Features of seasonal runoff from waterlogged catchments of the Ob-Irtysh interfluve in terms of regional climate change

Here are shown the results of search of climate changes in the river flow from wetland catchments which are located on the ridges of the Great Vasyugan Mire in its northern and north-eastern parts, as well as within the southern taiga of the Irtysh area. It is located within the administrative boundaries of Tomsk and northern part of Novosibirsk Oblasts. It is known that climate changes are manifested primarily in the seasonal runoff. In this regard, the work consists of two parts. The first is devoted to the theoretical problem of the accuracy in determination of the volume of the seasonal runoff. It is solved by means of a comparative analysis of the flow calculated from the position of the calendar and genetic approaches of identification of the boundaries of the seasons and involves obtaining an answer to the question of to what extent the establishment of unified calendar dates of the onset of hydrological seasons distorts the true trends in the seasonal runoff in a changing climate. Basing on the extensive material of analysis, significant differences in the length of seasons and in volumes of seasonal runoff were observed. For the territory the greatest discrepancy is characteristic for floods which, in average for the period of time, is 19 - 39 days shorter than the one determined according to the calendar method. The winter low water period, on the contrary, is 13 - 25 days longer; the summer-autumn low water period may be either shorter (6 days) or longer (26 days). In percentage, the difference in calculating of the winter low water in the annual is on average within 0.6 -7.0 %, spring flood 1.2 - 11.5 % and summer-autumn low water period 0.1 - 9.8 %. However, for some years the discrepancy between methods for the spring flood can reach 45 %. The discrepancy between methods is stronger in low water years. It is justified that the approach of the calendar when defining the season boundaries underestimates the volume of winter low water and overstates the amount of floods. Thus, the correct solution of tasks of a scientific nature, especially those associated with the analysis of the tendencies and the forecast, is possible only when a genetic approach is used for determining the timing of seasons. The second part is devoted to the analysis of the spatial-temporal distribution and dynamics of the seasonal flow which are calculated from the positions of the genetic approach to the area during the recent decades. Here are demonstrated the quantitative characteristics of the modules of the seasonal runoff and the results of athe nalysis of their trends over the study period (1985-2009). In general, the territory is characterized by the presence of divergent trends of changes in the seasonal runoff, including statistically significant ones. In the winter low water period, rivers with an increasing runoff dominate. A characteristic feature for the runoff of the south taiga of the Irtysh area is marked. It is a simultaneous increase of the flow in all seasons and during the year in general in the majority of locations.

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