Evaporation from the hypersaline Aral Sea in Central Asia

The Aral Sea, once the world's fourth largest lake, has shrunk by 91 % in area and 95 % in volume since 1960s. The shrinkage has resulted in a notable increase in water salinity, which may affect the surface evaporation. Despite previous studies, the hydrological consequences of salinity in the Aral Sea have often been overlooked. In this study, we investigated the impact of water surface salinity on evaporation by employing a water activity-based Penman salinity equation, and we explored its effects on the water balance of the Aral Sea. We established an empirical relationship between the water activity and water salinity. The results indicated that the evaporation rates were overestimated when salinity effects were excluded from evaporation estimations in Aral Sea, especially for the hypersaline South Aral Sea. During the period from 2000 to 2020, the evaporation of a 16 km³ water volume could have been overestimated if the salinity effects were ignored. When calculated from updated evaporation and the lake water balance, the inflow from the middle reaches to the Aral Sea showed significant deviations from the existing data sources. We emphasize that, the observed runoff at stations is higher than our estimated inflow.