Canadian Humidity Index (HUMIDEX)

`HDX = f(DBT,DEW)`

`(DBT)"Dry Bulb Temperature"`

`(DEW)"Dew Point Temperature"`

The Math / Science

The humidex (short for humidity index) is an index number used by Canadian meteorologists to describe how hot the weather feels to the average person, by combining the effect of heat and humidity. The humidex is a dimensionless quantity based on the dew point. It is not equivalent to a dry temperature in degrees Celsius, it is just calculated to look like it.⁽¹⁾ Don't know the dew point? No problem, you can calculate it using the conversion from Relative Humidity.

Dry bulb temperature (DBT) is the temperature of air measured by a standard thermometer, which is not influenced by the humidity of the air. It is one of the fundamental parameters in the field of thermodynamics and meteorology, used to describe the state of the air in terms of its temperature alone. DBT is measured using a thermometer exposed to the air but shielded from direct radiation and moisture. This ensures the reading reflects the true air temperature without interference from external sources. The instrument used can be a simple mercury thermometer or more sophisticated electronic sensors.

Dew point temperature (DEW) is the temperature at which air becomes saturated with moisture and water vapor begins to condense into liquid water. It represents the point at which the air cannot hold any more water vapor without it condensing out. This concept is fundamental in understanding humidity, condensation, and various weather phenomena. The dew point is closely related to relative humidity (RH). When the dew point is close to the current air temperature, the RH is high, indicating moist air. When the dew point is far below the air temperature, the RH is low, indicating dry air.

Range of humidex: Degree of comfort⁽²⁾

Less than 29: No discomfort
30 to 39: Some discomfort
40 to 45: Great discomfort; avoid exertion
Above 45: Dangerous; Heat stroke possible

HUMIDEX Equation

The formula for Humidex in this calculator is:

HDX = DBT + 0.5555 { 6.11 x exp[ 5417.7530 ( 1/273.15 - 1 / (273.15 + DEW) ) ] -10 }

Where

Humidex (HDX) is the Canadian Humidity Index
DBT is the dry ambient temperature in °C.
DEW is the dew point temperature in °C.

The Humidex is designed to represent human heat stress conditions and is not meaningful at cool temperatures.⁽⁴⁾

Weather (Meteorology) Calculators

Heat Index: Approximates the heat index based on the temperature and relative humidity
Canadian Humidity Index (HUMIDEX): Computes the Canadian Humidity Index (HUMIDEX) based on the dry-bulb ambient temperature and the dew-point temperature.
Australian Apparent Temperature (AT): Computes the apparent temperature based on the dry ambient temperature, the relative humidity and the wind speed at ten meters.
Relative Humidity: Computes the relative humidity based on the actual density of vapor and the saturated density.
Dew Point from Relative Humidity: Computes the dew point based on the relative humidity and ambient temperature.
Summer Simmer Index: Computes the Summer Simmer Index based on the air temperature and relative humidity.
Wind Chill Index (North America): Computes the wind chill index based on the air temperature and the velocity of the wind.
Wet-Bulb Globe Temperature (WBGT): Computes the wet-bulb globe temperature index based on dry-bulb (air) temperature, globe thermometer temperature and the wet-bulb temperature.
Humature Index: Estimates the humidity index based on the temperature and dew point.
Antoine Equation: Computes the apparent vapor pressure of pure substances based on temperature and coefficients for the substance.
Barometric Formula (Tropospheric) calculator computes the normal barometric pressure based on the altitude (h) using the Exponential Atmosphere formula.
Planetary Temperature: Estimates a planet's temperature based on the luminosity of its star, distance to the star, average albedo and infrared optical depth of atmosphere.
Snow Water Equivalent (SWE): Computes the volume of liquid water contained in rain or snow pack defined by area, depth and snow type or rain.

References

Humidex. (n.d.). Retrieved May 19, 2016, from https://en.wikipedia.org/wiki/Humidex
Weather and Meteorology. (n.d.). Retrieved May 19, 2016, from http://ec.gc.ca/meteo-weather/default.asp?lang=En
Masterton JM, Richardson FA (1979) A method of quantifying human discomfort due to excessive heat and humidity. Downsview, Ontario, Canada:AES, Env. Canada, CLI 1-79.
Smoyer-Tomic, K. E., & Rainham, D. G. (2001). Beating the heat: development and evaluation of a Canadian hot weather health-response plan. Environmental health perspectives, 109(12), 1241.