Thermal comfort in Quebec City, Canada: sensitivity analysis of the UTCI and other popular thermal comfort indices in a mid-latitude continental city

Abstract

The newly developed Universal Thermal Climate Index (UTCI), along with the physiological equivalent temperature (PET), the humidex (HX) and the wind chill index (WC), was calculated in Quebec City, Canada, a city with a strong seasonal climatic variability, over a 1-year period. The objective of this study is twofold: evaluate the operational benefits of implementing the UTCI for a climate monitoring program of public comfort and health awareness as opposed to relying on traditional and simple indices, and determine whether thermal comfort monitoring specific to dense urban neighborhoods is necessary to adequately fulfill the goals of the program. In order to do so, an analysis is performed to evaluate each of these indices' sensitivity to the meteorological variables that regulate them in different environments. Overall, the UTCI was found to be slightly more sensitive to mean radiant temperature, moderately more sensitive to humidity and much more sensitive to wind speed than the PET. This dynamic changed slightly depending on the environment and the season. In hot weather, the PET was found to be more sensitive to mean radiant temperature and therefore reached high values that could potentially be hazardous more frequently than the UTCI and the HX. In turn, the UTCI's stronger sensitivity to wind speed makes it a superior index to identify potentially hazardous weather in winter compared to the PET and the WC. Adopting the UTCI broadly would be an improvement over the traditionally popular HX and WC indices. The urban environment produced favorable conditions to sustain heat stress conditions, where the indices reached high values more frequently there than in suburban locations, which advocates for weather monitoring specific to denser urban areas.

Investigating the Behaviour of Human Thermal Indices under Divergent Atmospheric Conditions: A Sensitivity Analysis Approach

“…Only the UTCI index fluctuates considerably under T a Class1 and Class2 conditions, having the highest sensitivity among the selected indices. The above findings are in agreement with the results of Charalampopoulos [27] and Provençal et al [106] which confirm the low sensitivity to WS and the comparatively higher sensitivity of UTCI. Additionally, it was found that as T a increases, the UTCI sensitivity lowered, and under hot conditions (Class 4, 30 • C < T a ≤ 45 • C) the UTCI presented lower mean sensitivity in comparison to the cases of PET's and mPET's.…”

“…The gradient of the sensitivity patterns accompanied by the summary statistics proves that VP has a weak influence on 'G' category indices' fluctuation. This finding is in agreement with the results of [27], but when examining the comparative indices' sensitivity, those results are partially in contrary with the results of [106] since they found that the UTCI is less sensitive than PET and mPET. According to analysis undertaken by this study, the UTCI is more sensitive than PET and mPET under lower VP environments, but less so for conditions with high VP values.…”

“…Since the sensitivity of the indices to WS variation and change rate under different GR classes were examined, it was required to interpret the findings of previous studies that focused on both atmospheric parameters. As a result, the pinpointed distinct behaviour of UTCI to WS variation is corroborated by adjacent studies, including [27,77,106]. In addition, the GR results confirm the findings of Provençal et al [106] regarding the higher sensitivity of PET, and the findings of Charalampopoulos [27] for the UTCI's sensitivity patterns to variation and change rates of radiation fluxes in urban environments.…”

“…As a result, the pinpointed distinct behaviour of UTCI to WS variation is corroborated by adjacent studies, including [27,77,106]. In addition, the GR results confirm the findings of Provençal et al [106] regarding the higher sensitivity of PET, and the findings of Charalampopoulos [27] for the UTCI's sensitivity patterns to variation and change rates of radiation fluxes in urban environments. For this reason, the analysis of the results strengthen the identified high sensitivity of the UTCI to WS variation (and change rate) under low GR conditions and the superior sensitivity of PET and mPET under sunny conditions.…”

“…The 'C' category (the algebraic indices) presented a very low sensitivity, in comparison to the rest of the indices, no matter the GR and T a class, nor the variation and change rate of the WS, VP and T a parameters. This behaviour was partly expected when taking into account the input parameters, the equations of the related indices, and the outcomes of previously published studies in this field [27,41,59,106,107]. The next group contains the PET, mPET and PT indices, which presented similar qualitative and quantitative behaviour under all classes and conditions.…”