Flood Factor scores are based on the depth and likelihood of floodwater reaching the physical structure of a home.

The data used to calculate a property's 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, changes in the environment, proximity to water, and adaptation measures. Use Risk Factor™ to find property-specific flood risk assessments for any U.S. address.

Calculation of Flood Factor scores

A property's Flood Factor is an indicator of its comprehensive, thirty-year risk of flooding from rainfall, overflowing rivers and streams, high tides, and storm surge, ranging from 1–10. Properties with higher Flood Factors are either more likely to flood, more likely to experience high floods, or both. 

The First Street Foundation Flood Model is used to determine the likelihood of a flood occurring within a given year and the projected depth of a flood. 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 1 inch of water reaching the building footprint of a home at least once within the next 30 years. Flood Factor scores increase as the likelihood of flooding increases, the projected depth of flooding, of both over the lifetime of a 30-year mortgage. 

Flood Factor Matrix

Properties more likely to flood at a greater depth have higher Flood Factors. 

Properties with less than 0.2% chance of flood water reaching the building footprint in every year analyzed are considered to have minimal risk or a Flood Factor of 1. While it is still possible for properties with a Flood Factor of 1 to flood, they are not included in the Flood Factor matrix. In the Flood Factor Matrix below you can visualize how Flood Factors increase as the depth and likelihood of flooding increases. 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. 

• 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 6% 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.

Please note that only FEMA maps are used to determine flood insurance and building code requirements, not Flood Factor scores. Additionally, FEMA zone designations are not a factor in calculations used to determine a Flood Factor score. 

Ensuring scientific accuracy

The creation of the First Street Foundation Flood Model required an unprecedented partnership of more than 80 world-renowned scientists, technologists and analysts. Methods used in the Flood Model have undergone an expert academic panel review and have been submitted to scientific peer-review journals. Where possible, data has been validated against historic flood reports and FEMA flood claims.The data the model produces undergoes multiple reviews and must pass comprehensive check-points before being made publicly available.

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Flood Model Methodology - Calculating property-level risk

Flood Factor probabilities - The likelihood of water reaching a home

Why a property's FEMA zone does NOT impact its Flood Factor

Data sources used to determine a property's Flood Factor

Risk Factor shows a property's annual and cumulative chance of flooding. Annual probability is the likelihood of flooding in a single year. Cumulative probability is the chance of flooding over multiple years.

Risk Factor™ is a free online tool created by the nonprofit First Street Foundation® that makes it easy for Americans to find their property’s risk of flooding and understand how flood risks are changing because of a changing environment. Use Risk Factor to learn the annual and cumulative likelihood of water reaching your home so you can prepare for and mitigate risks before they become a reality.

About probabilities

A probability is a measure of how likely something is to happen. It is often expressed as a percentage, with 100% meaning something will definitely happen, and 0% meaning something will definitely not happen. 

For example, flipping a coin has two possible outcomes: heads or tails. There is a 50% chance a flipped coin will land on heads, and a 50% chance it will land on tails.

Annual and cumulative probabilities

An annual probability is the chance of something happening at least once within a specific, singular year. Flood Factor® includes three annual probabilities: the current year, 15 years in the future, and 30 years in the future.

A cumulative probability is the chance of something happening at least once over the course of multiple years. Flood Factor includes two cumulative probabilities: the next 15 years and the next 30 years.

For example, imagine each coin flip represented a year, and you wanted to know the chance of the coin landing on heads once within two flips. That would be its two-year cumulative probability. To calculate this, you have to find all possible outcomes and identify how many outcomes include the coin landing on heads. In this case, there is a 50% annual chance of the coin landing on heads, and a 75% cumulative chance of the coin landing on heads at least once within two “years” (coin flips).

Probabilities on Risk Factor

Flood Factor uses data from the First Street Foundation Flood Model to determine a location’s annual and cumulative likelihood of flooding. 

