Will the Dead Sea Die?
Photograph of the western shore of the Dead Sea in 2019 showing retreating shorelines. In the twentieth century the water used to cover this entire beach, which is about one kilometer wide now.
Will the Dead Sea Die? That was the title of an article published in 1998 in the scientific journal Geology by a friend and colleague of mine, Yoseph Yecchieli. Yossi is a hydrogeologist like me, and has worked for decades for the Geological Survey of Israel. In my visit to Israel in the year 2000 he showed me around the western shores of the Dead Sea at the time, where sinkholes were opening due to subsurface dissolution of salt beds. The cause was fresh groundwater encroaching toward the Sea as its shoreline receded and level dropped. Tourist hotels at the Sea were no longer at the shore line, and were in danger from sinkholes. At that point in time the lake level was dropping at nearly 1 meter per year. Thus, the question presented itself—how long will this continue into the future? Will the Dead Sea go the way of the Aral Sea? The latter, situated at the southern border of Kazakhstan in central Asia, used to be the fifth largest freshwater lake in the world. But due to diversions of its river input to agriculture and human consumption, the Aral Sea is now only about 10% of its original extent. This drying up has been called the worst environmental disaster in human history. Will the Dead Sea also dry up like this? In last week’s blog I discussed the history of the Dead Sea and how humans have benefited from its resources. This week I will discuss the future of the Dead Sea and if it will survive the current human demand for water resources.
The Dead Sea's problem is its water budget. We use water budgets all the time in hydrology to make calculations. It is based on the principle of mass (or water) conservation; mass cannot be created or destroyed out of nothing. It might change form such as in the melting of snow or evaporation to water vapor, but the molecules do not change from being H2O under natural settings. Thus, if you take the difference between the amount of water entering a lake and leaving it, the result must be the change in the lake's volume. If more is leaving than entering, the lake level will go down. Early in the twentieth century the Dead Sea was in balance—the amount of water entering was equal to the amount leaving. There is no surface water outlet for the Dead Sea. Water leaves only by evaporation, and its valley is hot and dry, so the evaporation rate is quite high. As time progressed Jordan and Israel both began to draw off more and more water from the Jordan River—the Sea’s main inflow of water. Lower inflow was not matched by lower evaporation, and so the water level began to fall. You can imagine if the inflow is cut off all together that eventually the Dead Sea would dry up completely, like the Aral Sea has almost done. Or would it?
The Dead Sea has one important difference from the Aral Sea. The Dead Sea is salty—very salty. Evaporation from the surface of a water body is driven in part by the fraction of its liquid that is water. Usually that is close to 100 percent, but the Dead Sea is saltier than ocean water by a factor of about ten. This results in Dead Sea brine being only about 70% water. And as the Dead Sea is shrinking its salinity is increasing, and the brine's water content is going even lower, reducing the evaporation rate. The other limiting factor for evaporation is the humidity in the air. The atmosphere has humidity that will try to recondense constantly on a water body’s surface. Air with 100% humidity cannot evaporate any water, and with 70% humidity can only evaporate a liquid brine with 70% water content or more. At some point in the future, according to Yecchieli, a new equilibrium will be reached when the salinity is high enough. At that point, the the water content of the brine will drop below 50% and the evaporation rate will match the average humidity there in the atmosphere. At that point the Dead Sea level should be about 100 meters lower than it was in 1998. That will certainly cause a lot more retreat of the shoreline—and continue to aggravate the tourism industry. The Dead Sea is much deeper than 100 meters though, and so the final surface area is predicted to be about 80% of that of today. Fortunately, in the end the Dead’s Sea’s high salinity should save it from extinction.