ИСТИНА

Heat and cold waves are significant and dangerous climate anomalies. Hence, assessing changes in heat and cold waves is crucial both for Russia and the world. Worldwide research shows that climate extremes are becoming stronger nowadays and this implies a growth of frequency of heat and cold waves. Defining a criteria of extreme events depends on the choice of thresholds. In this paper we consider the thresholds for determining the heat wave as the value of 95th percentile of maximum temperature distribution, and the cold wave as the value of 5th percentile of minimum temperature distribution. Changes in the number, intensity and duration of heat and cold waves in Russia for various periods from 1951 to 2010 were evaluated according to this rule. The purpose of work is to estimate changes in the number, duration and intensity of heat and cold waves in Russia as factors of the natural discomfort. Heat waves were classified by the level of discomfort. Analysis of the results shows an increase in the number of days with abnormally high temperatures, since the 1990s of the XX century. The most significant increase is seen in the European part of Russia and the Far East. Heat load growth was detected up to absolutely and extremely adverse values during the period of contemporary climate warming. It was mainly caused by the increase in the number of days with high temperatures. These changes are particularly evident for regions in the northeastern part of Russia and the European Territory. A decrease in cold waves as well as a growth of minimal temperatures was observed in winter in much of Russia since lately 1990s. However, these tendencies are weakening in the beginning of the XXI century: a significant area in Southern Siberia is seen where cold waves are becoming stronger and minimal temperatures are decreasing. Researches were supported by Russian Science Foundation (RSF) grant № 16-17-10236.