Flood Hazard Within the Basins of the Left Tributaries of the Angara

Abstract

In June and July 2019, on the left tributaries of the Angara river there occurred catastrophic rainfall floods inflicting enormous damage and human victims. The greatest damage was experienced by the city of Tulun on the Iya river. A comprehensive characteristic is given to the 2019 floods in comparison with similar events of the historical past and from the period of instrumental observations. An analysis is made of the characteristics of the flood hazard at gauging stations: their frequency and impact. The homogeneity of the series of the peak flood runoff is estimated against the background of climate change. The objects for study were the basins of the left tributaries of Angara river: the Irkut, Kitoi, Belaya, Oka, Uda and Biryusa, with a more detailed characteristic for the Iya river basin. The floods of 2019 were formed by extreme precipitation on the previously moistened surface of the catchments. In 2019, an exceptional hydrological situation developed in terms of both flood hazard characteristics and the devastating consequences for the city of Tulun. Nevertheless, catastrophic floods of a similar magnitude also reoccurred in the historical past and during the period of instrumental observations. The situation with two extreme floods during the summer season is also not unique. The event under study cannot yet be associated with climate change. Changes in the peak rainfall runoff series are mostly insignificant, even when the approximate runoff maxima of 2019 are taken into account. The decreased flood frequency over a later period may be associated with a low-water period that ended in 2019. Therefore, similar events can be expected to recur on the rivers of Irkutsk oblast, both within the Angara basin and within the Lena and South Baikal basins.