Analysis of UTCI in the Czech Republic: a comparison of two reanalyses

The universal thermal climate index (UTCI) is a widely used index evaluating stress caused by meteorological conditions on humans. The index combines the four meteorological elements: temperature, humidity, wind speed, and mean radiant temperature. The UTCI index can be gained from observed data, however, its calculation is also incorporated in several reanalyses. Here, the comparison of the index for the Czech Republic is made between two reanalyses, that is, the ERA5 and Aladin reanalyses. The ERA5 reanalysis is a global dataset produced in a much coarser resolution (approximately 27 km), whereas the Aladin reanalysis is adjusted for the Czech Republic with the finer resolution of 2.7 km. Hence, we analyze and compare both datasets between 1989 and 2020 for the Czech Republic. Firstly, both reanalyses are interpolated on the same grid with a 7.1 km grid step. Subsequent comparison reveals a large similarity between both reanalyses, probably due to the fact that ERA5 is a control dataset for the Aladin reanalysis. The general climatology of UTCI for the Czech Republic is presented in both reanalyses. Furthermore, trends of UTCI over the 30year period are calculated for the whole country as well as for selected interesting sites. A detailed examination is given to the differences between eastern and western parts of the country to evaluate impact of the rising continentality of climate toward east. The dependence of UTCI on altitude in both reanalyses is determined as well. Finally, trends between rural and urban areas are compared to asses trends of UTCI in urban heat islands. The results of this work will be used in the future for bioclimatological mapping of the Czech Republic.