Seasons’ lengths and dates of temperature transition under the climate change

Dates of mean daily temperature transitions of 0°C, 5°C, 10°C and respective season lengths are among the most necessary information for different economic sectors of any country. Recent climate changes have already affected these characteristics. Therefore, the goal of the study was to estimate possible shifts of the temperature transition dates for four meteorological stations in Romania (Bucharest, Iasi, Cluj-Napoca and Constanta) and four stations in Ukraine (Lviv, Ivano-Frankivsk, Uzhgorod and Chernivtsi) using daily 2-m temperature observational data for period 1961-2010. The shifts were determined based on annual courses of multi-year daily mean temperature for standard WMO (1961-1990) and modern (1981-2010) climatic periods. Two types of data were used: in situ measurements and E-OBS gridded dataset. The most significant changes in duration were found for the following seasons: duration of warm season (t > 0°C) increased by 15 days in Constanta, duration of frost-resistant vegetation season (t > 5°C) decreased by 6 days in Bucharest, and duration of active vegetation season (T>10°C) decreased by 5 days in Chernivtsi. The mean absolute error between E-OBS dataset and measurements equal 2 days for Romanian stations and 1.4 days for Ukrainian stations for all seasons have been found