Analysis of the dynamics of time characteristics of the seasons of the year in the sub-boreal forest (sub-taiga) of the West Siberian plain in the period from 1936 to 2015

Climate change is one of the main today'schallenges. Over the past 130 years the world's temperature has increased approximately by 0,85°C. Sub-boreal forest (sub-taiga) is a natural zone located on the transition from the Southern taiga to broad-leaved forests in Europe and the Far East or to the forest-steppe in Siberia. In physiographic terms the West Siberian sub-boreal forest (sub-taiga) is the southernmost latitude climatebelt in the subzone of the Southern taiga of the West Siberian plain. The climate belt includes mixed light coniferous, parvifoliate, and grass layer's forests locatedbetween 54 and 56° N (Fig. 1). Т1ю choice of the study area is explained by the fact that the biodiversity of the sub-boreal forest (sub-taiga) ecosystems is the highest among the ecosystems of Western Siberia. At the same time the sub-boreal forest (sub-taiga) of the West Siberian Plain is the most developed zone of the region, experiencing and being sensitive to diverse external factors, including climatic ones. In economic and geographic terms sub-boreal forest (sub-taiga) of Western Siberia is occupied by part of the Tomsk and Tyumen regions, which are investment-attractive subjects of Russia. In this regard, in order to develop a strategy for social and economic development of the territories and to substantiate the material and financial costs of enterprises, climate monitoring including studies of the temporal characteristics of the climatic seasons of the year at the regional level is needed. This article examines changes in temporal characteristics (start dates, end, duration)of seasons in the period from 1936 to 2015, in-sub-boreal forest(sub-taiga) of the West Siberian plain, derived from the schedule of average years of average daily air temperature. The foundation of our research was comprehensive genetic method of climate study of N.N.Galakhov and N.V. Rutkovskaya. For the entire study period (from 1936 to 2015), a positive tendency of the air temperature change in sub-boreal forest (sub-taiga) with almost synchronous coefficient of the linear trend: +0.25°C / 10 years in Tyumen and +0.26°C / 10 years in Tomsk is observed (Fig. 2). On the basis of the obtained daily average air temperatures from 1936 to 2015, we have found the average long-term boundaries of the seasons and their duration for the three above periods (Table). The analysis shows that in the sub-boreal forest (sub-taiga) of the southeast of the West Siberian Plain the climate warming has been observed since the 1970s. Spatio-temporal trends in the dynamics of the dates of the beginning and the end of the seasons of the year in sub-boreal forest(sub-taiga) were revealed: 1) there is a shift in time characteristics from the first period to two subsequent ones: the dates of the beginning of the spring and summer seasons shifted back and start earlier, the dates of the beginning of the autumn and winter seasons - later, and the dates of the end of the winter and spring seasons - earlier; 2) the duration of the seasons of the year changes as well as the ratio between them in the annual cycle; 3) domination of different seasons of the year is revealed: in Tyumen - of summer, in Tomsk - of winter; 4) sharper changes in temporal characteristics in the western part of the sub-boreal forest (sub-taiga) of Western Siberia; 5) recorded a difference in the duration of the main seasons - more than two weeks, and winter - more than a month. Analysis of the dynamics of natural seasonal rhythms' temporary changes makes it possible to estimate the changing conditions of landscape functioning and to examine the directions for their further development and organization of human economic activity.

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