Trends in Russian Arctic river-ice formation and breakup, 1917 to 1994

Long-term time series of river-ice observations for nine large rivers in Arctic and subarctic Russia are analyzed using the Mann-Kendall test for monotonic trend. Of eight data categories analyzed for each river, the timing of melt onset displays the highest incidence of change, with statistically significant negative (earlier) shifts of approximately to 3 weeks found for the Pechora, Ob, Olenek, Indigirka, and Kolyma rivers. However, corresponding shifts in associated ice-breakup phenomena are not found, suggesting an increase in spring melt period and a transition to more thermally driven ice-breakup events. An observed general pattern of decreased ice cover in the 1950s, increased ice cover in the 1980s, and subsequent decrease during the 1990s is generally consistent with other studies of Siberian temperature trends. However, both interannual and regional variability is found. Earlier occurrence of autumn freezing is found for the Onega, Varzuga, Mezen, and Yenisei rivers, leading to an increase in the duration of winter ice cover for all but the Mezen. An opposite trend is found for the Indigirka and Kolyma rivers of far eastern Siberia. This regional contrast is attributed to North Atlantic modulation of western rivers.