An analysis of daily ice coverage changes for the Yenisei River from 2002 to 2021

Since the beginning of the 20th century, the surface air temperature in the Arctic has increased more than three times faster than the global average. River ice is an important component of the terrestrial cryosphere, which is very sensitive to air temperature. The Yenisei River originates from the Sayan Mountains in Mongolia and is the largest watersheds drained by Arctic Ocean, which covers latitudes from 46°N to 73°N. The changes of river ice for Yenisei River provides reflect the response of great rivers in the high latitudes of the Northern Hemisphere to climate change. In this study, the daily river ice coverage in the Yenisei River was firstly estimated with a grid of resolution at , derived from the Moderated Resolution Imaging Spectroradiometer (MODIS) daily observations for the period 2002-2021. The classical Normalized-Difference Snow Index (NDSI) algorithm was employed to extract the ice cover; a cloud removal and filtering method were used to reduce errors caused by cloud contamination and the polar night influence. The validation with dependence to the Landsat data showed that an overall accuracy was achieved by 86%. By applying the Theil–Sen nonparametric statistical slope method and the Mann–Kendall test to the results, it was found that the river ice coverage shows a decreasing trend. Over the past 20-year period, 82.8% of the Yenisei River Basin experienced a decreasing ice coverage, of which 21.9% is significant at the 0.05 level of significance. A correlation analysis indicated that the winter river ice coverage is driven by the mean winter air temperature () and that the ice coverage shows a strong latitude dependence (). River ice coverage is highly sensitive to the air temperature in the south part of the Yenisei basin, where the latitudes are low and the altitudes are high. It was also found that, during the winter, the accumulated negative temperature correlates with river ice coverage similarly with the average temperature (). In Lake Baikal, the largest freshwater lake in the Yenisei basin, apart from air temperature the distribution characteristics of ice coverage was most probably affected by heat inflows from streams, dynamics and water depth.