Floods in Siberian river basins

In the article the causes of floods in the basins of three major rivers - the Ob (with the tributary Irtish), the Yenisei (with the tributary Angara) and the Lena are given. The floods can be territorial which covere up to 50-60% of the total area or the floods can be local which are formed on separate reaches of rivers or in limited areas of the region. According to the frequency of maximum water level the following subdivisions are made to distinguish the characteristics of floods: extreme flooding - with a frequency to 1%; severe flooding - with a frequency from 1% to 10%; heavy flooding - with a frequency from 10 to 25%. The examples of territorial and local flooding, the spatial and temporal variation of floods, ambiguity of cause-effect connections and laws governing the formations of maximum runoff, and experience of the operational forecasting of floods in West and Middle Siberia are presented in this paper.