ASSESSMENT OF THE MODERN CLIMATE CHANGE IMPACT ON THE ICE REGIME CHARACTERISTICS ON THE RIVERS IN THE NORTHERN DVINA BASIN

The main danger on the rivers of the Northwestern Federal District, in which the Northern Dvina Riverbasin is located, is posed by powerful ice jams, the highest levels of which are also the maximum annual levels. Longterm series of characteristics of the ice regime on the rivers of the Northern Dvina basin – the dates of the beginning andend of the freeze-up period, its duration, maximum ice thickness, the highest water levels at the beginning of ice formationand during the period of ice drift – are approximated by models of a non-stationary mean in order to identify the impactof modern climate change. In the course of the study was developed a methodology for evaluating the effectiveness andstability of the parameters of non-stationary mean models. It has been found that over the observation period the freezeup duration decreased by 17 days on average, the date of the beginning of the freeze-up period started to be observed 12days later, and the date of its end – 5 days earlier. The maximum ice thickness on the rivers decreased by 9 cm, themaximum levels of ice drift decreased by 71 cm on average, while the levels of the beginning of ice formation practicallyhave not changed. The sums of negative temperatures in the winter period, as the main factor determining the maximumthickness of ice and the duration of the freeze-up, decreased at meteorological stations in the Northern Dvina River basinby an average of 320 °C, or by 21%. In the southwest of the territory, this decrease occurred back in the late 1980s dueto the strengthening of the winter NAO index, and in the rest of the territory – in the early 21st century due to the beginningof the warming in the Arctic. The changes exceed the natural variability in several points.The impact of climate change on the characteristics of ice phenomena occurs with a delay and possible distortiondue to the inertia of cryospheric processes. This delay period depends on the local characteristics of the observationsection and the section along the river bed. Therefore, the years when these changes will affect the ice regime characteristics at different observation points may differ.