Changes in the rate of evaporation from the dead sea



Heat balance calculations indicate that during the last 40 years a marked decrease in the evaporation rate from the Dead Sea has accompanied its increased salinity. Two-thirds of the estimated 17 per cent decrease is attributed to the reduced vapour pressure of its now salt-saturated waters, the remaining one-third to the reduction in radiation balance caused by the greater longwave loss from its warmer sea surface. The rate of evaporation from a hypothetical Dead Sea with a surface level restored to previous levels by an influx of Mediterranean waters was estimated to be 158 per cent of its current rate, which is 1.05 m per year. Two-thirds of this increase was attributed to the greater vapour pressure gradient between the less saline surface water and the atmosphere, one-third to the increased radiation balance at its cooler sea surface. Although the mechanism for these changes are well understood and easily calculated, a number of complex interactions exist between the various effects that do not allow a quantitative relationship to be established analytically between the Dead Sea's surface level or salinity and rate of evaporation. However, empirically, the linear relationship between annual evaporation, E (m year−1), and surface density, D (g cm−3), E = 4.701 - 2.926 D. accounts for 98 per cent of the variation between evaporation from a salt-free and from a salt-saturated Dead Sea.