Find answers to frequently asked questions about Community Risk.

What is Community Risk? 

In addition to damaging residential properties, flooding can impact day to day life within a community, cutting off access to utilities, emergency services, and transportation. The First Street Foundation Flood Model is used to determine the risk to infrastructure, properties, and roads from multiple types of flood events, including fluvial (river), pluvial (rain), storm surge, and tidal sources. The presence or lack of projected flooding, and the projected depth of that flooding, is used to determine community vulnerability to flood risk. The flood risk to each facility is based on the likelihood of flood waters  reaching the building footprint, or parcel centroid, of each facility, or  the center of a road -- and then combined with the expected depth of that flooding.

How are community areas defined? 

Community Risk denotes flood risk to the local services and infrastructure surrounding properties, and are grouped by  neighborhood, zip, city or municipalities, and counties. It considers flood risk across 5 different dimensions: (1) Infrastructure (utilities, airports, ports, and emergency services); (2) Residential properties; (3) Commercial properties; (4) Roads; (5) Social services (churches, schools, museums).  Because Community Risks can vary for different levels of geographies, Flood Factor allows you to compare risks between these levels. 

Communities available through Community Risk overview:

  • Neighborhoods - Encompasses macro neighborhoods, neighborhood, sub-neighborhoods and residential districts (e.g. subdivisions and apartment complexes) are not an official designation and vary in size depending on local usage
  • Zip codes are zip code tabulation  areas as provided by the U.S Census Bureau. 
  • Cities - Place (County Subdivision in New England) as provided by the US Census Bureau. Refer to a village, town, or city typically governed by a mayor and council.
  • Counties are territorial divisions of a state and are typically government units that sit below the state level. County or county-equivalents as provided by the US Census Bureau.

How do I read the Community Risk map? 

The Community Risk map allows you to easily visualize the geographic distribution of infrastructure and facilities at risk in your area. The map uses different colors to show how the flood risk level varies between areas, with grey representing minimal risk and dark red showing extreme risk.

Use the drop-down menu on the Community Risk map to see the structures at risks in your area by category. For instance, you may want to learn more about infrastructure at risk in your area. Selecting “Infrastructure” from the drop-down allows you to see how flooding can impact utilities, emergency services, and transportation in your area. For a deeper dive into categorical risks, you can select specific structures within a category. You can use the risk map tabs to toggle between different geographies to see how flood risks vary between neighborhoods, zip codes, municipalities/ cities, and counties. To view infrastructures by the level of risk, select "Filter by level." 

You can also look at which facilities specifically have operational risk over the next 30 years by clicking on the “points on map”. Within this area you can filter to show just the type of facilities you are interested in viewing. If you hover over (or click on mobile) a facility pin on the map, it will provide more details with the facility name, address and risk level. 

How can I compare risk between different locations? 

To compare the overall risk between your area and those around you, select "Compare areas." The map uses different colors to show how flood risk varies between neighboring areas. On one end of the spectrum, grey represents locations with minimal risk, while dark red shows locations with extreme risk. The map legend identifies the risk level each color on the map represents, making it easy to understand how the different colors relate to varying levels of risk.  

Is local adaptation taken into account?

The First Street Foundation Flood Model is used to determine the risk of flooding from the 4 major flood types of (tidal, pluvial, fluvial, and storm surge). Community Risk also takes into account the 100,000 adaptation features included in First Street’s Flood Model. Therefore, flood projections consider the risk-mitigating effects of levees, dams, open spaces, and other adaptation features included in the Flood Model. The model does not include personal adaptation such as sump pumps, or personal property drainage etc.

How can my home have minimal risk but my area has high flood risk? 

We understand it can be confusing if a property has a low Flood Factor yet Community Risk for your neighborhood is high. A property's Flood Factor and Community Risk scores are both  comprehensive risk assessments, which take into consideration the 30 year risk of flooding from high intensity rainfall, overflowing rivers and streams, high tides, and storm surge. 

The distinction is that Flood Factors reflect the likelihood of water reaching your individual home’s building footprint, while Community Risk determines the surrounding area’s vulnerability to flooding. Building footprints refer to the outline of a building structure on a property. Community Risk encompasses the social risk, residential risk, commercial risk, risk to infrastructure, and risk to roads of flooding within a geographic area.

Within a community, the likelihood of flooding, and the depth of flooding that causes a certain percent of facilities to have operational risk is used to determine categorical risk. Each category is given a ranking based on the percent of facilities or roads with operational risk at a given depth. The overall Community Risk encompasses the social risk, residential risk, commercial risk, risk to infrastructure and risk to roads for a given area. Once risk is determined for each of the 5 categories, overall risk for a community is calculated by averaging the risk for all 5 categories. 

What do the different risk levels mean?

Community Risks consider the Social risk, Residential risk, Commercial risk, Infrastructure risk, and risk to Roads of flooding within a geographic area, making up the 5 categories used to determine overall risk of flooding. Risk is determined based on the depth of flooding that causes a certain percent of structures to be flooded at a depth that exceeds the functionality threshold, causing operational risk. 

The distribution of these expected depths within a community are considered at intervals of 5 from 0 to 100. For instance, the depth at which 5% of facilities within an area have operational risk less than or equal to this depth, the depth at which 10% of facilities within an area have operational risk less than or equal to this depth, and so on. The depth of flooding that threatens operational risk at each interval is added, resulting in a final numerical category score for a given community. Each category is given a ranking based on the percent of facilities or roads with operational risk at a given depth. Categorical Community Risk rankings represent risk as Minimal, Minor, Moderate, Major, Severe and Extreme. Minimal risk is a case where no facilities within a category have flood risk. The total depth for each community level, neighborhood, zip code, city, and county; is then compared to the total depth for similar community levels within a state or across the country. County level risks are ranked based on how their total depth compares to counties across the county. While, neighborhood, zip code, city level risks are ranked based on how their total depth compares to communities within respective states.

Once risk is determined for each of the 5 categories, overall risk for a community is calculated by averaging the risk for all 5 categories. Overall Community Risk is also represented as Minimal, Minor, Moderate, Major, Severe and Extreme.

What is operational risk?

Operational risk refers to the loss of operational functionality for a facility. In order to determine the point where infrastructure and roads can no longer operate, infrastructure type is broken down by functionality threshold. When a facility is flooded to the point where it can no longer function as intended, or a road is flooded to a depth that makes the road unusable and unsafe, it is considered to have operational risk. These thresholds vary depending on infrastructure type, as different types of infrastructure can withstand different depths of flooding while still maintaining some level of functionality. For this reason, functionality thresholds are used to determine the operational risk to infrastructure and roads caused by flooding. Operational thresholds used are as defined in the FEMA’s HAZUS methodology.

 

Learn more

How are Community Risk levels determined? 

What data sources are used to determine Community Risk ratings?

First Street Foundation Flood Model Methodology 

 

 

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