The methodology behind the model used by Wind Factor

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First Street Foundation’s Wind Model is a first-of-its-kind model that relies on public data to determine property-specific wind risk. 

Data on Wind Factor comes from the First Street Foundation Wind Model (FSF-WM). The First Street Foundation Wind Model is focused on how climate change is impacting wind risk to structures within the US. Changes to hurricanes’ intensities and their distribution are forecast to be the largest impacts of climate change on wind risk. The model builds off of decades of scientific peer-reviewed research and forecasts how hurricanes and costs from resulting wind damages to structures will change over time due to changes in the environment.

Factoring in hurricane wind risk 

The First Street Foundation Wind Model is a geospatially-varying wind model, which means it considers how a location’s likely exposure to high-speed winds is affected by climate change’s impacts. These impacts are related to forecast changes in hurricane intensities and their tracks as well as the property’s characteristics, and use that information to assess the likely damages that would result from a property’s exposure to extreme wind.

The model builds a probabilistic forecast of the likely wind speeds for each location in the US by using multiple datasets from the National Oceanic and Atmospheric Association (NOAA), climate models from the WCRP CMIP6, and simulated hurricanes provided by Dr. Kerry Emanuel of MIT and sampled by Rhodium. 

The First Street Foundation Wind Model considers a location’s risk specifically from hurricane winds. To build an understanding of this risk, tens of thousands of synthetic, computer-modeled hurricane tracks are used to build estimates of likely wind speed under the influence of a changing climate.  For every location, the likely exposure to extreme wind is calculated for today and 30 years into the future.

The impact of climate on hurricanes

The inclusion of environmental changes that impact future wind risk is an essential part of the First Street Foundation Wind Model. The model used the WCRP CMIP6 SSP245 scenario to forecast how environmental conditions will change 30 years into the future, and how those conditions will influence hurricane intensities and tracks, and applied those forecasts to create a  property-specific wind speed forecast model. This allows the First Street Foundation Wind Model to predict winds and associated damages 30 years from now and builds upon previously-published science to create new studies that may pass the same rigorous standard of scientific peer review.

Note that while there is some recent evidence surrounding climate change’s impacts on the locations of tornadoes, convective storm wind events (such as thunderstorms), winter storms, and nor’easters, at this time those storm types’ climate-related damages are still active areas of research and are not yet included in the model. That said, tornado and thunderstorm risks are noted in the Wind Factor reports and historic information on these risks is included where available.

Correcting for local variations  

Local variations in wind speeds are driven by the roughness of the surrounding area which impacts how winds may be slowed as they flow across the earth’s surface. Very rough areas, such as suburban or heavily forested areas, can decrease wind speeds, while open terrain can increase wind speeds. The model includes estimates of the surface roughness of the topography surrounding a building, which can vary from smooth (adjacent to a large body of water) to rough (near mountains and hills). 

The calculation of property-specific Wind Factors 

A property's Wind Factor™ is an indicator of its risk of extreme wind exposure over the next thirty years.  The model assigns each property a Wind Factor, ranging from 1 (minimal risk) to 10 (extreme risk). For every location, the likely exposure to extreme wind is calculated for today and 30 years into the future and takes into account the local conditions such as the roughness of the landscape surrounding a property. A property’s Wind Factor is based on that 30-year estimate, which means that a property with a higher Wind Factor currently has a higher likelihood to experience higher winds more frequently today and in the future than a property with a lower Wind Factor score. Learn more.

Calculating the cost of wind

The amount of damage a building experiences from hurricanes, tornadoes, or other severe wind events, depends on many factors including the buildings’ characteristics such as the building height and the roof material, whether it's in an area at risk of man-made debris, the direction the building faces, and the direction of the wind gusts. The wind damage varies based on the predominant angle between the oncoming wind and the orientation of the building and rooftop.

To understand the potential damages, First Street Foundation partnered with the global engineering firm Arup. Arup simulated the impact of hundreds of different hurricane scenarios using a virtual model of the building to estimate the extent and severity of hurricane damage on individual buildings. This is then translated to financial loss and downtime.

Given the likelihood of wind events and estimates of their severity, the probable damages that will be incurred by a structure may be estimated by engineering professionals. In conjunction with Arup, a global engineering firm that specializes in structural engineering and damage estimates, First Street has developed an estimate of the average annual loss (AAL) for every building impacted by extreme winds - the AAL is the average cost of damage a home could expect, in average over many years on a per-year basis.  While hurricane strength is usually categorized by the sustained 1-minute duration wind speeds within the storm, the most extreme damages to a structure are usually caused by the 3-second duration gusts that are a result of small-scale vortices and fluctuations in wind speeds. These gusts impart the greatest stress on the building, and their magnitude is estimated statistically from the sustained wind speed, and the magnitude of those gusts is used to estimate the AAL.

The angle that the winds hit the structure also can also impact the drag and stress on the roofs, walls, and windows of a structure. The angle between the most likely wind direction and the longest face of each structure is used to determine the estimated damages.  The First Street Foundation’s Wind Model combines open-source and 3rd party data on building characteristics and location to include a calculation of the AAL for each home over a 30-year period.

Ensuring scientific accuracy

The First Street Foundation Wind Model brought together top climate scientists, modelers, engineers, technologists, and analysts. Results of the model have been computed for the US, and compared against historical hurricane wind damage data, and historical hurricane records. Using Open Science protocols, all methods used by the First Street Foundation Wind Model have been submitted to scientific peer-review journals and are also available to read on the First Street Foundation website.

Continuously improving over time

First Street Foundation has made its wind model’s full technical methodology available to the public because it supports Open Science with scientific collaboration and data transparency to help instill trust in the model results. The First Street Foundation Wind Model will continue to incorporate feedback and improve its model over time, including annual data updates as new data become available.

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