proportion of commercial properties at risk.
- Infrastructure and Social: Infrastructure considers flood risk to utilities, emergency services, and transportation. Social risk considers the impact of flooding on schools, historic and government buildings, places of worship, and museums. Infrastructure and social risk are determined based on the percent of structures and the depth of flooding that causes a facility to be flooded at a depth that exceeds the functionality threshold, causing operational risk. Similarly, the depth of flooding that causes a certain percentage of social buildings to have operational risk is used to determine a community’s social risk.
- Filter by Risk Levels: Community Risk ranks can vary within a category depending on a structure's elevation or distance to water sources, such as lakes, rivers, or oceans. To view infrastructures by the level of risk, select "Filter by level."
- Filter by Infrastructure, Filter by Social: When a facility is flooded to the point where it can no longer function as intended, it has operational risk. These thresholds vary depending on the type of facility, as different facilities can withstand different depths of flooding while still maintaining some level of functionality. For a deeper dive into infrastructure and social categorical risk, you can review specific structures at risk within a category by filtering the map to only show buildings of a certain type. For example, when viewing community infrastructure risk, you can filter the map to see risk to emergency services by only toggling fire stations, police stations, and hospitals.
- Flood damages explained
- Historic Flood Methodology - Which properties have been affected by historic floods?
- Community methodology - Is your community at risk of flooding?