Any middle-aged or elderly Israel could reminisce about how the Dead Sea used to be much larger with rounded coasts and without any sinkholes. The Dead Sea is shrinking, and there are many reasons for this – climate change and human overuse of water as a resource.
The sinking water level has a number of dangerous consequences, including fresh groundwater flowing downstream causing salts to dissolve in the soil and producing those sinkholes. But it also leads to large-scale subsidence of the surrounding land (the sudden sinking or gradual downward settling of the ground’s surface with little or no horizontal motion).
Researchers from an interdisciplinary team of several sections from the GFZ German Research Centre for Geosciences, together with colleagues from Hannover, Kiel and Padua, have now for the first time demonstrated a direct link between the decrease in the water table, evaporation and land subsidence. They report on this in the journal Scientific Reports under the title “Delayed subsidence of the Dead Sea shore due to hydro-meteorological changes.”
The team used a wide range of instruments, from measurement methods based on the Global Navigation Satellite System (GNSS) to radar satellites and on-site gauge and climate stations. The researchers showed that the solid earth moves up and down synchronously with fluctuations in the water surface and groundwater level with a time lag of about eight weeks, but the trend is clearly in one direction – downward.
The Dead Sea’s water level decreases about one meter per year, and the land sinks about 15 centimeters per year. Inflows from rainfall in the surrounding mountains and the Jordan River cause short-term rises in the lake level. However, water withdrawals from the tributaries for agriculture, pumping of saline water to extract potassium and evaporation in the high heat turn the balance permanently negative.
The rapid decline of the Dead Sea leads to both short- and medium-term climatic changes and natural hazards that pose a major challenge to local communities, they wrote. Changes in precipitation and evaporation cause major flooding events, desertification and land degradation. The retreat of the salt-water to fresh-water transition zone at the Dead Sea shore results in an increasing groundwater gradient. “Both developments have led to dissolution and erosion processes of the sediments, evaporates (salt) and other soluble material on both sides of the Dead Sea.”
The dangerous combination of land subsidence to the sinking water table has long been clear, the researchers continued, but the fact that the movement of the land surface is so directly related to hydro-meteorological fluctuations is new. The researchers determined this connection within an observation period of three years. For agriculture, tourism and infrastructure in the region, land subsidence and water loss are very threatening. The measurements show for the first time how closely land, water and atmosphere are linked.