The appraisal of climate trends in the Ukrainian Roztochya on the basis of pluviothermal conditions

Abstract

The Roztochya Nature Reserve is located in the Roztochya physical and geographical region which is a part of the Main European Watershed and is located in the border areas of Ukraine and Poland. Köppen-Geiger climate type – Dfb. Within the area of the reserve, there is its own weather station ( 49°55'N 23°45'E). The data on meteorological observations obtained here in the period 2005-2020 were compared with long-term archival data for the first half of the twentieth century according to the Rava-Ruska weather station (northern part of the Ukrainian Roztochya – 50°14´N 23°37´E) and data from the Steppe zone of Ukraine and Southern Europe. The object of research was the meteorological data obtained at the weather station of the Roztochya Nature Reserve for the period 2005-2020, namely: monthly average, maximum, minimum air temperatures, the sums of physiological active temperatures, the monthly amount of atmospheric precipitation; the average annual air temperatures and the amount of annual precipitation, as well as the sum of average monthly temperatures and precipitation by calendar seasons of the year. The subject of the studies was local climate change in the region of Ukrainian Roztochya, based on the meteorological data. The aim of the study was to analyse the pluviothermal conditions (relationship between air temperatures and the amount of precipitation) in the region of research for the period 2005-2020. The data analysis showed the changes of the main climatic factors in the Ukrainian Roztochya region. During the study period, the average annual temperature increased by 2.2°C, and in the last five years (2016-2020) – by 3.2°C. The maximum increase took place in the winter season: in the period 2005-2020 by 2.4°С, and in the 2016-2020 period – by 3.4°С. The amounts of summer active temperatures (more than 10°С) in summer for the period 2005-2020 increased by 15%, and for the 2016-2020 period – by 18%. In dry years (2015, 2017 and 2019), these figures for the entire growing season increased by 27-36%. The amount of total annual rainfall did not decrease, but was redistributed according to the calendar seasons of the year. During the full research period, the amount of summer precipitation decreased from 40.4% to 33.2% compared to archival data, and in the last five years it amounted to only 29.8% of the annual amount. The decrease in summer precipitation in the dry years of 2015, 2017, and 2019 was especially noticeable - by 99, 182 and 105 mm, respectively. The decrease in the Sielianinov hydrothermal coefficient for the summer months of the 2005-2020 period, compared to the archival data, was 26%, and for some summer months of 2015, 2017, and 2019, this figure ranged from the minimum decadal values of 0.01 to average monthly values from 0.1 to 0.9. According to the method of this author, such periods are defined as "very severe drought", "severe drought" and "moderate drought". Over the last decade, Wilhelm's border of drought for Ukraine and de Martonne's aridity index differ from archival data by 14%; and the Lang's rainfall factor differs by 31%. The driest and warmest year 2019 in terms of annual temperature and precipitation by the rain factor according to Lang almost approached Florence; and in terms of de Martonne’s aridity index, this is only 15% less than Mariupol, and only 9% less than Avignon. An analysis of the graphical representation of temperatures and precipitation (climographs) showed the main trends in the balance of heat and moisture during the year – there was not only a decrease in summer precipitation, but also a shift in their peak from July to May. Therefore, the sum of active temperatures provided by moisture in natural conditions is actually much lower than the total amount of active temperatures. Plants cannot get enough moisture and this adversely affects all vegetative processes. The climographs of abnormally dry years 2015, 2017, and 2019 in the Ukrainian Roztochya resemble the Mediterranean type of climate with a deficit of moisture in the warm season (when the summer temperature maximum is superimposed on the precipitation minimum). It is clear that at the moment it is too early to speak about the regional consequences of significant climate change, but further increase in temperatures and a decrease in the amount of precipitation during the active growing season will lead to significant changes in the hydrological regime. Rare and endangered species, as well as native species on the border of the area, will be especially vulnerable in such conditions.

Keywords

• roztochya nature reserve
• weather station
• meteorological data
• climate types
• temperatures and precipitation
• climographs
• climate changes
• anomalous climate years