Long-term Variations of the Thermal Regime of Lake Bol’shoe Miassovo (South Urals) as a Result of the Climate Warming

A. G. Rogozin and S. V. Gavrilkina

Analyzed is the cycle of ice cover lifetime for a typical lake in the South Urals corresponding to the 11-year cycle of solar activity. It is revealed that the amplitude of oscillations of the ice cover life- time gradually decreases as the contribution of the cyclic component lowers and the impact of the irregular component increases. The linear trend demonstrates it gradual decrease with the rate of about 0.3 day/year. Observed is the long-term trend of the considerable lag of the beginning of freezing-over (by 0.3 day/year). The maximum annual temperature of the bottom water layer increased by 2.9°C from 1986 to 2011 with the rate of about 0.1°C/year. It varies cyclically (the period is 5 years) and feebly depends on the cycle of ice cover lifetime. The obtained data not only indicate the primary role of natural reasons in the observed water temperature rise in the reservoirs but also enable the conclusion on the increase in the anthropogenic contribution to the climate warming.