Temporal Analysis of Urban-Suburban PET, mPET and UTCI Indices in Belgrade (Serbia)

Abstract

The analysis of the bioclimatic conditions is becoming increasingly relevant in climate interpretations for human needs, particularly in spatial planning, tourism, public health, sports events, bio-prognosis, etc. In this context, our study presents general temporal bioclimatic conditions in Belgrade, defined based on the PET, mPET and UTCI heat budget indices. Monthly, seasonal and annual indices were analyzed for urban and suburban weather stations based on 43 annual sets of meteorological data obtained by hourly observations at 7 h and 14 h CET. This study aims to present the distribution of PET, mPET and UTCI indices to show the pattern of each index in a mild climate location and to examine annual and seasonal differences of each index in the Belgrade urban center and suburban part of the city. The study results indicate higher biothermal stress in the urban area compared to the suburban zone and that the indices are congruent during the summer. At the same time, during the winter, they are more difficult to compare due to their peculiarities becoming more noticeable. The results obtained of all mean monthly and mean annual values of all three indices clearly indicate the difference that follows the definition of the urban heat island (UHI), particularly those from morning observation and winter season. The UTCI index shows the most significant monthly, seasonal and annual difference between urban and suburban areas for both observations. The annual difference of ΔUTCI7h amounts to 1.5 °C is the same as the annual difference of minimum temperatures (Δtmin). In contrast, the annual differences of ΔPET7h ΔmPET7h are °smaller (0.8 °C and 0.7 °C) and closer to the annual differences of maximum temperatures Δtmax amounted of 0.6 °C.

Assessment of Outdoor Thermal Comfort in Serbia’s Urban Environments during Different Seasons

“…These hourly values of the considered index allow us to monitor how the outdoor thermal comfort of urban zones changes throughout the day, from morning to evening, during each season. Also, as Pecelj et al pointed out in their study, these hours correspond to the most common time of occurrence of daily minimum and maximum air temperatures [52]. The results were shown by season (spring, summer, autumn and winter) and "year by year" (from 1999 to 2018).…”

“…Equally, this index represents various climates, weather, and locations excellently. The UTCI is very sensitive to outdoor factors [69], i.e., changes in air temperature, relative humidity, solar radiation, and wind speed [52]. It is one of the most comprehensive indices for the determination of heat and cold stress in the outdoor environment [70].…”

“…Physiological parameters (metabolic rate and thermal properties of clothing) are taken as universal constants in the model due to the evaluation by means of regression equation [21]. This implies an outdoor activity where an average person walks at a speed of 4 km/h (1.1 m/s), resulting in a heat production of 135 W/m 2 ( 2.3 MET) of metabolic energy [52,68] and clothing insulation, which is self-adapting according to the environmental conditions [52,75]. It is important to emphasize that clothing insulation, vapor resistance and the insulation of surface air layers are highly affected by changes in wind speed and body movement, which will influence physiological responses [52,69].…”

“…An integral part of this software package is the model used to determine Tmrt, based on the available data-in this case that were cloudiness (cloud cover, N) and the height of the Sun (Sun altitude, hSl) [76]. Also, some of the authors believe that for the purposes of bioclimatic research in urban areas, it is more relevant to use indices that include wind speed at a height of 1.1 m above the surface (which is equivalent to a standing person's body center) or combine them together with the UTCI [52], as opposed to wind speed at a height of 10 m above the ground, which is the case when we use UTCI [76].…”

“…In recent years urban OTC, the application of UTCI, and other thermal indices have become the subjects of many scientific studies by numerous researchers from Serbia and other Western Balkan countries [21,22,25,[46][47][48][49][50][51]. Regarding the application of UTCI in studies of Serbian urban bioclimate, this index was analyzed, e.g., by Pecelj et al in order to compare bioclimatic conditions in the urban and suburban zones of Belgrade [52]. Belgrade's urban climate in relation to HL and UTCI was once again examined when Pecelj et al [53] examined biothermal conditions in different geographical environments in Serbia.…”