J5B.4 AN UPDATE ON THE DEVELOPMENT OF A UNIVERSAL THERMAL CLIMATE INDEX Gerd Jendritzky * , Abdel Maarouf**, Dusan Fiala***, Henning Staiger* *Deutscher Wetterdienst, Freiburg, Germany **Environment Canada, Toronto, Canada ***De Montfort University, Leicester, U.K. 1. INTRODUCTION One of the fundamental issues in human biometeorology is the assessment of the atmospheric environment in a thermophysiologically meaningful and useful way. Due to the fact that air temperature is not the only relevant variable, more than 100 simple thermal indices - most of them two- parameter indices - have been developed in the last 150 years to describe the complex conditions of heat exchange between the human body and its thermal environment. Well- known and still popular examples are the heat index and the windchill index. For excellent reviews, see Fanger (1970), Landsberg (1972), Givoni (1976), and Driscoll (1992). However, due to the simple formulation of these indices an essential requirement was never fulfilled, that is for each index value there must always be a unique thermophysiological effect, regardless of the combination of the input meteorological values. Complete heat budget models take all mechanisms of heat exchange into account, and can be considered as state-of-the-art. Input variables include air temperature, water vapour pressure, wind velocity, mean radiant temperature including solar radiation, in addition to metabolic rate and clothing insulation. Such models possess the essential attributes to be utilized operationally in most biometeorological applications in all climates, regions, seasons, and scales. This is certainly true for MEMI (Hppe, 1984,1999), and the Outdoor Apparent Temperature (Steadman, 1984, 1994). However, it would not be the case for the simple Indoor AT, which is the basis of the US Heat Index, often used in outdoor applications neglecting the addition "Indoor". Other good indices include the Standard Predictive Index of Human Response approach (Gagge et al., ______________________________ * Corresponding author address: Gerd Jendritzky, Deutscher Wetterdienst, Unit Human Biometeorology, Freiburg, Germany, +49761-2820254; e-mail: gerd.jendritzky@dwd.de 1986), and Out_SET* (Pickup and de Dear, 2000; de Dear and Pickup, 2000) which is based on Gagge’s work. Blazejczyk (1994) presented the man-environment heat exchange model MENEX, and the extensive work by Horikoshi et al. (1995, 1997) resulted in a Thermal Environmental Index. With Gagge‘s et al. (1986) improvement in the description of latent heat fluxes by the introduction of PMV*, Fanger’s (1970) approach can also be considered among the advanced heat budget models. This approach is generally the basis for the operational thermal assessment procedure Klima-Michel-model (Jendritzky et al., 1979; Jendritzky et al., 1990) of the Deutscher Wetterdienst with the outcome "perceived temperature, PT" (Staiger et al., 1997) that considers a certain degree of adaptation by various clothing. Based on current scientific progress, and with increased international travel and easy access to information, there is a need for global harmonization of the development and dissemination of various weather and climatic indices. Considering the recent successful experience with the worldwide introduction of a universal UV-index under the umbrella of WHO and WMO, the idea came up to review what has been achieved in the past 30 years in thermophysiological modeling. Consequently, ISB has established Commission 6 to integrate new knowledge and concerns into a Universal Thermal Climate Index, UTCI, for assessments of the outdoor thermal environment. 2. Basic features of UTCI The Universal Thermal Climate Index must meet the following requirements: 1) thermophysiologically significant in the whole range of heat exchange 2) valid in all climates, seasons, and scales 3) useful for key applications in human biometeorology such as: ● daily forecasts: - public weather service