Runoff fluctuations in the Selenga River Basin

The Selenga River has historically provided 50% of the total freshwater water input to the Lake Baikal, transporting substances and pollutants that can considerably impact the unique lake ecosystem. In the context of on-going regional to global change, we here aim at identifying and understanding mechanisms behind spatial and temporal variability and trends in the flow of the Selenga River and its tributaries, based on hydrological and meteorological station data (since the 1930s), remote sensing, and statistical analyses. Results show that the flow of the Selenga River exhibits cycles with phases of high flows lasting 12 to 17 years and phases of low flows that historically lasted for about 7 years. However, despite an asynchronous behavior between right-bank tributaries and left-bank tributaries, the flow of the Selenga River near its delta at Lake Baikal has now been low (30% below the 1934–1975 average) for as long as 20 years, due to reduced input from precipitation, particularly during the summer season. Observed decreases in annual maximum hourly flows and decreases in annual minimum 30-day flows are consistent with increasing activation of the groundwater system due to thawing permafrost, and higher winter temperatures that support increased winter flows by preventing rivers to freeze from top to bottom. These recent and relatively large changes have implications for regional water planning and management, including the planned large-scale hydropower expansion in the upper part of the Selenga River Basin.