– The classic annual streamflow pattern is the following: full water in May and June, followed by the summer low-water period; then come the fall freshets caused by heavy rainfall; and finally, the winter low-water period, when the ground freezes, the river is covered in ice, and water levels drop. But the climate is changing, and precipitation in the past decade’s winters has increasingly been in mixed form or even rain. This leads to winter freshets and rising river levels, as rivers fail to freeze over, – said Aleksey Tolstikov, Head of the Hydrology and Geography Laboratory at the Northern Water Problems Institute (NWPI KarRC RAS).
The fall and winter high-water periods now often exceed the water volume of the spring full-water period due to their duration. The average start date of cold-season freshets on rivers of the Baltic Sea basin (the Shuya, Suna, Vidlitsa, Olonka, Vodla, etc.) is September 29, and the end date is February 1. The corresponding dates for rivers of the White Sea drainage basin (the Chirka-Kem, Vyg, Kuzema, Ukhta, etc.) are September 17 and January 29. Sometimes, a high-water phase started in January and persisted until the onset of the spring flood. So, a redistribution of the river runoff is happening throughout Karelia, with peaks and lows occurring almost simultaneously across all watercourses. There are also reports of similar phenomena occurring in other northern regions. Scientists attribute these changes specifically to the influence of global climate processes.
The results of the study were published in the scientific journal Transactions of the Karelian Research Centre RAS (Limnology and Oceanology Series).
Aleksey Tolstikov, Head of Hydrology and Geography Laboratory, Northern Water Problems Institute KarRC RAS
– The conclusions are based on a multidecadal data series. Surely, every year is different: the weather now is frosty and the rivers are ice-covered. There are years with low and with high water volumes in rivers: last year, e.g., the water content was low. Yet, we took a period permitting a representative analysis and find that the trend is steady, despite the occurrence of low-water years, – commented Aleksey Tolstikov.
The natural processes can affect humans. E.g., a partially frozen river can get ice jammed and heavy rainfall would cause a local water level rise and overflowing. The situation with unsteady freeze-up is critical for ice crossings, which are of high relevance for some regions, such as the Arkhangelsk Region. High humidity in winter can affect metal structures.
– Research carried out at our institute proves that the climate change has been altering the structure of lake ice, making it brittle. The warming and flooding processes also influence its properties: if the water level in a reservoir or a stream rises sharply, water seeps up through cracks in ice and impregnates the snow. The ice cover loses strength, – noted Aleksey Tolstikov.
Considering the changes, it’s crucial that people mind the ice safety rules and follow the guidelines of the Karelian Emergency Authorities when planning their wintertime outdoor activities.