Water regime of lake Baikal under conditions of climate change and anthropogenic influence

Based on water level data, we have studied some specifics of the water regime in Lake Baikal associated with the warming climate, which has intensified since the early 1970s. We have also addressed the overregulation of the lake after the construction of the Irkutsk Hydroelectric Power Station (IHPS). We have estimated the influence of climate on the water regime of the lake through observing the change in the surface water inflow from the watershed basin and the characteristics of runoff from the three largest Baikal rivers: the Selenga, the Upper Angara and the Barguzin. A decrease in the runoff of these rivers during the intensification of warming reduced the surface water inflow into the lake, causing a decrease in level between 1976-1981 and 2014-2017. Notably, the spring flood on the rivers during climate warming becomes shorter and is characterized by a decrease in the maximum water discharges, contributing to the slowdown of the filling of Lake Baikal during spring and summer. Contrastingly, in the winter, river runoff and the lake inflow increase with the rise in air temperature. However, this increase depends on the runoff of rivers during the previous summer and autumn. This runoff determines the formation of groundwater reserves that serve as the main source of riverine water in the winter. We have suggested the possible decrease in runoff during the years of the air temperature rise due to an increase in evaporation. Warming also contributes to the increase in evaporation from the watershed of Lake Baikal, as well as the rate of decline in its water level, which reaches 10-15 cm per month in November and December. The backwater from the dam of the IHPS has been observed in Baikal since the autumn of 1958; it has caused an increase in the lake level by an average of 0.79 m. Within the year, there was an alignment of outflow from the lake through the Angara River, and in periods with low water level, it was kept at a minimum value of 1300 m(3)/s for a long lime in order to maintain the Baikal water level. Using indirect data, we have investigated the fluctuations in water level of Lake Baikal between 1729 and 2017, which indicates its potential increase at a rate of 1 cm per 10 years. The changes in the Baikal water regime determine the restructuring of various processes inside the water body and are important for the ecosystem of the lake.