New research into how regions use and replenish groundwater shows that parts of the United States, southern Europe and India may see wells run dry in the next few decades.
"Already we see that many aquifers around the world are depleted," Colorado School of Mines hydrologist Inge de Graaf told reporters at the American Geophysical Union conference in San Franciso.
De Graff, who will be presenting her research on Thursday, said she was interested in learning where and when particular regions reach the limits of available groundwater for drinking, agriculture and industrial activities.
"Groundwater is the largest available freshwater resource around the world. When freshwater is not freely available, groundwater is often extracted," de Graaf said, adding that climate change likely will add to declining groundwater levels in the future.
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Areas dependent on groundwater for irrigation are most affected, the research shows.
Overall, about 8 to 9 percent of Earth's land is irrigated with groundwater, accounting for 20 percent of the world's food production, said Marc Bierkins, senior scientists at Urecht University in The Netherlands.
"If you would stop (using) the groundwater that is not renewable... about 5 or 6 percent of the food production is affected," he said.
The study shows that aquifers, which are soils or porous rocks that hold groundwater, in the Upper Ganges Basin area of India, southern Spain and Italy could be depleted between 2040 and 2060.
Aquifers in California's Central Valley, Tulare Basin and southern San Joaquin Valley could run dry even sooner, while those that supply groundwater to parts of Texas, Oklahoma and New Mexico could be depleted in the 2050s to 2070s, the study shows.
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De Graaf estimates that in less than 35 years, up to 1.8 billion people may be living in areas with groundwater levels too low to supply water for drinking and agriculture.
The study is the first to combine satellite data with regional data about aquifer structure, water withdrawals and interactions between groundwater and surrounding water. The model simulates groundwater depletion and recovery on a regional scale.
De Graff considered depletion to be reached when groundwater levels dropped more than 100 meters for two years in a row.
Scientists don't know how much water is in Earth's aquifers, but the new study at least provides an estimate of what will be available in the future, de Graff said.
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