UTCI - why another thermal index?

Existing procedures for the assessment of the thermal environment in the fields of public weather services, public health systems, precautionary planning, urban design, tourism and recreation and climate impact research exhibit significant shortcomings. This is most evident for simple (mostly two-parameter) indices, when comparing them to complete heat budget models developed since the 1960s. ISB Commission 6 took up the idea of developing a Universal Thermal Climate Index (UTCI) based on the most advanced multi-node model of thermoregulation representing progress in science within the last three to four decades, both in thermophysiological and heat exchange theory. Creating the essential research synergies for the development of UTCI required pooling the resources of multidisciplinary experts in the fields of thermal physiology, mathematical modelling, occupational medicine, meteorological data handling (in particular radiation modelling) and application development in a network. It was possible to extend the expertise of ISB Commission 6 substantially by COST (a European programme promoting Cooperation in Science and Technology) Action 730 so that finally over 45 scientists from 23 countries (Australia, Canada, Israel, several Europe countries, New Zealand, and the United States) worked together. The work was performed under the umbrella of theWMO Commission on Climatology (CCl). After extensive evaluations, Fiala’s multi-node human physiology and thermal comfort model (FPC) was adopted for this study. The model was validated extensively, applying as yet unused data from other research groups, and extended for the purposes of the project. This model was coupled with a state-of-the-art clothing model taking into consideration behavioural adaptation of clothing insulation by the general urban population in response to actual environmental temperature. UTCI was then derived conceptually as an equivalent temperature (ET). Thus, for any combination of air temperature, wind, radiation, and humidity (stress), UTCI is defined as the isothermal air temperature of the reference condition that would elicit the same dynamic response (strain) of the physiological model. As UTCI is based on contemporary science its use will standardise applications in the major fields of human biometeorology, thus making research results comparable and physiologically relevant

The Universal Thermal Climate Index UTCI in operational use

The Universal Thermal Climate Index UTCI provides an assessment of the outdoor thermal environment in bio-meteorological applications based on the equivalence of the dynamic physiological response predicted by a model of human thermoregulation, which was coupled with a state-of-the-art clothing model. The operational procedure, which is available as software from the UTCI website (www.utci.org), showed plausible responses to the influence of humidity and heat radiation in the heat, as well as to wind speed in the cold and was in good agreement with the assessment of ergonomics standards concerned with the thermal environment. This suggests that in this regard UTCI may be universally useable in the research and in the major areas of application of human biometeorology

UTCI-Fiala multi-node model of human heat transfer and temperature regulation.

The UTCI-Fiala mathematical model of human temperature regulation forms the basis of the new Universal Thermal Climate Index (UTC). Following extensive validation tests, adaptations and extensions, such as the inclusion of an adaptive clothing model, the model was used to predict human temperature and regulatory responses for combinations of the prevailing outdoor climate conditions. This paper provides an overview of the underlying algorithms and methods that constitute the multi-node dynamic UTCI-Fiala model of human thermal physiology and comfort. Treated topics include modelling heat and mass transfer within the body, numerical techniques, modelling environmental heat exchanges, thermoregulatory reactions of the central nervous system, and perceptual responses. Other contributions of this special issue describe the validation of the UTCI-Fiala model against measured data and the development of the adaptive clothing model for outdoor climates

Validation of the Fiala multi-node thermophysiological model for UTCI application

The important requirement that COST Action 730 demanded of the physiological model to be used for the Universal Thermal Climate Index (UTCI) was its capability of accurate simulation of human thermophysiological responses across a wide range of relevant environmental conditions, such as conditions corresponding to the selection of all habitable climates and their seasonal changes, and transient conditions representing the temporal variation of outdoor conditions. In the first part of this study, available heat budget/two-node models and multi-node thermophysiological models were evaluated by direct comparison over a wide spectrum of climatic conditions. The UTCI-Fiala model predicted most reliably the average human thermal response, as shown by least deviations from physiologically plausible responses when compared to other models. In the second part of the study, this model was subjected to extensive validation using the results of human subject experiments for a range of relevant (steady-state and transient) environmental conditions. The UTCI-Fiala multi-node model proved its ability to predict adequately the human physiological response for a variety of moderate and extreme conditions represented in the COST 730 database. The mean skin and core temperatures were predicted with average root-mean-square deviations of 1.35 ± 1.00°C and 0.32 ± 0.20°C, respectivel

Deriving the operational procedure for the Universal Thermal Climate Index (UTCI)

The Universal Thermal Climate Index (UTCI) aimed for a one-dimensional quantity adequately reflecting the human physiological reaction to the multi-dimensionally defined actual outdoor thermal environment. The human reaction was simulated by the UTCI-Fiala multi-node model of human thermoregulation, which was integrated with an adaptive clothing model. Following the concept of an equivalent temperature, UTCI for a given combination of wind speed, radiation, humidity and air temperature was defined as the air temperature of the reference environment, which according to the model produces an equivalent dynamic physiological response. Operationalising this concept involved (1) the definition of a reference environment with 50% relative humidity (but vapour pressure capped at 20 hPa), with calm air and radiant temperature equalling air temperature and (2) the development of a one-dimensional representation of the multivariate model output at different exposure times. The latter was achieved by principal component analyses showing that the linear combination of 7 parameters of thermophysiological strain (core, mean and facial skin temperatures, sweat production, skin wettedness, skin blood flow, shivering) after 30 and 120 min exposure time accounted for two-thirds of the total variation in the multi-dimensional dynamic physiological response. The operational procedure was completed by a scale categorising UTCI equivalent temperature values in terms of thermal stress, and by providing simplified routines for fast but sufficiently accurate calculation, which included look-up tables of pre-calculated UTCI values for a grid of all relevant combinations of climate parameters and polynomial regression equations predicting UTCI over the same grid. The analyses of the sensitivity of UTCI to humidity, radiation and wind speed showed plausible reactions in the heat as well as in the cold, and indicate that UTCI may in this regard be universally useable in the major areas of research and application in human biometeorology

