Purpose. When discussing the Sea of Azov salinization both in the 1970s and in the current period, the reduction of river runoff (primarily in the Don River) is indicated as the main reason for this phenomenon that results in the increased advection of the Black Sea waters. However, this factor alone is not enough to explain salinity decrease in the last quarter of the 20th century as well as its rapid growth in 2007–2020. The paper is purposed at assessing the contribution of water balance components to the change in the Azov Sea salinity for more than 50 years (1966–2020).

Methods and Results. A mathematical model of water-salt balance is used to assess the annual average salinity of the Sea of Azov. The variability of all the water balance components and the sources of its uncertainty are considered. It is shown that the model applied is resistant to variation of the input data. Based on the correlation analysis, it is found that during the salinization period, evaporation plays an important role along with the river runoff. At that in the 1970s, a decisive impact upon evaporation was exerted by the wind speed, whereas at the beginning of the 21st century – by the temperature and humidity regimes.

Conclusions. At the beginning of the 21st century, the reason for rapid salinity increase in the Azov Sea waters consisted in the prolonged period of low-water in rivers coinciding with the period of high water and air temperatures that resulted in an increase of evaporation from the sea surface. The obtained results permit to conclude that at the changed atmospheric processes in the region, the only factor consisting in transition from the low river inflows to the Azov Sea basin to the high ones may be not enough to provide significant decrease of seawater salinity. This circumstance should be taken into account when preparing the plans for adapting the economic activities to the climate changes.