The model considers inputs such as a location’s flood history and its geographic information such as elevation, climate, proximity to water, and adaptation measures, to identify its likelihood of flooding in the current year, an annual probability. The model then incorporates projected environmental changes to forecast its risk of flooding in future years, which are also annual probabilities. Using these annual probabilities, the model is then able to calculate a location’s chance of flooding over multiple years, known as its cumulative probability.

Using the example above, if a home had a 50% annual chance of flooding, it would have a 75% chance of flooding at least once within 2 years, a 96.9% chance of flooding within 5 years, and a 99.9% chance of flooding within 10 years.

Multiple probabilities

To provide a complete flood risk analysis, Flood Factor calculates multiple annual  probabilities, 0.2%, 1%, 10%, 20%, 50%, which consider different depth scenarios. Lower probabilities represent deeper floods that are less likely to occur, but more likely to reach a building and cause greater damage.
In an earlier example, there was a 50% annual chance that a flood of some depth would occur and reach the home. But perhaps this flood is very shallow, and while it can damage the yard, it does not pose a significant threat to the home. That same home might have a 10% chance of experiencing a more extreme flood that is less likely to occur but more likely to cause damage.

Defining a low or high probability

Although the probabilities on Flood Factor may seem small or unlikely, having any chance of flooding is significant, especially given how risk accumulates over time. A home that only has a 1% chance of flooding this year, for example, has a 26% chance of flooding over 30 years– the average life of a mortgage.

 See how other annual probabilities accumulate over time on weather.gov.

Learn more

How is my Flood Factor calculated?

Greater depths of flooding cause more damage

How does Risk Factor account for uncertain future climates?

FEMA and Flood Factor are different risk assessments. Flood Factor may show higher risk because it accounts for flooding from rain and the effects of climate change.

Overview

Your FEMA zone and Flood Factor® are independent risk assessments. While the findings of these models do not diverge starkly across the US, in some areas Flood Factor may show more or less flood risk than FEMA, simply because of differences in the methodologies employed. FEMA determines flood risk on the community level, their risk projections capture risk from a single 1-in-100 or 1-in-500 event from storm surge and overflowing rivers and streams. Flood Factor calculates flood risk on the property-level, accounts for changing climate conditions, and considers the risk of flooding due to high-intensity rainfall.  

As a result, Flood Factor shows a more nuanced, property-specific flood risk, as opposed to a binary in-or-out of floodplain analysis from FEMA maps. Flood Factor uses publicly available flood risk information that shows how risk will accumulate and change over time. It is most powerful when used in conjunction with FEMA flood maps and other available state and local flood risk resources, and should be viewed as complementary to FEMA flood maps, which need to be used for building and permitting purposes. Individuals can search their address on Risk Factor to find their property’s flood risk as well as their FEMA zone. 

Flood risk on Risk Factor

The methods used to create the First Street Foundation Flood Model bring together a number of resources and techniques already developed as inputs to understanding one’s flood risk. By combining these resources, the model represents flooding from multiple risks, such as rain, river, tidal and storm surge flooding, while also integrating current and future environmental considerations all at a property level.  Adding to the full picture of flood risk, the model also recreated more than one hundred coastal and inland flood events over a 20 year period (2000-2019) to provide estimates of past flooding likelihoods.  This combination of precision and national scope allow for a more comprehensive flood risk tool than currently available. 

FEMA flood risk

To date, the standard national comparison for flood risk is the Federal Emergency Management Agency’s (FEMA) Special Flood Hazard Areas (SFHA).  The FEMA SFHA models are currently the most popular flood-risk identification tool and are widely used throughout government, research, and private companies as a way to understand flood risk, price insurance premiums, and prepare for potential hazards. A property's FEMA zone designation is estimated on Flood Factor. 

The initial FEMA SFHA models are made for individual communities and are generally very high-quality, have been built to explicitly understand the risks to a standard 1-in-100 or 1-in-500 year flood event, and have been developed over many years to identify community flood risk based on local historical context. However, these models do not exist for the entire country, and their output also undergoes a series of adjustments and revisions based on local stakeholder feedback.  That means that the FEMA SFHA maps that get instituted are very rarely the same as the initial risk identified in the area. Couple that with the fact that the model is created to capture risk from a single 1-in-100 or 1-in-500 event, reliance on historical trends, and the lack of national scale, and you have opportunities for improvement in the communication of national flood risk.

