Modern Changes in the Thermal Regime of Mountain Rivers in the Permafrost Zone (A Case Study for the Upper Kolyma)

M. V. Ushakov and N. V. Ukhov

The changes in the thermal regime of the Upper Kolyma rivers in the permafrost zone in 1981–2010 are discussed. Over the recent three decades the normals of the dates of the springtime 0.2C water temperature crossing have shifted by 3–13 days earlier due to the climate warming. Average long-term water temperatures in the first half of summer increased by 1.4–1.6C. In autumn, the 0.2C crossing occurs on average by 9 days later. This agrees with an increase in air temperature normals. However, in the second half of the warm period, annual mean water temperatures dropped by 0.7–1.5C. Such abnormal response to climate change is caused by the involvement of an additional volume of chilled water to the river flow due to the thawing of permafrost and the expansion of taliks in August and September.