ЙМОВІРНІСНІ ХАРАКТЕРИСТИКИ І СТАТИСТИЧНІ ПАРАМЕТРИ СТРОКІВ НАСТАННЯ ОСНОВНИХ ФАЗ ЛЬОДОВОГО РЕЖИМУ РІЧОК БАСЕЙНУ ПРИП’ЯТІ У МЕЖАХ УКРАЇНИ

Abstract

Probabilistic characteristics of the water body ice regimes significantly expands knowledge about their variability, magnitudes and appearance timing of main phases. Such knowledge is important for the design and operation of hydraulic structures. Along with this, the probabilistic characteristics of the river ice regimes of Ukraine were calculated in the 70s of the 20th century, including for some rivers of the Pripyat basin. Therefore, the main objective of this research is to determine the probabilistic characteristics and statistical parameters of the appearance dates of main phases of river ice regimes, namely appearance date of ice, date of freeze-up, break-up date (i.e., melt onset), date of ice disappearance in the Prypiat River basin within Ukraine, as well as the analysis of the obtained results. The research was carried out based on the data of 29 water gauges for the period from the beginning of observations to 2020. Such indicators as the multi-annual mean, standard deviation and asymmetry coefficient were used as statistical parameters. The analytical distribution of the appearance dates of main phases of river ice regimes is determined by the Pearson curve of type III, and empirical distribution is determined by the Weibull formula. Statistical series of the appearance dates of main phases of river ice regimes were arranged from early to late dates, namely low probability values were assigned to early dates, and large probability values were assigned to later dates. Pearson probability distribution of type III quite successfully describes the empirical points of main phases of river ice regimes of the Pripyat basin within of Ukraine. Analytical distribution curves have a slight negative asymmetry for the dates of the ice appearance and freeze-up, and a positive asymmetry for the dates of the break-up and ice disappearance. The variability of standard deviation and multi-annual mean of the appearance dates of main phases of river ice regimes is within ±7.5-10 days and 3-4 weeks, respectively. In general, the appearance dates of main phases of river ice regimes, as well as their statistical parameters and probabilistic characteristics have close values that are subject to geographic zoning. The analysis of changes over time in probabilistic characteristics and statistical parameters of the dates of ice appearance and freeze-up showed that the greatest changes have by probabilities that are not repeated often, and the smallest – by multi-annual mean and asymmetry coefficients.