Flood Factor vs FEMA

In comparison, the method used to create the flood risk visualized on Risk Factor expands flood risk mapping to the entire country by relying on an innovative Regionalized Flood Frequency Analysis (RFFA) approach. This approach makes use of traditional statistical matching techniques to model the characteristics of ungauged streams and river reaches across the country with known gauged characteristics to produce likely flow conditions with high confidence. Additionally, a core component of the model is the ability to also include pluvial (rainfall) events as probabilistic flood risks with depths and associated return periods in areas that are outside the modeled extents of FEMA studies.  Both the RFFA and pluvial flooding integrations have allowed for a model that captures risk that is generally not captured in FEMA SFHAs. 

To highlight the additional coverage of the risk identified by the First Street Foundation Flood Model, the 1-in-100 hazard layer, representing a 1% annual risk of occurrence, was compared to the same probability zones outlined by the FEMA SFHA zones. The results indicate that the Flood Model generally captures about 3 times the risk as the FEMA SFHA.  Interestingly, the two models align well along gauged river channels and FEMA SFHAs help provide a source of validation for the fluvial risk identified in the model.  However, the discrepancies indicate the practical need for the more comprehensive approach that was used to produce the statistics in this report.

The alignment of the Flood Model results with SFHAs in areas that are gauged and mapped by FEMA is important. This highlights the utility of the Flood Model as being in agreement with standard indicators of flood risk by building on trusted models, reports, and open data resources. To that point, this model relies heavily on data from the National Oceanic and Atmospheric Administration (NOAA), FEMA, the United States Geological Survey (USGS), the World Climate Research Programme (WCRP), and hundreds of local government resources.  As such, the Flood Factor risk results should be seen as an extension of existing resources developed with innovative and creative methods to comprehensively include geographic areas that may have been left out of alternative-risk models.  

Use Risk Factor to understand your risk

FEMA flood maps identify over 1.1 million miles of flood hazard areas, and while the maps can provide detailed information for homeowners on their flood risks, they are not available everywhere. Risk Factor’s national flood model shows that flood risk is more widespread in the United States, with over 26 million properties at risk over the next 30 years. Risk Factor™ also includes flood risk from extended periods of high-intensity rainfall, leading to urban stormwater flooding and storm surge. Additionally, future conditions are considered, such as sea level rise.

Without free access to accurate flood information, more Americans will unknowingly be at risk from the nation’s costliest natural disaster. Risk Factor aims to quantify and communicate America’s flood risk. By making flood risk data freely available for all, individuals and communities can prepare for and mitigate risks before they become a reality. 

Press Coverage

CNN - Flood risk is growing for US homeowners due to climate change. Current insurance rates greatly underestimate the threat, a new report finds

The New York Times - Climate Threats Could Mean Big Jumps in Insurance Costs This Year

Bloomberg - Most Americans Don’t Have Enough Flood Insurance for Climate Change

Learn more

Understand the differences between FEMA Flood Zones

How is my Flood Factor calculated?

How does Risk Factor determine flood risk if changing environmental factors are uncertain?

We are committed to accuracy and continue to grow, adapt, and change our Flood and Wildfire Models as new and better information becomes available. 

Quarterly Data Updates

At First Street Foundation®, we aim to quantify and communicate America’s climate risk. By making flood and wildfire risk data freely available for all, individuals and communities can prepare for and mitigate risks before they become a reality.

We are committed to the accuracy of our data and will continue to grow, adapt, and change our Flood and Wildfire Models as new and better information becomes available. As such, improvements to our models are included in quarterly data updates, while both the Flood Model and Wildfire Model  is updated annually. Sign up for our newsletter to learn about updates as they become available by clicking or tapping here. 

