Estimates of probable change in water balance parameters of the Black and Azov Seas drainage basin under the global warming by 1°C were obtained. A steady-state hydrological model has been developed for evaluation of river runoff and evaporation. The paleoclimatic reconstruction for global warming on 1°C has been used as empirical scenario. This scale of climate change corresponds to the warm epoch of the past, considered as an analogue of the future climate: the Holocene Thermal Maximum (7-6 ka BP). The estimates indicate possible increase in the total river inflow into the Black and Azov Seas by about 17 km3 per year and increase of the mean annual evaporation by 27 mm per year relative to the period of 1961-1990 years. Estimation was made notwithstanding water consumption.