Bodźcowość warunków biometeorologicznych we Wrocławiu
Stimulating qualities of biometeorological conditions in Wrocław

Summary/Abstract: In this paper, the values of the Universal Thermal Climate Index (UTCI) in Wrocław-Swojczycefrom recent years (2008–2014) were analyzed, calculated from 1-hour data with the use of measuredcomponents of solar radiation balance. The aim of the study was an analysis of the annual course ofUTCI in Wrocław-Swojczyce and the occurrence frequency of UTCI levels corresponding to a specificstimulating condition (heat and cold stress) as well as emphasizing the dependence of its occurrencewith specified meteorological determinants. The values of UTCI were calculated according to methodology described by Błażejczyk at al. (2010) on the basis of meteorological data from the Agro- and Hydrometeorological Observatory of Wrocław University of Environmental and Life Science. The influence of meteorological conditionson the extreme values of UTCI forming was evaluated for selected periods of cold and heat-waves. To evaluate the influence of air circulation determinants on UTCI values, circulation types were used,classified for each day of the analyzed period according to the rules of automatic air circulation typesclassification for the Lower Silesia region (Ojrzyńska 2015). The analysis of the occurrence frequency of specific UTCI levels in Wrocław-Swojczyce confirmedthat biometeorological conditions of this place are characterized by significant (40%) occurrenceof heat load deficiency (26 > UTCI> 9). The highest frequency values of this UTCI level werenoted for the summer months. In the analyzed years the occurrence of stimulating levels of UTCI was noted, but more often the loads were connected with cold stress. The most frequent moderate coldstress was noted from December to March. It was proved that for Wrocław-Swojec this characteristicis low, not exceeding 6% frequency of the occurrence of moderate heat stress (32 > UTCI > 26) andclose to 1% of mean frequency of strong heat stress (38 > UTCI > 32).The most stimulating conditions – extreme levels of UTCI – were most often noted in situationswith indefinite direction of advection and during advection from south to east. Strong heat stress wasoften observed in anticyclone situations in wet air masses. The strongest cold stress appeared in anticyclone,in dry air masses and in situations with advection of cold air from north in the upper part ofthe troposphere (upper cyclone). In cyclone with a high dynamic of wind, moderate cold stress (13 >UTCI > 0) and less often strong cold stress (–27 > UTCI > –13) was mainly observed, however theincrease of its occurrence frequency in the years 2011–2013 contributed to the increase in the generalfrequency occurence of cold stress in Wrocław-Swojczyce.In the described anticyclonic situation during the heat wave, the course of the UTCI value waslevelized and clearly corresponded with solar factors which form the air temperature T and the meanradiant temperature Mrt. In the cold – wave period, in cyclonic situation, the smallest decrease of theUTCI values was noted for high wind speed and in cases of low values of water vapour pressure. Theinfluence of these meteorological factors on the UTCI values was so strong, that it caused significantvariation and obliteration of the general UTCI course connected with the solar determinant. The studyproved that the lack of information about the components of the solar radiation balance in UTCI calculationsleads underestimation in the UTCI, averagely about 2,7°C.

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