Wildfire Model Updates

May 16, 2022

• Launched wildfire risk from the First Street Foundation Wildfire Model on the newly created Risk Factor™ site, which is a free online tool that makes it easy for anyone to find their property’s past, present, and future flood and wildfire risk.

Flood Model Updates

May 16, 2022

• Expanded the First Street Foundation Model to include Hawaii, Alaska, and Puerto Rico
• Improve address matching to allow for more flexibility in showing flood risk to properties other than single family residential homes.
• Updated our scoring methodology. The specific depth and likelihood of flooding expected to reach a property is now used to determine the boundaries for each level of flood risk.

April 23, 2021

• Updated building characteristics (i.e. # of stories, units, basements, ground floor elevation) in some areas to more accurately reflect current findings which improved accuracy for default annual loss calculations for those properties.
• Updated property FEMA zones based on user-provided documentation
• Expanded historic flood methodologies to improve accuracy of 3 historic hurricanes (Harvey, Florence, and Matthew). The updated models now include additional flooding caused by rainfall.
• Incorporated new high-resolution LiDAR elevation data provided by local officials in the Dallas-Fort Worth metro area
• Updated statistics for 1,600 previously unavailable properties in Georgia

February 22, 2021

• Added annual flood damage estimates for residential properties at risk 
• Added total annual flood damage estimates for neighborhoods, zip codes, cities, and counties

January 18, 2021

• Updated Flood Factors that better represent wetland conditions and incorporate the latest geographic data.
• Improved the accuracy and extents of flooding for several historic floods, including Hurricane Katrina.
• Analyzed and added millions of new properties to Flood Factor with improved statistical methods and issues identified by users.
• Updated FEMA designations to reflect LOMAs and LOMCs submitted by users in addition to more accurate FEMA zone data obtained from FEMA. 

Oct 30, 2020

• Improved our Flood Model by determining a property’s Flood Factor is most accurate when calculated based on the building’s footprint, or outline. As a result the center of map pins have been moved from the center of a property to the building footprint.
• Added new property addresses via Mapbox in order to provide Flood Factors for as many properties as possible.
• Widened the boundary for coastal properties in order to fully capture all possible flood risk scenarios for these areas.
• Adjusted Flood Factor for properties in South East Florida to reflect all flood risks scenarios a property faces.
• Updated 2035 map flood layers for some areas.

September 16, 2020

• Added 2 million new properties on Flood Factor.
• Updated Flood Factor scores for some properties based on new and improved data on flood risk.
• Made additional coastal cities and counties with cleaner coastal flood layer visuals available.
• Removed areas that are currently under review based on new and improved flood risk data.

Site Improvements

Ongoing site enhancements aim to provide our users with the best experience possible on riskfactor.com. 

May 16, 2022

• Created Risk Factor™ is a free, online tool that makes it easy for anyone to find their property’s past, present, and future flood and wildfire risk
• Launched Fire Factor™, the first public, peer-reviewed wildfire model to show how property-level flood risks change over time because of the environment

March 19, 2021

• Improved site and search speeds across Flood Factor. 
• Added new videos explaining Flood Factor fundamentals and the differences between Flood Factor and FEMA. 
• Modified the content on locality pages to highlight the percent of properties at risk of flooding. 
• Modeled risk on the community level to show the severity of risk threatening access to utilities, emergency services, and transportation within a neighborhood, zip code, city, and county.

February 22, 2021

• Added the average annual cost of all potential flood damages this year and 30 years from now, based on a property's flood projections and the accumulation of those expected costs over time.
• Included the “adjust building details” tool in order for users to change the various inputs, such as the estimated value of a home, presence of a basement, number of stories, and ground floor elevation, to see how these factors affect the costs associated with flood damage
• Added the total annual flood damage estimates this year, and in 30 years to neighborhood, zip code, city, county, and state pages

January 18, 2021

• Enhanced maps on desktop to expand for a fully immersive experience.

