Statistical evaluation of temporal changes in annual precipitation in the plain territory of Ukraine
Authors:   State Emergency Service of Ukraine National Academy of Ukraine, Ukrainian hydrometeorological institute, Kyiv, Ukraine, Palamarchuk Liudmyla V. , Shedemenko Iryna P. ,   Institute for Safety Problems of Nuclear Power Plants National Academy of Sciences of Ukraine, Kyiv, Ukraine
Published: June 2021

The field of precipitation of the plain territory of Ukraine is investigated according to the data of evenly spaced 18 weather stations. The annual precipitation is analyzed for periods of different duration (from the beginning of observations at the station until 2015) and for the period 1961-2015. The main statistical characteristics are calculated, the patterns of their changes in the study area are shown. Gradient of decrease in multi-year annual precipitation for 1961-2015 (650 to 400 mm) directed from the northwest to the south and southeast of the country. The value of positive skewness and kurtosis, the coefficient of variation (0.16-0.26), on the contrary, increases in this direction. The standard deviation (91-137 mm) is maximum in the southwest and in the center of the plain part of Ukraine. It was determined that the distribution of annual precipitation can be considered normal, mainly with positive skewness and kurtosis. Multi-year fluctuations in annual precipitation are approximated by linear trend equations and a polynomial of the 6th degree. Regions with a negative and positive linear trend of annual precipitation in 1961-2015 were identified. A downward trend in precipitation was noted at stations located in a “strip” from the southwest (Chernivtsi) to the northeast (Sumy) through the center of Ukraine. In the south-west of this region (Vinnytsia), the decrease in precipitation is the greatest: the negative linear trend is statistically significant, the slope of the trend is -2.35, the coefficient of determination is 0.14; mean annual precipitation for 1991-2015 compared to 1961-1990 less by 10.5%, 53.4 mm. In the rest of the plain territory of the country, there was a tendency towards an increase in precipitation, but the positive trend for all stations is statistically insignificant. The absence of statistically significant linear trends (except for Vinnytsia) can be explained by the relative stability of the multi-year precipitation regime during this period. The use of a more complex approximation and a long time series of observations increased the trend approximation confidence, but the influence of these factors is not unambiguous for all weather stations. On the graphs of polynomial trends, the cycle manifestation in the time series of annual precipitation depends on the length of the observation series and decreases from west to east of Ukraine. The duration of the cycles is 25-30 and 35-40 years when determined according to the data of 1961-2015, and from 70 to 90 and 120 years according to the series of observations more than 100 years. In 2016-2025, as shown by estimates by the equations of polynomials of the 6th degree, a decrease in annual precipitation will prevail on the plain territory of Ukraine compared to 1961-2015. The largest decrease (by 10-13%) is likely in the central regions (Poltava, Dnipro). an increase (by 5%) - in the southwest (Vinnitsa, Chernivtsi).