Plants will consume more water, leaving less for people

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Contrary to the belief that more trees will change the life better the people due to climate change, a new study suggests that plants will consume more water than now.

The plants in the future would thus less water for people living in some parts of the world, says Dartmouth-led study in Nature Geoscience. The research suggests a drier future despite anticipated precipitation increases for places like the United States and Europe, populous regions already facing water stresses.

The study challenges an expectation in climate science that plants will make the world wetter in the future. Scientists have long thought that as carbon dioxide concentrations increase in the atmosphere, plants will reduce their water consumption, leaving more freshwater available in our soils and streams. This is because as more carbon dioxide accumulates in our atmosphere plants can photosynthesize the same amount while partly closing the pores (stomata) on their leaves.

The new study says that this good impact will be limitted to tropics and the extremely high latitudes, where freshwater availability is already high and competing demands on it are low. For much of the mid-latitudes, the study finds, projected plant responses to climate change will not make the land wetter but drier, which has massive implications for millions of people.

“Approximately 60 percent of the global water flux from the land to the atmosphere goes through plants, called transpiration. Plants are like the atmosphere’s straw, dominating how water flows from the land to the atmosphere. So vegetation is a massive determinant of what water is left on land for people,” explained lead author Justin S. Mankin, an assistant professor of geography at Dartmouth and adjunct research scientist at Lamont-Doherty Earth Observatory at Columbia University.

“The question we’re asking here is, how do the combined effects of carbon dioxide and warming change the size of that straw?”

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