Scientists looked at more than 200,000 bodies of water from space. This is why 

Researchers have used NASA satellite data to examine 227,386 bodies of water to understand more about the extent of human influence on the global hydrological cycle.

Such research is "essential for the sustainability of freshwater resources on Earth", the scientists involved say in introducing their research.

Their most striking finding? Humans are responsible for more than half (57%) of the fluctuations in seasonal surface water storage.

Human interventions

The satellite measurements were used to build a dataset of global water levels from October 2018 to July 2020, covering bodies from water from the North American Great Lakes to ponds with an area less than a tenth of a square mile.

Seasonal variability in human-managed reservoirs averaged 0.86 metre, compared with 0.22 metre in natural water bodies.

"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," Stanford geophysicist Sarah Cooley from Stanford University told Brown University, where she launched the project while a graduate student there.

"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."

Why it matters

The researchers explained their work will provide a baseline for future research on how humans impact the water cycle and what that means for ecosystems around the world.

“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,” Laurence Smith, a professor of environmental sciences at Brown, said.

“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.”

You can read more about the research and how they did it here.

World Water Day

World Water Day is held on 22 March every year to raise awareness of the importance of freshwater and the challenges billions face in getting access to safe water.

A growing population, the increasing demands of human use for agriculture and industry, plus the effects of climate change all put water under threat.

The theme of this year's World Water Day is what water means to people and its true value.

Protecting a valuable resource

Efforts at raising awareness need to be coupled with action.

The World Economic Forum's Global Water Initiative attempts to 'embed water at the centre of economic growth planning'.

From the role of technology - such as the innovative use of satellite data in this research - to changing how we value water, the initative brings together public and private organizations to tackle the challenges we're faced with.

The threat is significant as well, with natural resource crisis 5th in the list of top global risks by impact in the latest World Economic Forum Risks Report.