Trends and fluctuations of river ice regimes in the Prypiat Basin, within Ukraine

Information about the formation, destruction, and duration of river ice regimes is especially important for hydropower, shipping, fisheries, etc. Research into modern trends in river ice regimes and their spatial and temporal fluctuations is essential, especially in a changing climate. This study examines the trends and fluctuations of air temperature and ice regimes based on series of observations in the Prypiat River basin within Ukraine. Air temperature data from 17 meteorological stations and ice data from 29 water gauges were analyzed. A complex analytical approach involving statistical and graphical methods was employed. The Mann-Kendall statistical test, mass curve, residual mass curve, and combined graphs were used in the study. In the Prypiat River basin within Ukraine, observations of mean monthly air temperature, ice occurrence, freeze-up, and their duration are homogeneous (quasi-homogeneous) and stationary (quasi-stationary). The quasi-homogeneous and quasi-stationary characteristics are explained by the presence in the observation series of only increasing and decreasing phases of long-term cyclical fluctuations, which are incomplete. The trends of air temperature and ice regime correspond strongly, indicating the defining role of air temperature in the formation of ice occurrence and freeze-up. Since the end of the 1990s, the warming phase of air temperature in the autumn-winter period determines the appearance of ice and freeze-up later in the year. In March, the warming trend in air temperature, which began after 1988, determines the freeze-up, break-up, and disappearance of ice earlier in the year. Thus, the duration of ice and freeze-up on the rivers has decreased.