Sensitivity of UTCI Thermal Comfort Prediction to Personal and Situational Factors—Residual Analysis of Pedestrian Survey Data

Abstract

The Universal Thermal Climate Index (UTCI) assesses the interaction of ambient temperature, wind, humidity and radiant fluxes on human physiology in outdoor environments on an equivalent temperature scale. Based upon the dynamic thermal sensation (DTS) from the UTCI-Fiala model of human thermoregulation, the UTCI allows for thermal comfort prediction.Here we compare those predictions to thermal sensation votes as recorded on the 7-unit ASHRAE scale for two Brazilian cities, Curitiba and Pelotas. Outdoor comfort surveys from 1551 respondents in Curitiba and 1148 in Pelotas, respectively, yielded negligible bias and less than one unit rootmean square error (rmse), which was similar in magnitude for both study areas. Residual analysis revealed that factors such as age, sex, body composition, site morphology (open space, street canyon), climatic state (comfort/discomfort) and clothing choice only explained a small portion of the prediction error variance, which in the total sample was dominated for over 94% by residual inter-individual variability. Adding historical weather information from the previous three days gave superior information compared to longer time lags and helped to reduce the residual variance to 88%. Those findings underpin current limitations in individual thermal comfort prediction, whereas personal and situational factors hardly affected 2 UTCI predictive performance, which showed reasonable accuracy at the population level.

Feasibility of climate reanalysis data as a proxy for onsite weather measurements in outdoor thermal comfort surveys

“…UTCI reanalysis data as provided by ERA5-HEAT have recently been explored in the context of OTC in urban areas. The effect of pedestrians' history on their thermal comfort, for instance, has been assessed in two different locations in southern Brazil by retrieving ERA5-HEAT UTCI at the days, weeks and months preceding OTC surveys (Bröde et al 2021). As pre-survey UTCI data are not available from portable weather stations (the latter measure outdoor environmental variables only for the period when OTC surveys are taken), ERA5-HEAT turned out as a relevant source for obtaining historical UTCI data.…”