ИСТИНА

Groundwater recharge by precipitation is the main source of groundwater natural resources, which are widely used for human needs in European part of Russia. The climate conditions change from semi-arid in the south to humid and boreal in the north of the investigated region. The main goal of the presented studies is to analyze the effect of observed climate changes in different climate regions on the processes of groundwater recharge. Meteorological data of 20 weather stations, located from south to north of the investigated region for previous (1965-1988) and modern (1989-2019) periods were compared and show different latitudinal changes in annual and seasonal averages of precipitation, wind speed, air temperature and humidity. Program code Surfbal was used to simulate surface runoff, evaporation and seepage to the soil based on daily meteorological data for 1965-2019 taking into account snow accumulation and melting, as well as soil freezing and thawing processes. Simulation results verified by observed annual and intra-annual variations of snow and freezing depths. Well known program Hydrus 1D with daily seepage, potential evaporation and transpiration values from Surfbal as input data was used to simulate unsaturated flow in vadose zone, plant transpiration and groundwater recharge. Modeling was carried out based on average soil and vegetation parameters, typical for the investigated region. Differences in annual and seasonal averages of surface runoff, soil evaporation, transpiration and groundwater recharge for previous (1965-1988) and modern (1989-2019) periods were obtained as a result of simulations and were correlated to corresponding differences in climatic characteristics. A comparative analysis of differences in climatic and water-balance annual and seasonal characteristics for the previous and modern periods showed the following main results. Annual surface runoff slightly decrease in the southern and slightly increase in northern regions and these changes best correlated with annual precipitation changes. However, changes in runoff intra-annual hydrograph are more significant and shows decreasing of spring high water and increasing of winter runoff due to increase of winter air temperature. Despite the general increase in air temperature, there are no obvious changes in the annual total evaporation due to a general decrease in surface wind speed. In the southern regions, there is no climate changes in the annual groundwater recharge, while in the central and northern regions recharge increase to 60 mm/year due to the observed increase in temperature and precipitation in winter and a decrease in the depth of freezing.