The largest lake in the world is drying up | Science

The largest lake in the world is drying up |  Science

One of the greatest environmental disasters of the twentieth century was the virtual disappearance of the Aral Sea. The 21st century may well be the drought of the largest lake on the planet. A group of scientists has warned that the Caspian Sea 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 the unbridled agricultural policy of the former Soviet Union and its successor republics. In the second case, climate change is causing more water to evaporate than to rivers.

The Caspian Sea, one of the natural borders between Asia and Europe, has been losing water since the 1970s, but the rate of decline has been a centimeter or two per year. It seemed an acceptable loss in a huge lake of 371,000 square kilometers, about 3/4 the size of Spain. But a group of Dutch and German researchers have concluded that the rate of dehydration has accelerated to six or seven centimeters per year, and it will do so even more in the coming decades.

Our model predicts a sea level drop in the Caspian Sea of ​​nine meters in an emissions scenario. [de CO₂] Average and 18 meters in one of the highest emissions by the end of the century “, says researcher at the University of Bremen (Germany) and co-author of this study on the evolution of this salt lake, Matthias Prang. When measuring in a dry area, in the first case, the Caspian Sea will be lost 23% of its study surface In the second, most likely if the Paris agreements on climate change are not fulfilled, 34% of that sea will disappear.

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The waters of the Caspian Sea depend on three main factors: the Volga River contributes 90% of its water volume. Another important contribution is the winter precipitation. On the other side of the scale there are evaporation losses when the thermometer is pressed. Of the three, what changes is the temperature, as they show in the study published in the scientific journal Earth and Environment Communications.

“In the case of the Caspian Sea, the effect of evaporation is by far the most important,” says Prang. Indeed, everything indicates that the winter precipitation in the northern part of the Volga Basin will increase. Therefore, the flow of the river and its discharge into the Caspian Sea may increase slightly in the future. However, the greater impact of evaporation from the lake will lead to the expected decrease in sea level, “he continues.

A paradoxical phenomenon appears to be occurring here: as warming causes the oceans to increase, inland seas and large lakes will decrease due to the same effect as higher temperatures.

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

The authors do not believe that the two situations of Aral and Caspian are the same. The first, which has left less than 10% and crumbled into two unviable small seas, is doomed to perish. The second will remain at worst 66% of its area and depths of up to 1,000 meters. But losing just a third could make it a dead sea from a biological point of view.

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“ At first it wouldn’t mean much for the deeper regions, but in the end, lower sea levels would have three effects that could lead to hypoxia. [ausencia de oxígeno] Also in the depths, ”warns geologist at Utrecht University (the 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“ creates ideal conditions for depriving deep regions of the Caspian Sea of ​​oxygen levels (Really low on its own) It can end all life. “

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