The intra-annual streamflow distribution of Ukrainian rivers in different phases of long-term cyclical fluctuations

Abstract

In this article, the analysis of homogeneity and stationarity of the mean monthly discharges of the rivers of Ukraine was carried out by means of hydro-genetic methods with the use of observation series on 305 water gauging stations from the very beginning of the observation till 2010 inclusive. An integral curve was used for the estimates of homogeneity of the observation series. Difference-integral curves were used for estimation of stationarity of the observation series and for the study of their long-term cyclical fluctuations. It turned out that most series of the mean monthly discharges were homogeneous. The observation series that have a full cycle of long-term cyclical fluctuations (dry and wet phases) are stationary, whereas other observation series are quasi-stationary. The intra-annual streamflow redistribution occurs depending on dry and wet phases of long-term cyclical fluctuations. It is shown that the terms, the duration of periods and seasons of intra-annual streamflow distribution should define cyclical fluctuations because the mean monthly discharges change in dry and wet phases. Therefore, it is necessary to carry out development of the schemes of the components of intra-annual streamflow distribution for the rivers of Ukraine because such schemes were defined on the short observation series in 50–80s of the 20th century without considering a long-term cyclical fluctuation streamflow.