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Heat Index function

Overview

Calculates apparent temperature based on ambient temperature and relative humidity. The apparent temperature is often described as how hot it feels to the human body.

Notes

The formula for the Heat Index function uses to compute heat index is

Heat Index = (-42.379 + (2.04901523 * T) + (10.14333127 * R) - (0.22475541 * TR)  - (6.83783e-3 * TT) - (5.481717e-2 * RR) + (1.22874e-3 * TTR) + (8.5282e-4 * TRR) - (1.99e-6 * TTRR))
  • T = Air temperature
  • R = Relative humidity

This index can be useful for calculating the dangers related to medical issues such as muscle cramping, dehydration, heat exhaustion, or the more serious heatstroke on hot and humid days. When relative humidity is high, it becomes increasingly difficult for the body's sweat to evaporate, leaving individuals without an effective natural way to cool off. Maps of heat advisories or warnings are often a product of reclassifying the heat index result into classes, where the higher the index value, the more likely it is to become a warning rather than just an advisory.

Parameters

ParameterDescription

Temperature Raster

A single-band raster where pixel values represent ambient air temperature.

Temperature Units

The unit of measurement associated with the input temperature raster. Available input units are degrees Celsius, Fahrenheit, and Kelvin.

Relative Humidity Raster

A single-band raster where pixel values represent relative humidity as a percentage value between 0 and 100.

Heat Index Units

The unit of measurement associated with the output raster. Available output units are degrees Celsius, Fahrenheit, and Kelvin.

References

Steadman, Robert G. "The Assessment of Sultriness. Part I: A Temperature-Humidity Index Based on Human Physiology and Clothing Science." Journal of Applied Meteorology 18.7 (1979): 861–873.

Steadman, Robert G. "The Assessment of Sultriness. Part II: Effects of Wind, Extra Radiation and Barometric Pressure on Apparent Temperature." Journal of Applied Meteorology 18.7 (1979): 874–885.

National Weather Service. "NWS Heat Index." http://www.nws.noaa.gov/om/heat/heat_index.shtml.

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