The human impact on freshwater loss owing to activities including irrigation and dam construction is 20 per cent higher than estimated, research shows.
According to a study published on Thursday by Science magazine, the increase in the total loss of freshwater into the atmosphere by evapotranspiration, is 4370 cubic kilometres per year, equivalent to two-thirds of the annual flow of the world's largest river, the Amazon.
"Small things that we do on the surface of the Earth can have large global effects," said Fernando Jaramillo, postdoctoral fellow at Stockholm University.
"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."
The thesis of the study is that irrigation and dams have increased global human consumption of freshwater by increasing evapotranspiration, which is the loss of moisture from a surface by direct evaporation together with the loss of water by transpiration from vegetation.
Human impact increases the loss of freshwater into the atmosphere and, therefore, reduces the water available to humans and related ecosystems.
"The human-caused increase in this loss is like a huge river of freshwater from the landscape to the atmosphere," said Gia Destouni, Professor at Stockholm University.
"We have changed so much of the freshwater system without knowing it.
"Our study shows 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."
For the study the scientists had analysed data on climate, hydrology and water-use in hundreds of large watersheds of the world between 1901 and 2008.
