Among areas at risk, they cite India, Argentina, Australia, California or southern Europe, in a study presented at the annual conference of the American Geophysical Union, being held this week in San Francisco (California).
A new computer model, the water stored in the upper basement of the Ganges basin in India and in the south of Spain and Italy could be depleted between 2040 and 2060.
It could also be the case in the Central Valley of California and in the Tulare Basin and in the southern San Joaquin Valley also located in that State of the American West where groundwater reserves could be drained by the 2030s.
And aquifers of the southern Great Plains, which supply water to a portion of Texas, Oklahoma and New Mexico, could reach their limits between 2050 and 2070, experts anticipate.
According to them, up to 1.8 billion people could be living in areas where water supplies are almost or fully exhausted due to excessive pumping from aquifers for human consumption and for agricultural crops.
"Many aquifers are already at the limit of the operation or will become in the near future, especially in the aridest regions of the Earth where we practice very intensive irrigation," warned Inge de Graaf, hydrologist at Colorado School of Mines, considering imperative to know the limits of underground water resources.
- 20% of over-exploited reserves -
Several studies based on satellite observations had shown that several major aquifers in the world were close to exhaustion.
But such observations do not measure the level of smaller reserves, regionally, say the surveyors.
Their new approach, based on computer modelling, measured the structure of the ground water, the pumping volume and the interactions between these aquifers and surrounding water bodies like rivers and lakes.
According to experts, this modelling also predicts when the level of these aquifers will be too low for modern pumps can extract water.
According to the study, the drier regions with massive irrigation are most threatened by depletion of ground water at an earlier date. The authors cite the Great Plains, the Ganges basin and parts of Argentina and Australia.
This study estimates the limits of water supplies in the basement on a regional scale but scientists still do not have complete data on the geological structure or on the aquifer storage capacity, which would assess precisely the volume of water contained in each of these natural reservoirs.
"We do not know how much water remains in these aquifers and how quickly they will be exhausted before the devastating effects occur as dewatering wells or rivers," said Inge de Graaf.
According to a UN report in 2014, global demand for water wings and 20% of underground reserves are already overexploited. The authors call for radically changing the use and management of this resource to avoid a serious shortage by 2030, stressing that "there is enough water to meet the growing needs of the world, but not without radically changing the how water is used, managed and shared. "
In addition, climate change will alter rainfall, often at the expense of the already arid especially as the Mediterranean or sub-Saharan Africa.