Thermodynamic constraints on Dead Sea evaporation: can the Dead Sea dry up?

Abstract

The relation between climatic parameters (relative air humidity) and the water activity of the Dead Sea water determines the possible maximum evaporation of the lake. Using the Pitzer thermodynamic approach, the activity of the Dead Sea water during evaporation was calculated and compared to the present relative air humidity above the water. Long-term (1992–1997) quasi-continuous meteorological data acquired at sea provide detailed information on the patterns and trends of the relative humidity above the lake. Present climatic conditions allow the Dead Sea water to evaporate down to a water activity of 0.50, corresponding to the lowest air humidity measured over the lake. This water activity falls in the range of halite precipitation, while carnallite precipitation starts somewhat lower ( a H 2O =0.49). Our dynamic model predicts that for air humidity as low as 50% (reflecting present climate conditions), the Dead Sea level may drop to as low as −500 m (i.e., 500 m below mean sea level). At that point, the lake will have a volume of 88 km 3 and a surface area of 526 km 2. For the sake of comparison, at the beginning of 1977, after the southern basin of the Dead Sea was separated from the northern basin, the level of the lake was −402 m, its volume was 146 km 3, and its surface area was 815 km 2.