A dynamic model of the Aral Sea water and salt balance

The Aral Sea is shrinking rapidly since the 1960s mainly because of the diversion of the Amu Darya and Syr Darya rivers for irrigation purposes. Since then, the evaporation became the most important component of the water balance of the Sea and led to a concentration of the remaining salts. In this article, we investigate through a coupled mathematical model of water and salt balance of the Aral Sea, the dynamic evolution of the sea. The water balance considers river inflow, groundwater inflow, atmospheric precipitation and evaporation. The salt balance considers the dominant ions and the chemical precipitation of gypsum, epsomite and mirabilite. The evaporation rates are calculated with a modified Penman equation accounting for the salinity of the lake and using statistical climatic data. With this model, we obtain an estimate of the evaporation flux (between 1100 and more than 1200 mm/year depending on the salinity) larger than earlier estimates. The estimated groundwater discharge into the sea is also larger than earlier estimates and is highly variable from year to year. The last point is that the model is able to simulate rather well the evolution of the salinity until the 1980s, but it does not reproduce accurately the chemical evolution of the lake during the most recent period and needs further improvements.