As the main freshwater resource on Earth's surface, lakes play an important role in maintaining ecosystem stability and the sustainable development of human society.
However, it's been difficult to evaluate changes in global lake-water volume across space and time due to data problems. Specifically, ground-monitoring data have not been sufficiently representative of all lakes, and traditional radar altimetry satellites have only provided data on a few large lakes.
Recently, a research group led by Prof. SONG Chunqiao from the Nanjing Institute of Geography and Limnology of the Chinese Academy of Sciences conducted a quantitative study of lake-water level and volume. The researchers used satellite laser altimetry to study natural lakes over 10 km2 in area during the period from 2003 to 2020.
Their findings were published in Geophysical Research Letters.
In the study, the researchers combined laser altimetry information from two satellites, ICESat and ICESat-2, to compile a long-term time series of lake-water level data. They also analyzed spatial patterns of hydrological change in lakes around the world since the early 21st century.
The results showed that the two satellites could monitor variations in the level and volume of about 6,500 lakes (each >10 km2). The total water volume in the observed lakes accounted for 94% of the total water volume of global lakes.
About 54% of the lakes showed a significant trend in water-level change from 2003 to 2020, with 80% showing an upward trend. As a result, the total water volume of the observed lakes increased at a rate of 10.88 ±16.45 Gt (109 t)/yr from 2003 to 2020.
By using a lake-area weighting method to extrapolate data from observed lakes to unobserved lakes in the same basin, the scientists estimated a global rate of change in lake-water volume of 16.12±20.41 Gt/yr for the study period based on about 14,700 natural lakes larger than 10 km2.
"The inner Tibetan Plateau in Asia, the Great Lakes region in North America, the Great Rift Valley in East Africa, northern Europe, and the Amazon are typical regions showing significant increases in lake volume. The total increase of water volume in these five areas accounts for 60% of the total water volume in the observed lakes," said Prof. SONG.
Although the water level of most of the world's lakes increased by different degrees during the study period, many lakes in arid/semi-arid and high water-stress regions still showed significant water-level decline and severe water loss.
"As the climate continues to warm and the water demand for social and economic development increases in the future, these shrinking lakes will become even drier without further protection policies and actions," said LUO Shuangxiao, first author of the study.
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