Analysis of Homogeneity and Stationarity of Freeze-Up Observation Series in the Prypiat River Basin within Ukraine

Abstract

Summary The investigation of the formation conditions, tendencies of freeze-up on the rivers is of very practical importance, because it has an impact on hydropower, shipping, fisheries, etc. Such studies are relevant for the Prypiat River basin (within Ukraine), because the last investigation of freeze-up was carried out more than 10 years ago. In this paper results of the complex analysis of freeze-up observation series tendencies investigations based on using the statistical and graphical methods in the Prypiat River basin are represented. So, for the research the Mann-Kendall non-parametric statistical test, mass curve, residual mass curve and combined graphs. Such an approach allows us to obtain more reliable results of research. In the Prypiat River basin the freeze-up observation series of 29 gauges were used with the period of records from the beginning of the observations to 2020 inclusive. In the Prypiat River basin the majority freeze-up observation series are quasi-homogeneous and quasi-stationary, as it has only an increase and a decrease phases of long-term cyclical fluctuations, which are also unfinished. Since the 90th years of the past century the appearance of the freeze-up occurs at later dates, the break-up of freeze-up occurs at earlier dates which causes shortening of its duration.