UTCI (Universal Thermal Climate Index)
The Universal Thermal Climatic Index UTCI allows an evaluation of outdoor thermal conditions based on the dynamic physiological response of the organism calculated with a model of human thermoregulation (Fiala model). The Fiala model is thereby coupled with a "state-of-the-art" clothing model.
The UTCI follows the concept of an equivalent temperature (like PET). This means that for any combination of air temperature, wind speed, mean radiant temperature, and water vapor pressure (humidity), the UTCI is defined as the air temperature under reference conditions at which the dynamic stimulus response of the organism, the physiological stress, is equal to that under the conditions currently under consideration. The reference environment was defined with a relative humidity of 50% (up to a maximum water vapor pressure of 20 hPa), no wind, and mean radiant temperature equal to air temperature. These dynamic physiological responses are multidimensional (core temperature, sweat rate, skin moisture, etc. at different exposure times). Therefore, as a one-dimensional representation of the model responses, the UTCI was calculated as a stress index via a principal component analysis. Thermal stress can thus be assessed using a 10-point scale from "extreme heat stress" to "extreme cold stress." The operational procedure can be downloaded free of charge from the UTCI-Website. UTCI is an international assessment standard (COST Action 730, WMO Commission on Climatology CCL) based on scientific advances over the past four decades in modeling thermoregulation, including the acclimatization problem. The term "universal" is intended to illustrate that the UTCI is appropriate for all issues of physiologically relevant outdoor thermal environmental assessment in the major fields of human biometeorology: forecasting and warning, bioclimate mapping, urban and regional planning, environmental epidemiology, and climate impact research. The UTCI is valid in all climates, seasons and at all scales.