December 3, 2020

• Included a zoom bar for the score map to allow users to view Flood Factors on a neighborhood and city level. 
• Improved the Flood Factor experience on mobile devices.

November 13, 2020

• Added a pin on score maps so users can easily identify their property at any zoom level.
• Optimized Flood Factor’s load time for an even faster experience.
• Updated some coastal areas to include 50% probability. 

October 30, 2020

• Updated address information in order to improve the search experience.
• Updated map pins to be shown on top of building outlines (when possible).
• Added new and updated coastal cities and counties with cleaner coastal flood layer visuals on the Flood risk explorer in 2035 for properties in southeastern Florida.

Sep 16, 2020

• Added local Flood Factor score maps on property pages.
• Made copy updates in partnership with The Association of State Floodplain Management.

August 24, 2020

• Added the 5% likelihood of a property flooding to the flood risk explorer.
• Improved address search function on Flood Factor.

Want access to our data?

You can get access to the most comprehensive property-level flood and wildfire risk data set in existence. For commercial use or non-profits, academics, or public sector professionals needing data at a property-level, First Street Foundation provides access to property specific flood risk statistics for purchase. Learn more. 

For nonprofits, academics, and the public sector, aggregated flood risk summary statistics are now available for public, noncommercial use through the AWS Registry of Open Data and on ESRI’s Living Atlas and Maps for Public Policy sites. Learn more.

Learn more

First Street Foundation Flood Model Methodology

First Street Foundation Wildfire Methodology 

If you believe your property’s FEMA zone is incorrect, a flood control feature is missing, or you have more information about a historic flood please reach out to us!

Flood Factor® is a free online tool created by the nonprofit First Street Foundation® that makes it easy for Americans to find their property’s risk of flooding and understand how flood risks are changing because of a changing environment. First Street Foundation’s flood model is, built upon the excellent work of FEMA, NOAA, NASA, USGS, and many others, as well as the established and peer-reviewed work of all of our flood model partners. Please let us know if RiskFactor.com is displaying an incorrect FEMA zone, a flood control feature is missing, or if you have additional information regarding the impact of a historic flood. We are continuously working to refine our flood model methodology and incorporate new information into Flood Factor to ensure we are providing the best, most accurate picture of flood risk to our users.

Share information

The projections shown on Flood Factor come from the First Street Foundation Flood Model. We have made our flood model’s full technical methodology available to the public because we support scientific collaboration and data transparency. Like all flood models, its projections are intended to help provide a fuller understanding of flood risks, and we encourage you to supplement this information with additional data. We are committed to the accuracy of our data and will continue to grow, adapt, and incorporate feedback and expand our model over time, including an annual data update.

Data that will help improve the Flood Model

You know your property better than anyone! If you have information you think might be helpful to improve our Flood Model, please let us know by submitting a request through our contact forms. Please note that this information will not change your property's Flood Factor, but it can help improve the accuracy of the First Street Foundation Flood Model, and the information shown on Flood Factor. In order to improve our Flood Model, please reach out if you notice any of the following issues:

Incorrect FEMA Zone

If you believe Flood Factor has listed the incorrect FEMA flood zone for your property, please submit a Letter of Map Amendment (LOMA). The FEMA zone information listed on Risk Factor™ is currently an estimated zone. We recommend working directly with an outside company to acquire the Flood Determination Certificate for a property or to get the determinations reversed with a Letter of Map Amendment. Once submitted through our help center form, we can correct this information.

Missing flood control features

Our team is continuing to conduct research on flood control projects around the country and will be continually updating the model based on new information. While our database contains 23,000 features today, we acknowledge there are more to include, and value your input!

If you have knowledge of specific completed projects, precise service area extents-of-flood adaptation infrastructure, or spatial data on flood adaptation infrastructure,  please help the team by providing any level of detail you can here. Certain information about flood control projects are particularly useful, such as: 

• Name of the flood control project
• Entity in charge of the project (local government, FEMA, USACE, etc.)
• Address or specific location  
• Images
• Links to local, state, or federal documents outlining project details, including the flood event it protects for
• A map showing the geographic area the project protects, including the physical location of the flood control project

New projects can be included for our next update to improve the model! If you would like to read about examples of flood control projects and how gray infrastructure works to alleviate flooding please review this article. 

