La Jornada – “The human being has a dominant role in the water cycle”

Madrid. The first global account of fluctuations in lakes and reservoirs showed that 57 percent of the variance occurs in reservoirs clogged by dams and other artificial water bodies.

This finding highlights the dominant role humans now play in the Earth’s water cycle, according to the study published in the journal. Temperate nature.

Water levels in human-managed ponds, lakes and reservoirs rise and fall from season to season, but until now it has been difficult to analyze exactly how much this difference they cause compared to natural cycles. Analysis of new satellite data shows that 57 percent of the seasonal variation in storage of Earth’s surface water now occurs in reservoirs clogged with dams and other artificial water bodies.

“Humans have a dominant influence on the Earth’s water cycle,” says lead author Sarah Cowley, a postdoctoral researcher at Stanford University’s School of Earth, Energy and Environmental Sciences.

Scientists used the data collected at 22 months by Icesat-2 From NASA, which launched in October 2018 and collected high-resolution measurements of 227,386 water bodies around the world, including some smaller than a soccer field.

“ Previous satellites weren’t able to get close to that. ” Cooley, who did most of the analyzes on a laptop in his parents’ living room after coronavirus restrictions canceled his scheduled field season in Greenland, said he needed to find a project he could work on remotely .

Cole and colleagues found that water levels in lakes and ponds change by about 22 cm between rainy and drought seasons. Meanwhile, human-managed reservoirs fluctuate nearly four times this amount, rising and falling 800 meters from season to season.

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The western United States, South Africa and the Middle East are among the regions with the highest diversity of reservoirs, with an average of 2-4 meters. They also have one of the strongest human impacts, with managed reservoirs accounting for 99 percent or more of the seasonal variations in surface water storage.

“This is an indication that these places are under water stress where careful water management is really important,” said Cooley. In some other watersheds, humans account for less than 10 percent of the variability.

“Sometimes these basins are side by side because even within the same area, a combination of economic and environmental factors means that people make different decisions about how to manage the storage of surface water,” he added.

While water levels naturally rise and fall throughout the year, this seasonal variation is exaggerated in reservoirs fortified with dams where more water is stored in the rainy season and diverted when it dries up.

“There are many ways that harm the environment,” Cole said, from destroying fish populations to potential increases in methane emissions from greenhouse gases.

However, the implications for regulating water levels in the reservoirs are not black and white. Much of this disparity is related to hydroelectric production or irrigation. It can also protect from flooding, “Cooley said.

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