Should public health systems use simple thermohygrometric indices into urban environment?

Outdoor human heat perception is not only related to ambient temperature and humidity, as described in most direct biometeorological indices, but also to wind speed and solar radiation. Numerous biometeorological indices are used in Heat-Health Warning System and hot weather response plans to describe the discomfort conditions during the summer. This topic is of great interest because heat wave frequency and intensity is expected to increase due to climate change. The aim of this study was to compare the performance of the most frequently used direct indices in order to assess the thermal discomfort condition during the summer period (2007 - 2010) in several cities of Tuscany (Italy). In each city, one of the interlard and one of the costal plans, characterized by different climatic and geographical conditions, data from two different weather stations were collected (one in the city center and one in the suburb) in order to describe the intra-urban difference of thermal perception. Results showed a very similar trends between all direct thermohygrometric indices even if apparent temperature index seems to be more appropriate to describe the perceived thermal conditions in suburban areas where the wind speed might also be 6-7 times stronger than in the city center. According to these results, the choice and the consequent use of an appropriate thermal index appears a very important step to implement specific preventive measures for health and to set up a reliable heat warning system for the elderly and for the entire population.