In addition to growing algal blooms and oxygen depletion, a new study finds that Earth’s freshwater bodies are draining at an accelerated rate.
Moreover, lake evaporation has a higher impact in the hydrological cycle than previously believed, according to Texas A&M University researcher Gang Zhao. This mechanism has significant implications for our climate and weather models.
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Approximately 5 million square kilometres of the Earth’s surface are covered by lakes, both natural and manmade. They contain about 90 percent of the fresh liquid surface water on our globe and are teeming with diverse species.
However, increasing temperatures and sun radiation as a result of variations in cloud cover have made the sky thirstier than ever. Due to a reduction in ice cover, larger regions of uncovered water have allowed the sky greater access to these water molecules. All of these variables contribute to the acceleration of the water cycle, from its pooling on land to its dispersion in the atmosphere.
Earlier estimates of this water transfer relied on evaporation rates, but these alone do not adequately represent the volume of lake water that is being lost due to other dynamics such as freeze-thaw cycles. Due to this dependence on localised climatic factors, an accurate evaporation measurement must be independently calculated for each lake.
Therefore, Zhao and his colleagues did so for an astounding 1.42 million lakes worldwide. They used satellite data on monthly water loss from 1985 to 2018 and accounted for variations in evaporation rate, surface area, ice duration, and heat storage for each of these lakes.
“We found that the long-term lake evaporation is 1,500 plus or minus 150 cubic kilometers per year, which is 15.4 percent larger than previous estimates,” says Zhao.
And the sky is drinking over 3 trillion liters more than previously each year. The researchers also found artificial reservoirs have a proportionally larger contribution to this evaporation (16 percent) than their storage capacity of 5 percent would suggest.
“From a global perspective, the total reservoir evaporation can be larger than the combined use of domestic and industrial water,” explains environmental engineer Huilin Gao.
“However, even in the United States, very few lakes/reservoirs have reliable evaporation data.”
Zhao and team made the dataset they created, the global lake evaporation volume (GLEV), publicly available and urge those making water management decisions and the wider scientific community to make use of it.
“With results for individual water bodies, GLEV can really help improve reservoir management decision-making all over the world, especially under increasing drought events and population growth,” says Gao.
“This dataset helps the science community better understand the role that these water bodies play in Earth systems, from global weather forecasting, flood and drought modeling to Earth system modeling under climate change.”