Humans now control most of all freshwater fluctuations on Earth’s surface

There has been a regime change on an almost unimaginable scale in the natural world, reflecting humanity’s vast and growing dominance over one of our planet’s most vital resources: fresh water.

In what researchers say is the first global study of human impacts on the water cycle, scientists have used measurements from NASA satellites to remotely quantify changes in the level of water contained in a quantity staggering bodies of water: 227,386 of ponds, lakes and reservoirs, whether small or large.

While human-managed reservoirs such as artificial dams comprise only 3.9 percent of this giant, planetary-scale surface-level water storage system, that tiny fraction masks a mind-boggling truth about how much control humanity actually exercises. on fluctuations in fresh water.

When you calculate the amount of overall change in water levels in natural and human-managed systems, it turns out that human-controlled reservoirs account for 57 percent of all surface water variability, more than half of all flow. and backflow in freshwater systems.

“We tend to think of the water cycle as a purely natural system: rain and snowmelt run into rivers, which run into the ocean, where evaporation starts the cycle again,” explains geophysicist Sarah Cooley of the University of Stanford.

“But humans are actually substantially intervening in that cycle. Our work shows that humans are responsible for most of the seasonal variability of surface water storage on Earth.”

The results, drawn from 22 months of data collected by NASA’s Ice, Cloud and Land Elevation Satellite 2 (ICESat-2), provide a one-of-a-kind snapshot of water storage around the world, capturing and measuring such small bodies of water. like a soccer field within the survey.

“Previous satellites have not been able to come close to that,” says Cooley, but while the scientific achievements are admirable, the conclusions are not.

“There are many ways this is bad for the environment.”

The risks range from negative effects on natural ecosystems due to water scarcity, to the spectrum of greenhouse gas emissions emanating from man-made reservoirs.

Of course, there are other positives to human-managed reservoirs as well: beyond just controlling the water supply, they enable things like hydroelectric systems, while dams can also offer flood protection.

Still, the realization that we have assumed majority control over something as natural as the ebb and flow of fresh water is a disturbing discovery.

Another stark reminder of how much of an effect our species has on the environment around us, with consequences so incredibly great that we can only hope to see them from space.

“Of all the volume changes in freshwater bodies around the planet, all the floods, droughts and thaws that push lake levels up and down, humans have taken over almost 60 percent of that variability, “says environmental scientist Laurence Smith of Brown University.

“That’s a tremendous influence on the water cycle. In terms of human impact on the planet, this is on par with the impacts on land cover and atmospheric chemistry.”

Findings are reported in Nature.


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