Modern Climate Changes in the Selenga Mid-mountain Region and their Reflection in Rivers Runnow and Tree Ring Chronologies

Based on data from 7 meteorological stations, the main parameters (surface air temperature, precipitation, aridity and humidification indices) characterizing climate trends for 1950–2021 were considered on the territory of the Selenga midlands (The Republic of Buryatia), and their influence on river flow and radial growth of Scots pine. A significant increase in surface air temperature is shown, occurring with a high degree of consistency at different weather stations. The average value of the linear trend for the territory for the general period was 2.1°C. The most intense increase in temperature and increase in the frequency of above-zero anomalies has been observed in the last 11 years (2011–2021). In the precipitation regime during the study period, two complete moistening cycles were identified (1961–1981 and 1982–2018) lasting 21 and 37 years. Currently, there is a humid phase, which began in 2019. An increase in temperature leads to increased aridity of the region, which is especially noticeable during the arid phases. The cyclicity characteristic of the precipitation regime is also manifested in long-term changes in river flow. The river’s water flows are most dependent on precipitation. Selenga. However, the synchronicity of their changes is not observed throughout the entire time series. In the precipitation regime, the phase of reduced moisture at the beginning of the 21st century is not as clearly expressed as in the runoff regime. The same differences were revealed in the flow regime of different rivers, which is due to the location of their catchment areas. The watersheds of only two rivers — Dzhida and Orongoy — are located entirely in the Selenga midlands. Most of the catchments of the Selenga and Chikoy rivers are located outside the study area. This circumstance determines to a large extent the good consistency of long-term changes in the water flows of these rivers and the differences from the river flow regime. Orongoya and especially r. Jids. The dynamics of the width of the annual rings of Scots pine trees growing in the Selenga midlands reflects changes in its hydrothermal regime during the current and previous growing seasons. The influence of atmospheric precipitation is pronounced, so the amount of precipitation for May–June explains about 40% of the increase for the residual (without autocorrelation component) tree-ring chronology.