RELATION OF EXTREMES OF MINIMUM WINTER RIVER FLOW WITH TEMPERATURE AND ICE FACTORS

Abstract

Studies performed in different river basins in the North-West of Russia have shown that a combination of temperature and ice conditions plays a significant role in changing the winter water content of rivers. Air temperature and ice thickness are integral indicators of changes in thermal conditions in the river basin and in the river, regulating through cryogenic processes the supply of groundwater and its discharge into rivers in winter. Therefore, the main predictors used in the work are air temperature, ice thickness, and winter river flow. To obtain quantitative estimates, a comparative analysis of changes in river flow by the end of winter under different temperature and ice conditions was performed. The series of winter runoff of rivers in the basins of the Lovat, Syas, Northern Dvina and Onega rivers with the total period of observations of the runoff and the thickness of the river ice are analyzed –1955-2016 years, temperature – 1936-2016 years. Based on the analysis of a series of observations of river flow, ice thickness, and air temperature lasting more than 50 years, it is concluded that the lowest values of the minimum winter flow of rivers were observed in cold winters, and the highest values were observed in milder winter seasons. With comparable pre-winter water content of rivers in a series of mild non-thawing winters, river flow in the studied basins decreased less intensively and the minimum winter flow was higher on average by 10-20%, and in some cases more.