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A regime shift of almost unimaginable magnitude has taken place 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 world’s first survey of human impacts on the water cycle, scientists have used satellite measurements from NASA to remotely quantify water level changes in an impressive number of planes of water: 227,386 from the world’s ponds, lakes and lakes. tanks, whether small or large.
While human-managed reservoirs such as man-made dams make up only 3.9% of this giant planetary surface-level water storage system, this tiny fraction masks a bewildering truth about the control that the humanity actually exerts on the fluctuations of fresh water.
When the amount of global change in water levels in natural and human-managed systems is calculated, it turns out that human-controlled reservoirs account for 57% of all surface water variability – over half of all ebb and flow in freshwater systems.
“We tend to think of the water cycle as a purely natural system: rain and snowmelt flow into rivers, which flow into the ocean where evaporation starts all over again”, explains the geophysicist Sarah Cooley from Stanford University.
“But humans are in fact substantially involved in this cycle. Our work shows that humans are responsible for most of the seasonal variability in surface water storage on Earth.”
The findings, gleaned from 22 months of data collected by NASA’s Ice, Cloud and Land Elevation Satellite 2 (ICESat-2), provide a unique insight into water storage in the world, capturing and measuring water bodies as small as a football field as part of the survey.
“Previous satellites haven’t been able to come close to this,” Cooley says, but while the scientific achievements are admirable, the take-out is 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 specter of greenhouse gas emissions from artificial reservoirs.
Of course, human-managed reservoirs have other advantages as well: beyond just controlling the water supply, they allow things like hydroelectric systems, while dams can also offer protection against water. floods.
Yet 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 the effect our species has on the environment around us – with consequences so incredibly large we can only hope to see them from space.
“Of all the changes in volume in freshwater bodies around the planet – all the floods, droughts and snowmelt that cause lake levels to rise and fall – humans have requisitioned almost 60% of this. variability, ”says Laurence Smith, environmental scientist, Brown University.
“It’s a huge influence on the water cycle. In terms of human impact on the planet, it’s right up there with impacts on land cover and atmospheric chemistry.”
The results are reported in Nature.
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