Human impact on Earth's freshwater resources revealed

Human impact on Earth’s freshwater resources revealed Today’s Video of the Day from NASA Goddard reveals the surprising influence that humans have on Earth’s freshwater resources.

In the first study to assess seasonal variability in water bodies worldwide, researchers have discovered that water levels in human-managed reservoirs fluctuate about four times more compared to natural lakes and ponds. 

“We tend to think of the water cycle as a purely natural system: Rain and snowmelt run into rivers, which run to the ocean where evaporation starts the whole cycle again,” said study lead author Sarah Cooley of Brown University. “But humans are actually intervening substantially in that cycle. Our work demonstrates that humans are responsible for a majority of the seasonal surface water storage variability on Earth.”

The study was focused on data from NASA’s Ice, Cloud and Land Elevation Satellite (ICESat-2). The primary goal of the ICESat-2 mission is to track changes in the thickness and elevation of ice sheets around the world. The measurements are obtained using a laser altimeter, and elevation is calculated to an accuracy of 25 millimeters. 

The satellite measured seasonal water levels in more than 227,000 lakes, ponds, and reservoirs worldwide from October 2018 to July 2020. The water bodies ranged in size from the American Great Lakes to ponds with areas less than one tenth of a square mile. 

The study revealed that while natural lakes and ponds varied seasonally by an average of .22 meters, human-managed reservoirs varied by .86 meters. This means that, when compared to natural lakes, reservoirs account for 57 percent of the total variation. 

Human influence on freshwater resources was found to beP even stronger in arid regions like the Middle East, American West, India and Southern Africa, where seasonal variability attributed to human activity exceeds 90 percent.

“Of all the volume changes in freshwater bodies around the planet – all the floods, droughts and snowmelt that push lake levels up and down – humans have commandeered almost 60% of that variability,” said study co-author Professor Laurence Smith.

“That’s 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.”

Video Credit: NASA Goddard

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By Chrissy Sexton, Earth.com Staff Writer