Variability in spatial–temporal recharge under the observed and projected climate: A site-specific simulation in the black soil region of Russia

•Groundwater recharge was studied at 3 sites with various landscapes and soil profiles.•Recharge was evaluated by numerical simulations of surface and subsurface water budget.•Results of historical simulation did not reveal any traces of climate change in recharge.•The projected simulation showed that recharge would decrease at the end of 21 century.•The weakness of recharge predictions depends on the uncertainty of climate forecasts. The main purpose of this work is to evaluate diffuse groundwater recharge and its temporal dynamics at sites with different landscapes and soil profiles under observed and projected climate variability. Three typical sites with different landscapes and topsoil profiles were chosen for the field study. Field work consisted of pit development and soil sample collection for laboratory study using the centrifuge method. Soil hydraulic parameters were obtained by the RETC code using the observed values of volumetric water content vs. pressure head. HYDRUS-1D code was used to estimate groundwater recharge based on a 70-year (1945–2015) meteorological dataset with daily resolution (including values of precipitation, air temperature, wind speed, and humidity). This dataset was preprocessed using our SURFBAL code to calculate the surface and topsoil water and energy balance. Retrospective historical simulation results showed that there was a considerable variation in the mean annual groundwater recharge values (49–104 mm/year) for the three studied profiles. The temporal change in groundwater recharge occurred relatively synchronously at all sites and was governed by the change in the current annual aridity index. The results of this historical simulation did not reveal any traces of climate change in the groundwater recharge of the studied region in the last 30–40 years. To predict the recharge variations in the second half of the 21st century, the LARSWG forecast weather generator with the climate projections of the 5th General Circulation Models (GCMs) from the Coupled Model Intercomparison Project 5 (CMIP5) family was used. On average in the case of climate development under the maximum greenhouse gas emissions RCP8.5 scenario, there will be a reduction in groundwater recharge in the studied region in 2060–2080, caused by two factors: change of aridity index, which determines evapotranspiration during a warm season and the accumulation of snow and subsequent meltwater infiltration during the snowmelt periods.