Variations in relative humidity across Poland and its possible impacts on outdoor thermal comfort: An analysis based on hourly data from 1995 to 2020

Abstract

AbstractThis study investigated the variations in relative humidity (RH) and its impacts on outdoor thermal comfort in Poland. The study considered hourly RH data from 44 stations over the period 1995–2020. A countrywide declining trend in average RH was seen over the above period. This trend was more pronounced at stations in central and northwestern Poland. In the majority of the stations, in spring and summer, a statistically significant decline in the average RH was seen in the period 2008–2020 (second half of data) in comparison to that in the period 1995–2007 (first half of data). In all seasons, during the period 1995–2020, frequency distributions of RH corresponding to all stations were heavily left‐skewed and the peak occurred at an RH around about 90–95% or even higher. This indicated that high RH values are frequent in Poland. In the majority of the stations, an increase in the average number of hours per year above high percentiles of RH (95, 96th, 97th, 98th, 99th and 99.5th) and an increase in the average number of hours per year below low percentiles of RH (0.5th, 1st, 2nd, 3rd, 4th and 5th) were seen in the period 2008–2020 compared to that in the period 1995–2007. The above findings lead to the conclusion that occurrences of low and high extremes of RH have increased though the average of RH shows a decline. Also, in the majority of the stations, the number of hot–humid hours and the number of cold–dry hours have increased in the period 2008–2020 compared to those in the period 1995–2007. According to the Discomfort Index, over the period 1995–2020, the outdoor warm thermal comfort in Poland has declined due to high temperature and high humidity.