Heat Factor Terminology

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Understand the meaning of commonly used terms on Heat Factor.

Heat Risk Overview

First Street Foundation Extreme Heat Model (FSF-EHM): First Street Foundation's heat methodology and  Extreme Heat Model is a spatial temperature model that determines the exposure of a specific location to extreme heat. Exposure to extreme heat considers how the temperature of a specific location is affected by its immediate surroundings. Heat Factors are derived from this model and 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 is expected to grow over the next 30 years.   

Hot day: The term “hot day” is used to represent local heat index temperatures or temperatures that would be seen only about 2% of days each year by the heat index. The FSF-EHM uses data from the Climate Model Intercomparison Project to identify the temperature on the hottest 7 days in a given area and uses that to define what some in the area would call a “hot day”.

Energy Usage

Estimated yearly cooling days: Estimated number of days each year when air conditioning would be recommended to maintain a comfortable indoor temperature. The number of cooling days is the difference between the daily average temperature and 70°F. Estimated yearly cooling days refer to the number of days in a given year when the temperature is warmer than 70°F and therefore requires the use of air conditioning to maintain a comfortable indoor temperature. It's important to note that cooling days on Risk Factor only consider air conditioning, not other cooling devices such as fans.

Estimated yearly energy consumption: The estimated amount of energy required to cool a home in a given year. The amount of energy required to cool a home depends on the number of cooling days estimated for a property, the degrees of cooling required to maintain a consistent indoor temperature, and specific property characteristics such as the number of bedrooms, the age of the home, and square footage. 

Estimated yearly energy costs for cooling in dollars: The price each household will pay for electricity varies depending on where the local grid is supplied, the companies that supply an area, and the 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.

Heat Trends

Average daily maximum temperature: The 30-day average of the daily high temperatures for the hottest month of the year.

Dangerous days:  Days with temperatures above 100°F. Although slightly lower, this threshold temperature is informed by the National Weather Service which considers temperatures above 103°F to be dangerous days. When temperatures are above 100°F, early-stage heat-related illnesses such as cramps and heat exhaustion go from being possible to be likely for anyone who is exposed to heat for a prolonged period of time. 

Health caution days: The National Weather Service identifies days of “Extreme Caution” to be temperatures above 90°F.  At these temperatures heat stroke, cramps, and heat exhaustion become possible from extended exposure to extreme heat, particularly for vulnerable populations. 

Heatwave: Any event where the temperature meets or exceeds the local definition of a “hot day” for more than one consecutive day.

Heatwave likelihood: The likelihood that any 3+ day stretch of temperatures is above the local “hot day” temperature.

Heat wavelength: The number of days in a row the temperature is expected to be higher than the local definition of a “hot day”.  The number of consecutive days the temperature is expected to be higher than the local “hot day”.

Environmental Changes

Heat index: Refers to the “feels like” temperature, or what the temperature outside feels like when relative humidity is combined with air temperature. Heat index is defined by the National Weather Service as a measure of how hot it really feels when relative humidity is factored in with the actual air temperature

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