Example of a levee; an embankment built to prevent the overflow of a river. Levees can also be built along low-lying coastal areas.

Missing historic flooding event

Flood Factor uses data from the First Street Foundation, which has modeled 57 major river and storm surge floods in the U.S. from  2001 on, and is continually adding more. Historic events in the First Street Foundation Flood Model are recreated using hydraulic models and public data sources. Historic river flooding events are recreated by analyzing historical USGS stream gauge readings during identified flood events and then compared to recorded high water marks and insurance claims of flooding made during that event. Coastal flooding events are recreated by analyzing storm surge, tides, coastal circulation, wind-generated waves, and geospatial analysis for specific storms, such as Hurricane Katrina. The recreation is then compared to recorded high water marks during the event. 

Aftermath of Hurricane Gustav - August 2008

If you have knowledge of specific historic flooding, we'd love to hear from you. We will investigate historic flooding this area further and incorporate any new events determined into our future update. 

In order to include historic events in our Flood Model please reach out to us through our Help Center and provide:

• Dates the event took place
• Location of historic flooding
• Any pictures that may show the depth and damage of the flood
• News articles that describe the flooding your property experienced 

Naming Mismatch

We understand you may have questions regarding names of locations related to your property. The First Street Foundation Flood Model matches parcel data from official government sources to address data collected from commercial sources. Naming conventions attached to specific parcels and addresses may not exactly match, resulting in naming discrepancies. Here is a link to the methodology behind our research.

If you have knowledge of specific location names, we'd love to hear from you. Please submit a ticket through the Risk Factor Help Center that includes:

• A corrected address that includes the house number, street address, zip code, city, and state
• The incorrect address listed on FloodFactor.com 

We will review the issue further and be sure to update any issues found during a future update. Please take a look at how we update Risk Factor data.

Learn more

Flood Model Methodology - Calculating property-level risk

Learn how property-specific heat risk is determined.

The expected change in average high temperature is influenced by the changing environment. A changing environment means higher average temperatures and increased humidity, which has a compounding effect on heat indexes, or “feels like” temperatures, that make risky health impacts more likely. As the global temperature rises at a faster rate than ever recorded, it's important to understand what factors contribute to heat risk.

A property's Heat Factor is an indicator of its risk to extreme heat exposure over the next thirty years.  The model assigns each property a Heat Factor, ranging from 1 (minimal risk) to 10 (extreme risk). Heat Factors are based on the current average daily high temperature and humidity of a property’s specific location during the hottest month of the year, and considers how it’s expected to grow over the next 30 years. Properties with higher Heat Factors have higher current, and/or future “feels like” temperatures.

The impact of the changing environment 

Climate change influences average high temperatures and increases humidity, causing heat risks to change. As average high temperatures increase around the globe, hot days increase in both frequency and intensity. Conservative estimates show that temperatures across the United States are projected to increase by at least 2.5 °F over the next 30 years. An increase in temperature can also lead to an increase in humidity in some areas. The First Street Foundation Extreme Heat Model (the model used by Heat Factor) uses the RCP 4.5 carbon emissions scenario to forecast how temperatures will change 30 years from now. This allows the model to predict temperatures 30 years from now in a way that meets the rigorous standard of scientific peer review.

Local variability

The amount of change in heat risk is influenced by local factors such as an area's landscape, vegetation, elevation, urbanization, and distance to water bodies and coastlines. These factors explain why some places will experience large changes in heat risk while others will experience more mild changes. For example, the urban heat island effect is a common example of how temperatures vary significantly. This effect describes how temperatures tend to be warmer in urban areas, compared to the more leafy, and less dense, suburban areas of a given city. 

