Air temperature as a basis for long-term forecasting of break-up ice at the Dnipro cascade reservoirs

Abstract

The ice regime on water bodies depends on large-scale atmospheric processes that develop over large areas and over a long period of time. The basis of long-term forecasts of the ice regime on water bodies are assumptions about the uniformity of atmospheric processes during the synoptic season and the regularity of their trends from season to season. The most widespread approach to long-term forecasting is based on finding relationships between the quantitative indicators of atmospheric circulation over the forecasting object or over separate adjacent (large in the area) synoptic areas or zones and the terms (dates) of ice phenomena appearance (more often their deviation from the norm). Long-term forecasting of ice regime of the Dnipro Cascade reservoirs is very important, first, for the operation of hydroelectric power stations. In addition, such forecasts also ensure the work of other sectors of the economy, namely shipping, fisheries, utilities, etc. Forecasting the terms of break-up ice at the reservoirs is necessary to determine the terms, depth of spring triggering of the reservoirs, and safe transit regime of spring ice run through the Dnipro Cascade. At the same time, there are no methods of the long-term forecasting of break-up ice terms at the Dnipro Cascade reservoirs. Note that the break-up ice at the rivers of Ukraine is largely determined by the air temperature in February (Huseva A.A., 1947). Therefore, the main objective of this research is the determine of the relationship between the mean air temperature for the first decade of February and the break-up ice dates at the Dnipro Cascade reservoirs, as well as to using possibilities assessment of obtained results for the long-term forecasting. The research the used the break-up ice dates at 38 water gauges which are located at the banks of 6 reservoirs of the Dnipro Cascade, as well as the mean air temperature for the first decade of February. This information was obtained from published reference materials prepared by the Central Geophysical Observatory named after Borys Sreznevsky (Kyiv). The research period at each water gauge was taken depending on the water filling year of each reservoir and to 2020, inclusive. Response evaluation of freeze-up at the Dnipro Cascade reservoirs to changes in the air temperature of February were determined by the calculated correlation coefficients between the break-up ice dates and the mean air temperature for the first decade of February. The analysis of observation series for the break-up ice dates at the Dnipro Cascade reservoirs showed that the data of 3 water gauges, namely the Kaniv reservoir - Vyshhorod town, Kamianske reservoir - Svitlovodsk town and Dnipro reservoir - Kamianske town have a significant anthropogenic influence. So, the information about these water gauges was excluded from further research. The break-up ice dates at the reservoirs are characterized by considerable variability. Correlations between the break-up ice dates and mean air temperature for the first decade of February are classified as the medium relationships. As a result, the forecasting dependencies have the rather low quality criteria. Hence, to obtain more acceptable results is necessary to expand the search other predictors of atmospheric processes both in space and time.