CONICET | Buscador de Institutos y Recursos Humanos

Outdoor human comfort is an essential factor to quantify the perceived quality of the urban microclimate, and taking this dimension into account already in the design phase can lead to a more holistic view of sustainable urban development. Specially, in arid regions, high outdoor air temperatures due to intensive solar radiation and low relative humidity are present in hot summer seasons. Consequently, discomfort sensations and heat stress are expected. It is currently estimated that approximately one third of the world population lives in cities located in regions classified as extremely arid, arid or semi-arid.Since the beginning of the 20th century, human thermal comfort under indoor conditions and outdoor conditions have been discussed exhaustively in several reports. More than 100 simple thermal indices, mostly two parameter indices, have been developed in the last 150 years in order to describe the complex conditions of heat exchange between the human body and its thermal environment. However, the existing works are characterized by a certain variety of instruments and methods. An example can be found in the indices and evaluation scales used to estimate thermal perception. Therefore, this paper is a continuation of a previous work and proposes the comparison of six thermal comfort indices and its contrast with subjective answers in winter, summer and annual. The goal is identifying which of them can be better used to predict thermal comfort in forested outdoor spaces of the Mendoza Metropolitan Area (MMA), an ?oasis city?. It is the fifth largest city in the country, with a population of 1,055,679, and covers 168 km2. According to the Köppen?Greiger classification, the climate of the city is arid: BWh or BWk depending on the isotherm.For this purpose, air temperature, solar radiation, relative humidity and wind speed of two meteorological stations in the downtown of MMA during winter of 2010 and summer of 2011 were selected for comparison. From the methodological point of view, it is important to note that the study of thermal comfort in MMA differs greatly from other regions, since the city is located in an arid zone with an extensive urban forest and has large daily and seasonal thermal amplitudes. While the microclimatic monitoring was being carried out, people were also studied in their natural environment, through observation and structured interviews, in order to evaluate comfort levels and perception of the environment. The first part of the questionnaire consisted of items related to sex, age, clothing, and activity done before the interview and where they were coming from (to account for acclimatization). The second part addressed the perception of the thermal sensation on a 5-point scale, ranging from -2 (very cold) to +2 (very hot), going through zero (neutral), which has been defined as the Actual Sensation Vote, or ASV.The results showed that the indices had variated correlations with subjective in both seasons. The UTCI reported an annual percentage of correct predictions of 48.8%, higher than the PMV (38.1%), COMFA (23.8%), GOCI (13.1%) and PET (3.6%) but lower than the IZA (78.6%). The higher predictive ability of this last index is due to the fact that it was specifically meant for the MMA?s population. Finally, these tools are very useful in the design and evaluation of the thermal behaviour of open spaces according not only to climate criteria but also to the subjective characteristics of users.