Neighboring towns and cities can have very different temperatures due to local characteristics. It's easiest to identify local differences when temperatures are the warmest. For this reason, the model looks at temperatures and humidity during the hottest months of the year, which is July for most areas and in some areas August. Historic temperature records are used to create a map of average high temperatures across the U.S and compare how temperatures vary from property to property within a community. 

The calculation of property-specific Heat Factors 

Scoring system for properties 

Temperatures during the hottest month of the year are reviewed for each property’s specific location. For the majority of areas, the hottest month of the year is July and in some areas is August. The daily high “feels like” temperatures during this month are then averaged to determine the average high daily temperature for a property’s specific location this year, and 30 years into the future. Heat index, also known as a “feels like” temperature, is a measure used to indicate the level of discomfort the average person is thought to experience as a result of the combined effects of the temperature and humidity in the air.

This 30 year average high temperature represents how hot the specific location of a property is and how much the temperature is expected to change at that given location. Properties with higher Heat Factors have higher current, and/or future “feels like” temperatures during the summer months.

These temperatures are then compared to the safety thresholds for heat index informed by the National Weather Service. “Health caution” days are considered to be temperatures around 80°F and associated with relatively minor consequences, such as fatigue. Days above 125°F are considered “Extreme Danger” as they’re associated with life threatening effects such as heat stroke.

Heat Factor Scores

How hot a specific location is today and how much that temperature is expected to grow is used to determine the boundaries for each level of heat risk. These boundaries produce a set of rules that can be used to understand why one property may have a Heat Factor of 4 while another has a Heat Factor of 7. If the current average high temperature and the average high temperature in 30 years is:

Ensuring scientific accuracy

The peer-reviewed First Street Foundation Extreme Heat Model is a first of its kind, nationwide, spatial temperature model that shows a specific location’s exposure to extreme heat events based on the temperature, topography, land cover, and humidity in the surrounding area. It builds off of decades of peer-reviewed research and forecasts how heat effects will change over time due to changes in the environment.

The development of the model required an unprecedented partnership with top climate scientists and modelers from leading organizations along with top data scientists and technologists to ensure the data is accessible, accurate and actionable. Where possible, data has been validated against historic temperature data and government records. All methods used by the First Street Foundation Extreme Heat Model have been submitted to scientific peer-review journals. Use Risk Factor to find property-specific heat risk assessments for any U.S. address.

Learn more

The methodology behind the model used by Heat Factor

Data sources used to determine Heat Factors

Heat Factor - Frequently asked questions (FAQ)

Answers to frequently asked questions regarding a property’s Heat Factor, the cost of heat, and health risks associated with increasing temperatures. 

Heat Factor is a free online tool created by the nonprofit First Street Foundation that makes it easy for Americans to find their property’s exposure to extreme heat events and understand how heat effects will change over time due to changes in the environment. As global temperatures rise at the fastest rates ever recorded, it's important to understand what factors contribute to heat risk. Use Risk Factor to find property-specific heat risk assessments for any U.S. address.

What is Heat Factor?

A property's Heat Factor is an indicator of its risk to extreme heat exposure over the next thirty years.  The model assigns each property a Heat Factor, ranging from 1 (minimal risk) to 10 (extreme risk). Heat Factors are based on the current average daily high temperature and humidity of a property’s specific location, and how much the average daily high temperature and humidity in that location is expected to grow over the next 30 years. The expected change in average high temperature is influenced by the changing environment. A changing environment means higher average temperatures and increased humidity, which has a compounding effect on heat indexes that make risky health impacts more likely. As the global temperature rises at a faster rate than at any point in the planet’s geological record, it is important to understand what factors contribute to heat risk. Learn more about the environmental factors increasing heat risk. Learn more.

How accurate is Heat Factor?

The peer-reviewed First Street Foundation Heat Model is a first of its kind, nationwide, spatial temperature model that shows the exposure of a specific location to extreme heat events based on the temperature, topography, land cover, and humidity in the surrounding area. The development of the model required an unprecedented partnership with top climate scientists and modelers from leading organizations along with top data scientists and technologists to ensure the data is accessible, accurate and actionable. 

