Probabilistic characteristics of the freeze-up duration on the rivers of the Prypiat basin within Ukraine

Abstract

The freeze-up those forms on rivers in the autumn-winter period significantly impacts on the hydrological, hydrochemical, biological processes of rivers, as well as the work of hydropower, shipping, fisheries, etc. In modern conditions, the formation, duration, and break-up of freeze-up on rivers occurs under the influence of natural, anthropogenic factors and climatic changes. Therefore, the research of modern trends of the freeze-up duration on the river and the determination of its calculation characteristics is an urgent task. Traditionally, the multi-annual mean, minimum and maximum values of the freeze-up duration on rivers are determined. Such indicators are important, but they still provide a rather limited knowledge about the freeze-up over a period of time. Expand knowledge about the variability, magnitudes, duration, dates of appearance freeze-up and break-up can by determining its probabilistic characteristics, but such research have not been carried out for the rivers of Ukraine, including for the rivers of the Prypiat basin. The objective of this paper is to determine the probabilistic characteristics of the freeze-up duration of the rivers of the Prypiat basin within Ukraine, as well as the analysis of the obtained results. The data of 29 water gauges were used for the period from the beginning of observations to 2020, inclusive. As statistical parameters of the analytical distribution of the freeze-up duration, the multi-annual mean value, the coefficient of variation and the coefficient of asymmetry were used. The Pearson distribution of type III was used to created analytical curves of the freeze-up duration, and the Weibull formula was used for the empirical distribution of the freeze-up duration. In this paper, the probabilistic characteristics and statistical parameters of the freeze-up duration on the rivers of the Prypiat basin within Ukraine are determined. The probability distribution of Pearson type III quite satisfactorily describes the empirical points of the freeze-up duration on the rivers of the Prypiat basin within Ukraine. The vast majority of the analytical curves of the distribution of the freeze-up duration have a negative asymmetry. Only 8 the analytical curves have a positive asymmetry. In the Prypiat Basin within Ukraine the multi-annual mean of the freeze-up duration is 69 days and ranges from 26 to 95 days. The values of the asymmetry coefficients are small and vary from 0.01 to 1.02 for positive values and from -0.03 to -0.60 for negative values. The coefficients of variation change within small limits from 0.34 to 0.79. Probabilistic characteristics can use for the design and operation of any hydrotechnical structures, as well as the work of economic sectors that are related to the use the rivers. In addition, the research results can be used for further research, namely any search for prognostic dependencies, generalizations, zoning, etc.