7th December 2015

Global human freshwater footprint has been underestimated

Dams and irrigation raise the global human freshwater footprint almost 20 percent higher than previously thought, according to new research by Stockholm University.

A new study by Stockholm University – published in the peer-reviewed journal Science – shows how dams and irrigation considerably raise the global human consumption of freshwater, by increasing evapotranspiration. This effect increases the loss of freshwater to the atmosphere, thereby reducing the water available for humans, societies and ecosystems on land.

"Small things that we do on the surface of the Earth can have large global effects. Previously, the global effects of local human activities such as dams had been underestimated. This study shows that, so far, the effects are even greater than those from atmospheric climate change," says Fernando Jaramillo, postdoc at the Department of Physical Geography at Stockholm University.

The researchers compiled and analysed over a century of data – from 1901 to 2008 – for climate, hydrology and water use in one hundred large hydrological basins spread over the world. Their results raise the previous estimate of the global human freshwater footprint by almost 20 percent. The increase in total freshwater loss from the landscape to the atmosphere is calculated to be 4,370 km3 per year. This is equivalent to two-thirds of the annual flow of the Amazon River, the world's largest river by discharge.

"The human-caused increase in this loss is like a huge river of freshwater from the landscape to the atmosphere. We have changed so much of the freshwater system without knowing it," says Gia Destouni, Professor at Stockholm University. "Our study shows that we have already passed a proposed planetary boundary for freshwater consumption. This is serious, regardless of whether we have crossed a real boundary or if the boundary has been underestimated."

As the global population continues to increase, the situation will worsen. By 2030, the world will need at least 30 percent more water than it did in 2012, according to United Nations High Level Panel on Global Sustainability estimates.

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