January 30, 2024: Groundwater-level declines have accelerated over the past four decades in 30% of the world’s regional aquifers, according to a study in 40 nations.
Researchers at the University of California’s Santa Barbara’s Environmental Studies Program analysed groundwater-level trends, for 170,000 monitoring wells and 1,693 aquifer systems in countries that encompass approximately 75% of global groundwater withdrawals.
The groundwater levels have declined more than 0.1 meter a year by 36%, or 617, by them.
“This study was driven by curiosity. We wanted to better understand the state of global groundwater by wrangling millions of groundwater level measurements,” said lead author Debra Perrone, an associate professor in UC Santa Barbara’s Environmental Studies Program.
Cleaning, sorting data
The team compiled data from national and subnational records and the work of other agencies. The study took three years, two of which were spent just cleaning and sorting data.
That’s what it took to make sense of 300 million water level measurements from 1.5 million wells over the past 100 years.
The measurements provide new constraints on the prevalence of rapid and accelerating groundwater-level declines and their correlation with land use and climatic drivers, the authors wrote in Nature journal.
Groundwater is the primary water source for many homes, farms, industries and cities around the globe.
Unsustainable groundwater withdrawals and climate changes can cause groundwater levels to fall making groundwater resources less accessible, the authors stated.
The researchers said that early twenty-first-century precipitation rates were lower than in the late twentieth century in most aquifer systems exhibiting accelerating groundwater-level declines. This highlighted a potential link between decadal-scale climate variability and accelerating groundwater-level declines.
Declines in precipitation can cause groundwater levels to fall as a result of both indirect impacts — increased groundwater abstractions during droughts, and direct impacts — reduced recharge rates during droughts.
In 16% of the aquifer systems, groundwater level declines reversed— in which groundwater levels declined in the late twentieth century but rose in the early twenty-first century. They cited the Bangkok Basin as an example.
Across the 1,693 aquifer systems, rates of groundwater-level declines were significantly correlated with the proportion of land under cultivation.
Groundwater deepening is more common in drier climates, with accelerated decline especially prevalent in arid and semi-arid lands under cultivation — “an intuitive finding,” said co-lead author Scott Jasechko, an associate professor in the university’s Bren School of Environmental Science & Management.
“But it’s one thing for something to be intuitive. It’s quite another to show that it’s happening with real-world data. This study shows that humans can turn things around with deliberate, concentrated efforts,” Jasechko said.