Groundwater is rapidly declining around the world, often at accelerating rates, the largest assessment of its kind involving almost 1,700 aquifers has shown.
The three-year study by researchers at UC Santa Barbara found that groundwater is dropping in more than two thirds, or 71 per cent, of the aquifers – in three times as many times places as would be expected by chance.
And this depletion is accelerating in many places. Having declined in the 1980s and 1990s, it has since sped up in the last two decades.
The study, which included 300 million water level measurements from 1.5 million wells over the past 100 years, found that groundwater deepening is more common in drier climates, with “accelerated decline” most common in arid and semi-arid lands under cultivation.
In some countries, such as Iran, groundwater declines are widespread.
Co-lead author Scott Jasechko, an associate professor in the university’s Bren School of Environmental Science and Management, told The National irrigation is likely to blame.
“Rapid and accelerating groundwater declines are widespread in many valleys across Iran, likely due in large part to intensive groundwater pumping for irrigation,” he said.
“The accelerating pace of groundwater declines in Iran raises questions about the viability of Iranian irrigated agriculture in the near future.”
Most aquifers where declines were accelerating are in places where conditions have become drier over the last 40 years, said the authors.
It is not all bad news, however.
In some regions – such as parts of Saudi Arabia – groundwater levels have stabilised, or even recovered.
“In central Saudi Arabia, groundwater levels have declined for decades as groundwater was pumped for irrigation, but there is emerging evidence that these declines may be slowing down in central Saudi Arabia following policy changes,” said Mr Jasechko.
He added: “The study shows that humans can turn things around with deliberate, concentrated efforts.”
The study found that declines of the 1980s and ’90s had reversed in 16 per cent of the aquifer systems the authors had historical data for.
However, they said those cases are only half as common as would be expected by chance.
The problem can be halted or even reversed by reducing demand, using regulations, permitting and fees for groundwater use, said the study authors.
In Bangkok, groundwater level declines of the 1980s and 1990s were reversed by regulations designed to reduce groundwater pumping, according to the authors.
Spain has seen some success with levels in several aquifers having rebounded.
Progress has also been made in Australia, where levels in some aquifers have rebounded and are even rising.
In South Africa, levels of some aquifers have rebounded but in some places groundwater depletion is accelerating.
The picture is also mixed in the US.
Groundwater has depleted in some areas but is rising again in others. The study highlights a depleted aquifer near Tucson, Arizona, which is being refilled by water diverted from the Colorado River moved hundreds of kilometres by canals.
The UAE’s aquifers were not included in the study.
But the government has been working to reverse the decline in the country’s groundwater resources. In 2019, it was revealed that levels had fallen by as much as 14 metres in Liwa Crescent, south of the capital, in 12 years.
Last year Abu Dhabi introduced a policy to protect its groundwater, which aims to decrease extraction by up to 650 million cubic metres by 2030.
Groundwater constitutes 60 per cent of the total water used in the emirate, mainly in agriculture to irrigate crops.