Climate Data Methodology

When buying a new place or selling your current home, it’s important to understand how climate change and environmental risks could impact your home or neighborhood. Redfin has partnered with leading climate non-profit First Street, to provide home searchers with comprehensive climate risk information for every zip code, neighborhood, city, and county in the contiguous U.S. First Street develops and publishes free, peer-reviewed climate risk data in collaboration with climate science leaders.

All of Redfin’s climate risk information comes from First Street’s Risk Factor™ tool, which analyzes five major climate risks using First Street climate models: Flooding, wildfires, hurricane winds, air pollution, and extreme heat. All data shows current risks, as well as risks in 30 years based on dozens of carbon emissions scenarios.

Learn below how First Street developed their risk information and models, and how you can interpret the information to inform your own home buying or selling experience.

Flood Factor® Methodology

To help home searchers understand the growing and changing flood risks, First Street developed Flood Factor®, a free flood risk tool that provides a risk score using the First Street Flood Model and First Street Precipitation Model.

Flood Factor® determines current and future flood risks from all major causes for any location in the United States and Puerto Rico. The major causes of flooding are rainfall, overflowing rivers and streams, high tides, and storm surges.

To calculate how flood risks are changing, Flood Factor® analyzes climate models that provide future sea level rise and heavy precipitation scenarios, alongside carbon emissions.

Flood Factor® rates properties based on the likelihood of flooding and/or the maximum flood depth over the next 30 years. Risks are rated on a scale from 1-10.

Flood Factor® score ranges:

• 1 (minimal risk)
• 2 (minor risk)
• 3 -4 (moderate risk)
• 5 -6 (major risk)
• 7-8 (severe risk)
• 9 - 10 (extreme risk)

What the score means

A property’s Flood Factor® is an indicator of its current and future risk of flooding over the next 30 years. Properties with a higher Flood Factor® are more likely to experience flooding or high floods. Learn more about the Flood Factor® methodology.

Fire Factor® Methodology

To help consumers understand how wildfire risks are changing, First Street developed Fire Factor®, a free fire-behavior based tool that provides a risk score using the First Street Wildfire Model. The Model was developed in collaboration with the Pyregence Consortium.

Fire Factor® determines a specific location’s probabilistic risk of wildfire based on vegetation, topography, historic observations, and future temperatures and precipitation patterns. It assesses the real-world conditions that create wildfires and then estimates fire likelihood and severity over 30 years based on 150 million simulated possible wildfire events.

To simplify this information for homeowners, Fire Factor® rates properties based on the likelihood of being in a wildfire over the next 30 years. Risks are rated on a scale from 1-10.

Fire Factor® score ranges:

• 1 (minimal risk)
• 2 (minor risk)
• 3 -4 (moderate risk)
• 5 -6 (major risk)
• 7-8 (severe risk)
• 9 - 10 (extreme risk)

What the score means

A property’s Fire Factor® is an indicator of its current and future risk of being in a wildfire over the next 30 years. A score of 1 means a location is expected to have a 0% chance of being in a wildfire; a score of 10 means a location is expected to have a 36%+ chance of being in a wildfire. Learn more about the Fire Factor® methodology.

Does Fire Factor account for my home’s wildfire protections?

In partnership with Arup, Fire Factor® includes a home vulnerability estimate that provides homeowners with the probability that their home will ignite if a wildfire reaches their property. This estimate uses satellite imagery, public real estate and tax assessor records, and government information to approximate home protections like defensible spaces.

Wind Factor® Methodology

A changing environment means higher temperatures and unstable humidity, creating conditions ideal for tropical storms and hurricanes. To help consumers understand how climate change is impacting tropical storm (including hurricane) wind risks across the U.S., First Street developed Wind Factor™️, a free tool that provides a risk score using the First Street Wind Model.

The Wind Model is geospatially-varying, meaning it considers how a location’s likely exposure to winds is affected by climate change. It builds a forecast of likely wind speeds using government data, climate models, historical data, and hurricane simulations. Environmental changes are also integral to the model. Lastly, to provide wind risks at a property-level basis, Wind Factor™️ accounts for the roughness of the topography surrounding a building.

Wind Factor™️ rates properties based on the likelihood of experiencing tropical storm (including hurricane) winds over the next 30 years. Risks are rated on a scale from 1-10.

Wind Factor® score ranges:

• 1 (minimal risk)
• 2 (minor risk)
• 3 -4 (moderate risk)
• 5 -6 (major risk)
• 7-8 (severe risk)
• 9 - 10 (extreme risk)

What the score means

A property’s Wind Factor™️ is an indicator of its current and future likelihood of experiencing storm winds over the next 30 years. A score of 1 means a location is expected to experience winds from ranging 17-38 mph; a score of 10 means a location is expected to see winds ranging from 117-270+ mph.