Where possible, data has been validated against historic temperature records and government records. All methods used by the First Street Foundation Extreme Heat Model have been submitted to scientific peer-review journals.

How can I remove a property from Heat Factor?

Heat Factor is a product of the First Street Foundation, a non-profit committed to making climate risk information free and accessible to all.  We are committed to the accuracy of our data and we’re continuously working to refine our Extreme Heat Model methodology and incorporate new information into Heat Factor. When additional information is submitted, it is reviewed, and if appropriate, incorporated into the model, and shown on Heat Factor during a scheduled update. 

However, Heat Factors are not assigned on a one-off basis, rather they’re derived from the inputs that go into our Extreme Heat Model. These inputs come from publicly available data, therefore, properties cannot be removed directly through Heat Factor. Therefore, the only way a property’s Heat Factor can change is if new information is submitted that changes the underlying inputs used in our Extreme Heat Model. We encourage you to share information that may impact the inputs used in our heat by submitting an email.

How often is Heat Factor updated?

The Risk Factor team is continuously working to refine the Extreme Heat Model methodology and incorporate new information into Heat Factor. While the Heat Factor experience is updated regularly, a full Extreme Heat Model refresh occurs annually. Sign up for our newsletter to learn about updates as they become available.

What are heat islands? 

Heat islands are urban or metropolitan areas that are much warmer than the surrounding area due to human activities. The temperature difference is usually larger at night than during the day, greatly increasing the cost of cooling for homes and businesses located in a heat island. Nevertheless, daytime temperatures within a heat island can vary by as much as 7 degrees from the surrounding neighborhood or area. Common causes of the heat island effect include; neighborhood construction materials, city planning and layout, distance to water bodies and vegetation, and human activities. Learn more.

How can I reduce my risk? 

Heat-related illnesses are caused by water loss,  excess physical activity, and reduced nutrients which causes your core temperature to rise. Being prepared will allow you and your loved ones to remain safe during extreme heat events. Before an extreme heat event, learn how to recognize and prevent heat-related illness.

To mitigate the negative effects associated with exposure to extreme heat, explore energy efficient ways to prepare your home for the next heat wave. Making the right investments to protect your home can protect you from dangerous heat illness on extremely hot days. Learn more.

How much can heat cost? 

The amount of energy required to cool a home depends on the number of cooling days estimated for a property and the degrees of cooling required to maintain a consistent indoor temperature. The number of cooling days refers to the number of days when the temperature is warmer than 70°F and therefore requires the use of air conditioning to maintain a comfortable indoor temperature. The warmer the temperature outside the greater degrees of cooling required. 

The cost to cool a home depends on the temperature outdoors and specific property characteristics such as the number of bedrooms, age of the home, and square footage. The price each household will pay for electricity varies depending on where the local grid is supplied, the companies that supply an area, and number of homes. Using data on energy rates from Energy Information Administration (EIA), a property’s yearly energy consumption is translated into cost based on energy rates in that area. Learn more.

Please note, cooling days on Risk Factor only consider air conditioning, not other cooling devices such as fans. 

How can heat affect health?

Extreme heat can lead to dehydration, fatigue, heat stroke, heat exhaustion, heat cramps, which occur as a result of the body’s inability to cool itself relative to the surrounding environment when heat indexes exceed certain physical thresholds. Heat Index Values are a measure of how hot it feels outside when incorporating relative humidity. 

Heat Index temperatures around 80 degrees are  associated with relatively minor consequences, such as fatigue. Once the heat index exceeds 90 degrees, heat-related illnesses such as cramps, heat exhaustion, and heat stroke become possible. At a heat index of 100 degrees, early stage heat-related illnesses such as cramps and heat exhaustion go from being possible to being likely for anyone who is exposed to heat for a prolonged period of time.  While heat related illnesses can cause death at any heat index, a heat index above 125 degrees is particularly risky. At these temperatures heat stroke is likely to occur for any individual exposed to these temperatures for a prolonged period of time. Learn more.