London: Dams and irrigation significantly increase evapotranspiration, an effect that increases the loss of freshwater to the atmosphere, thereby reducing the water available for humans, societies and ecosystems on land, a new study has found.
The study shows that dams and irrigation considerably raise the global human consumption of freshwater by increasing evapotranspiration - evaporation and plant transpiration from the Earth's land and ocean surface to the atmosphere.
"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," said Fernando Jaramillo, postdoc at Stockholm University in Sweden.
The researchers have compiled and analysed 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 per cent. The increase in total freshwater loss from the landscape to the atmosphere from human activities is calculated to be around 4,370 cubic kilometres per year, researchers said.
This corresponds to two thirds of the annual flow of the Amazon River, the world's largest river by discharge, they said.
"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," said 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," Destouni said.