An introduction to the Universal Thermal Climate Index (UTCI)

The assessment of the thermal environment is one ofthe main issues in bioclimatic research, and more than 100 simple bioclimatic indices have thus far been developed to facilitate it. However, most of these indices have proved to be of limited applicability, and do not portroy the actual impacts of thermal conditions on human beings. Indices derived from human heatbalance models (one- or two-node) have been found to offer a better representation of the environmental impact in question than do simple ones. Indeed, the new generation of multi-node models for human heat balance do allow full account to be taken of heat transfer and exchange, both within the human body and between the body surface and the surrounding air layer. In this paper, it is essential background information regarding the newly-developed Universal Thermal Climate Index UTCI that is presented, this in fact deriving from the Fiala multi-node model of human heatbalance. The UTCI is defined as the air temperature (Ta) of the reference condition causing the same model response as actual conditions. UTCI was developed in 2009 by virtue of international co-operation between leading experts in the areas of human thermophysiology, physiological modelling, meteorology and climatology. The necessary research for this had been conducted within the framework of a special commission of the International Society of Biometeorology (ISB) and European COST Action 730

Validation of the Fiala multi-node thermophysiological model for UTCI application

The important requirement that COST Action 730 demanded of the physiological model to be used for the Universal Thermal Climate Index was its capability of accurate simulation of the human thermophysiological responses across a wide range of relevant environmental conditions, such as conditions corresponding to the selection of all habitable climates and their seasonal changes, and transient conditions representing temporal variation of outdoor conditions. In the first part of this study available heat budget/two-node models and multi-node thermophysiological models were evaluated by direct comparison over the wide spectrum of climatic conditions. The UTCI-Fiala model predicted most reliably the average human thermal response which was showed by least deviations from physiologically plausible responses when compared to other models. In the second part of the study, this model was, therefore, subjected to extensive validation using results of human subject experiments for a range of relevant (steady-state and transient) environmental conditions. The UTCI-Fiala multi-node model proved its ability to predict adequately the human physiological response for a variety of moderate and extreme conditions represented in the COST 730 database. The mean skin and core temperatures were predicted with average root-meansquare deviations of 1.35 ± 1.00 °C and 0.32 ± 0.20 °C, respectively

Thermische umweltbedingungen [The thermal environment]

Zusammenfassung Die Bewertung und Vorhersage der thermischen Umweltbedingungen des Menschen in einer physiologisch korrekten, wirkungsvollen und praktischen Weise stellt eines der wichtigsten Fragestellungen in der Human-Biometeorologie dar. Dies ergibt sich aus der Notwendigkeit, den Wärmehaushalt des Menschen den thermischen Umweltbedingungen anzupassen, um Gesundheit, Wohlbefinden und Leistungsfähigkeit zu gewährleisten. Ausgehend von der Wärmbilanz des Menschen wird ein Überblick über verschiedene Bewertungsansätze gegeben bis hin zur Entwicklung des „Universellen thermischen Klimaindex UTCI“ im Rahmen der COST Action 730 (2004). Ausgewählte Anwendungen sollten die Relevanz der thermischen Bewertung im Bereich Wetter/ Klima und Gesundheit verdeutlichen. Abstract One of the fundamental issues in human biometeorology is the assessment and forecast of the thermal environment in a sound, effective and practical way. This is due to the need for human beings to balance their heat budget to a state very close to his/her thermal environment in order to optimise his/her comfort, performance and health. Based on the human heat budget an overview is given on different assessment approaches up to the development of the “Universal Thermal Climate Index” within COST Action 730 (2004). Selected applications from the weather/ climate and human health field should make clear the significance of a thermal assessment

Nowy wskaznik oceny warunkow klimatoterapii uzdrowiskowej (UTCI) [New index to evaluate climate for climatotherapy (UTCI)]

W ciągu ostatnich stu lat powstało kilkadziesiąt róŜnych wskaźników oceniających oddziaływanie środowiska atmosferycznego na człowieka. Większość z nich nie ma jednak bezpośredniego odniesienia do reakcji fizjologicznych zachodzących w organizmie pod wpływem warunków termicznych otoczenia. W latach 90. ubiegłego wieku powstały tzw. wielowęzłowe (multi node) modele bilansu cieplnego człowieka, które opisują wszystkie mechanizmy gospodarki cieplnej organizmu. Na bazie jednego z tych modeli powstał nowy wskaźnik termiczny oceniający obciąŜenia cieplne człowieka (UTCI – Universal Thermal Climate Index). Artykuł przedstawia załoŜenia i podstawy interpretacji wskaźnika oraz próbę jego wykorzystania do oceny warunków klimatoterapii uzdrowiskowej