The assessment of the thermophysiological effects of the atmospheric environment is one of the key issues in human biometeorology. Numerous thermal indices have been published to-date, however only a few of them have had limited operational utilisation in certain geographical regions. Based on current scientific progress, and with increased international travel and easy access to information, there is a need for global harmonisation of the development and dissemination of various weather and climatic indices. Therefore, ISB has established Commission 6 with the task to review the past 30 years of scientific progress and to integrate new knowledge and concerns into a Universal Thermal Climate Index (UTCI) for assessments of the outdoor thermal environment.

The UTCI will be a state-of-the-art index, taking into account all significant heat exchange mechanisms. Input variables include air temperature, water vapour pressure, wind velocity, short- and long-wave radiant fluxes, in addition to metabolic rate and clothing insulation. UTCI will satisfy the following basic requirements: a) thermophysiologically valid (significant in the whole range of heat exchange); b) applicable in all climates; c) independent of individual (personal) characteristics.

When fully developed, UTCI will be:

- based on the most advanced multi-node thermophysiological models;

- capable of predicting whole body thermal effects (hypothermia and hyperthermia; warm and cold discomfort), and local effects (facial, hands and feet cooling and frostbite);

- linked to an expert system (e.g. look-up tables, parameterisation by regression).

UTCI will be a temperature scale index, (i.e. the air temperature of a defined reference environment providing the same thermal strain on human beings as the actual environment). It can be used in daily weather forecasts to advise the public of levels of discomfort due to heat and cold, and in warnings of the danger of thermal extremes especially to vulnerable groups. It can also be a useful tool in bioclimate assessments (mapping in all scales, engineering applications), epidemiology (morbidity and mortality studies), and climate impact research (e.g. climate change studies).

This presentation will review progress to-date of ISB Commission 6 in developing UTCI, including comparisons between simulations based on multi-node and existing advanced models.