A research article on global hydrology published in Science on the 18th of May shows that more than half of the large freshwater lakes across the world experienced a decline in storage between 1992 and 2020. The natural volume of the world’s lakes has declined by some 26 Gigatonnes per year (equivalent to the volume of some 10 million Olympic sized swimming pools) over these three decades. The article notes that it is already well known that the combination of human activity and climate change are affecting the world’s surface water, of which 87% is stored in lakes. A number of scientific studies that have been published in the past decade have pointed to this fact, with individual stories such as the decline of the Aral Sea, the Caspian Sea, the Great Lakes and Lake Poyang having been documented also.
However, although those studies noted the decline, they were not able to tease out the causes of this decline with certainty, largely because of limitations in modelling and observation, such as limited spatial coverage of data. With the use of satellite data, however, it is possible to pan out and look at large scale changes in lake water storage, as well as document changes over a long time period. Using recently developed algorithms and statistical learning frameworks that factor in the impacts of human activity and climate data, the researchers show that some 56% of the changes in storage over time is directly attributable to human activities and changes on temperature and evaporation.
Across the world, a total of 457 natural lakes (43% of the total number of lakes studied) had significant water losses with a total loss of 38 Gigatonnes per year. By contrast, 234 natural lakes experienced storage gains with a total of 13 Gigatonnes per year.
The largest losses were geographically concentrated: over 80% of the total decline in drying lakes stems from the 26 largest losses. The largest inland water body, the Caspian Sea, accounts for 49% of the total decline and 71% of the net decline in natural lake volume. Similarly, the Aral Sea is losing 6.59 Gigatonnes of water per year, Lake Mar Chiquita is losing 0.75 Gigatonnes per year, and the Dead Sea is losing some 0.6 Gigatonnes per year.