Long-term forecasting of appearance dates of ice phenomena and freeze-up at the Dnipro Cascade reservoirs by teleconnection indicators

Long-term forecasting of the ice regime of water bodies is a difficult task and is still unresolved in the part of improving the accuracy of forecasts. The objective of this paper is the development of the long-term forecasting methods of appearance dates of ice phenomena and freeze-up at the Dnipro Cascade reservoirs by teleconnection indicators. The research was carried out based on the observation data of 38 water gauges, which are located on 6 reservoirs of the Dnipro Cascade. The appearance dates of ice phenomena and freeze-up for the period from the observation beginning at each water gauges to 2020, inclusive, were used. In addition, in the research were also used the information about the teleconnection indicators, namely 34 atmospheric indices, sea surface temperature indices, teleconnection indices and patterns, that are determined by the National Weather Service (NWS) of the National Oceanic and Atmospheric Administration of United States of America (NOAA USA). The long-term forecasting methods of the appearance dates of ice phenomena and freeze-up at the Dnipro Cascade reservoirs were developed by searching for the best correlation or regression relationship between dates and teleconnection indicators. The probabilities of acceptable error of the developed methods are in the range of 61–72%, which corresponds to the category of "satisfactory" assessment of the method quality. It makes it possible to recommend them for use in operational forecasting.