The largest lake in the world, on the way to desiccation

One of the greatest environmental catastrophes of the 20th century was the virtual disappearance of the Aral Sea.

The 21st century may be the drying up of the largest lake on the planet.

A group of scientists warn that the Caspian could lose up to a third of its surface in the remainder of a century.

In the first case, the origin of the disaster was a wild agrarian policy of the former Soviet Union and the successor republics.

In the second, it is climate change that is evaporating more water than it comes from rivers.

The Caspian, one of the natural borders between Asia and Europe, has been losing water since the 1970s. The rate of decline, however, was one or two centimeters a year.

It seemed an acceptable loss in a huge lake of 371,000 km², an area equivalent to 3/4 of the surface of Spain.

But a group of Dutch and German researchers have found that the rate of drying has accelerated to six or seven centimeters a year and will do so even more in the coming decades.

"Our model predicts a drop in sea level in the Caspian of nine meters in an intermediate [CO₂] emissions scenario and 18 meters in a high emissions scenario by the end of the century," says the researcher from the University of Bremen ( Germany) and co-author of this study on the evolution of this salt lake Matthias Prange.

Measured in desiccated area, in the first case, the Caspian would lose 23% of its study surface.

In the second, the most probable if the Paris Agreements on climate change are not fulfilled, 34% of this sea would disappear.

Caspian water depends on three main factors: The Volga River contributes 90% of its water volume.

Another significant contribution is that of winter rainfall.

On the other side of the balance are evaporative losses when you press the thermometer.

Of the three, it is temperature that is changing, the study, published in the scientific journal

Communications Earth and Environment, shows

.

"In the case of the Caspian Sea, the effect of evaporation is by far the most important," says Prange.

In fact, everything indicates that winter rainfall in the northern part of the Volga basin will increase.

“Therefore, the river runoff and its discharge into the Caspian Sea may increase slightly in the future.

However, the greater effect of evaporation from the lake will lead to the projected decrease in sea level ”, he completes.

An apparently paradoxical phenomenon occurs here: while the warming is causing an increase in the level in the oceans, that of the inland seas and large lakes will fall due to the same effect of the rise in temperatures.

In addition to losing a third of its surface, the rest of the Caspian will support very low levels of oxygen

The authors do not believe that the Aral and Caspian situations are comparable.

The first, of which less than 10% remains and fragmented into two small unviable seas, is doomed.

The second would still have, in the worst case, 66% of its area and with depths reaching up to 1,000 meters.

But the loss of just a third can make it a dead sea from a biological point of view.

"At first, it will not mean much for the deeper areas, but, in the end, the drop in sea level will cause three effects that could trigger anoxia [lack of oxygen] also in the depths", warns the geologist from Utrecht University (Netherlands) and study co-author Frank Wesselingh.

The less available ice and the oxygen it contains, the excessive concentration of nutrients provided by rivers, and rising temperatures “create the perfect conditions to deprive the deeper Caspian areas of oxygen levels (already low in by itself) and could end all life, "he concludes.

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