Wind Factor™️ only estimates tropical storm (including hurricane) risks, and doesn’t account for tornadoes or other strong storm types. Learn more about the Wind Factor™️ methodology.

What about hurricane damage costs?

In collaboration with Arup, Wind Factor™️ estimates a property’s average annual loss (AAL), or the average cost a home bould expect over many years on a per-year basis.

Air Factor® Methodology

To help consumers understand the growing and changing air quality risks around the country, First Street developed Air Factor™, a free air quality tool that provides a risk score using the First Street Air Quality Model.

Air Factor™ analyzes the two most common harmful air pollutants: fine particulate matter (PM2.5), and ozone. The model builds a forecast of the expected annual number of poor air quality days (AQI of 100+) as defined by the Air Quality Index (AQI) using chemical and particle transport models from the National Oceanic and Atmospheric Association (NOAA), Environmental Protection Agency (EPA), climate models from the WCRP CMIP6, and wildfires from the First Street Wildfire Model. Local variation in air quality is driven by high resolution climate variation, proximity to wildfire activity, and other emission sources.

Air Factor™ rates properties based on the number of poor air quality days expected under current environmental conditions and the number expected over the next 30 years. Risks are rated on a scale from 1-10.

Air Factor® score ranges:

• 1 (minimal risk)
• 2 (minor risk)
• 3 -4 (moderate risk)
• 5 -6 (major risk)
• 7-8 (severe risk)
• 9 - 10 (extreme risk)

Air Factor™ is a climate-adjusted model, which means it considers how a location’s likely exposure to ozone and particulate matter is affected by rising temperatures and changing humidity levels. Outdoor air quality levels are combined with property characteristics like insulation and air filter ratings to provide an understanding of indoor air quality during poor outdoor air quality days.

What the score means

A property’s Air Factor™ is an indicator of its current and future risk of air pollution from fine particulate matter and/or ozone over the next 30 years. A score of 1 means a location is expected to have zero annual poor air quality days; a score of 10 means a location is expected to have 21+ annual poor air quality days. Learn more about the Air Factor™ methodology.

Does Air Factor™ account for indoor air quality?

Air Factor™ accounts for both outdoor and indoor air quality. In conjunction with Arup, First Street has developed an estimate of indoor air quality levels for every building affected by poor air quality days. Indoor air quality days are categorized on the same AQI categories that are used for outdoor air quality. A building’s filtration system, insulation, and presence of air purifiers all impact indoor air quality levels.

The First Street’s Air Quality Model combines industry standards and user inputted data on building characteristics to estimate indoor air quality levels from outdoor air quality levels.

Heat Factor® Methodology

To help consumers understand how rising temperatures will affect their home, First Street developed Heat Factor®, a free tool that provides a heat risk score using the First Street Air Heat Model.

The Heat Model is a spatial temperature model that shows a location's exposure to extreme heat events based on surface temperature, topography, land cover, tree canopy, and humidity. Equipped with leading carbon emission and warming models, the Heat Model predicts how temperatures in a location are expected to change over 30 years.

An important part of the Heat Model is identifying what it means for a certain area to be hot. This is because hot temperatures are relative – you would never expect Portland, ME to see temperatures of 110ºF, but locals would reasonably call a 90ºF day “hot.” These are called “local hot days.” The model determines a certain area’s “local hot day” threshold to calculate how the frequency of hot days will change in the future and incorporates that into the Heat Factor® score.

Heat Factor® rates properties based on the likelihood of experiencing extreme heat over the next 30 years. Risks are rated on a scale from 1-10.

Heat Factor® score ranges:

• 1 (minimal risk)
• 2 (minor risk)
• 3 -4 (moderate risk)
• 5 -6 (major risk)
• 7-8 (severe risk)
• 9 - 10 (extreme risk)

What the score means

A property’s Heat Factor® is an indicator of its current and future risk of experiencing extreme heat over the next 30 years. A score of 1 means a location is expected to see maximum annual temperatures of less than 80ºF; a score of 10 means a location is expected to see maximum annual temperatures of greater than 110ºF. Detailed reports provide the number of days a property is estimated to experience these temperatures and if they are considered 'local hot days.'Learn more about the Heat Factor® methodology.

This page is for informational purposes only and is not a substitute for professional advice from a medical provider. Consumers should independently verify any claim, agency, or service mentioned. Learn more about our Editorial Guidelines here.