An almost unimaginable regime change has taken place in the natural world, reflecting the vast and growing dominance of humanity over one of the most vital resources of our planet: fresh water.
According to the researchers, this is the first global study of the human impact on the water cycle, scientists used NASA satellite measurements to remotely quantify changes in water levels in a staggering number of water bodies: 227,386 in ponds, lakes and reservoirs, small or large.
While man-made reservoirs, such as man-made dams, comprise only 3.9% of this gigantic planetary surface water storage system, this small fraction masks an astonishing truth about how much it really controls humanity. on freshwater fluctuations.
When calculating the amount of global change in water levels in both natural and man-made systems, it appears that man-controlled reservoirs account for 57% of all surface water variability – more than half of the flow and flow. reflux from freshwater systems.
“We tend to think of the water cycle as a purely natural system: rain and melting snow end up in rivers, which go to the ocean, where evaporation begins the whole cycle again,” explains geophysicist Sarah Cooley of Stanford University.
“But humans actually intervene substantially in this cycle. Our work demonstrates that humans are responsible for most of the seasonal variability in surface water storage on Earth.”
The results, extracted from 22 months of data collected by NASA, Ice, Cloud and Land Elevation Satellite 2 (ICESat-2), provide a unique snapshot of water storage around the globe, capturing and measuring water bodies as small as possible. football in the survey.
“Previous satellites have failed to come close to that,” says Cooley, “but although the scientific findings are admirable, they are not available.”
“There are a lot of ways this is bad for the environment.”
Risks range from negative effects on natural ecosystems due to water scarcity to the spectrum of greenhouse gas emissions from artificial reservoirs.
Of course, there are other positive aspects of man-made tanks: beyond the simple control of water supply, they allow things like hydropower systems, while dams can also provide protection against floods.
However, the awareness that we have taken the majority control over something as natural as the flow and ebb of fresh water is a troubling discovery.
Another powerful reminder of the effect that our species has on the environment around us – with consequences so impossible to magnify, that we can only hope to see them from space.
“Of all the volume changes in freshwater bodies on the planet – all the floods, drought and melting snow that push lake levels up and down – humans have taken over almost 60% of this variability,” says the environmental scientist. Laurence Smith of Brown University.
“This is a tremendous influence on the water cycle. In terms of human impact on the planet, this is right up there, with impacts on land cover and atmospheric chemistry.”
The findings are reported in The nature.