Groundwater provides drinking water for half the world, including constituting the sole source of drinking water for 2.5 billion people. It also provides nearly half of the water used for agricultural irrigation globally. But a new study, published in the journal Science on Thursday, shows that up to 20% of it is in jeopardy.
Due primarily to overuse and drought, reserves of this crucial water source stored in crevices in rock, sand, and soil around the world are shrinking. The resulting strain on water for drinking, farming, bathing, and industrial purposes among other activities can be seen all over the world, from India to California.
“Because groundwater is a perennial resource that provides reliable water during droughts, overpumping and reductions in recharge are often both at play; that is, both impact groundwater levels simultaneously,” Scott Jasechko, assistant professor of water resources at the University of California, Santa Barbara who led the study, wrote in an email.
To quantify how dire the situation is, the report’s authors evaluated data from nearly 39 million groundwater wells in 40 countries around the globe, compiling local data on wells’ locations, depths, intended uses, and construction dates. It was an ambitious project. Just collecting all this information took them more than five years because it was often not readily available.
“Our maps are based on availability of data,” Debra Perrone, an assistant professor of environmental studies at the University of California, Santa Barbara who co-authored the study, wrote in an email. “In some places, the construction of groundwater wells is not tracked, so data are not available; in other places, the wells may be tracked, but the data may not be readily accessible to the public.”
By compiling these records, the authors found that up to 20% of the world’s groundwater wells are no more than 16.4 feet (5 meters) deeper than their local water table. That suggests that millions of wells could dry up if groundwater levels decline by just a few feet due to lowered precipitation levels, increased extraction, or both.
To make matters worse, the authors also found that newly dug wells aren’t that much less vulnerable than older ones pumped over a much longer period. That suggests that just constructing new wells isn’t a real solution to depletion.
The researchers say that simply digging deeper into the ground won’t fix the problem, either. Tapping into these deep aquifers comes with much higher costs, and even if communities can secure funding, water quality from deeper groundwater tends to be considerably worse because the water tends to be older and more affected by the minerals in the surrounding soil.
This issue will only become more urgent in the coming decades. The climate crisis is ushering in more drought and dry weather in many parts of the world, meaning aquifers will lose a key source of replenishment even as dry conditions above ground spike demand. In fact, in some places, the crisis is already upon us. An estimated 1.8 billion already live in water-stressed areas around the world, in part due to disappearing groundwater.
“There are numerous places where wells are already running dry, such as parts of California’s southern Central Valley,” said Scott. “For some, the problem of wells running dry is here and now.”
In a related perspective piece published concurrently in Science, scientists the University of Arizona and University of Saskatoon explain that without urgent action to conserve water, it will become a scarcer commodity that only the “relatively wealthy” can obtain. That could also exacerbate the risk of violent tension breaking out. Research supports this: In a 2020 study, researchers analysed conflicts in 50 poor, drought-vulnerable countries with high amounts of ongoing ethnic conflict and found that in the past 25 years, almost one in three wars broke out within a week of climate disruptions like heat waves or droughts.
“Avoiding such a scenario is clearly paramount to human security,” the perspective says.
The good news is that there are policies that could help take on this groundwater crisis. “There are many opportunities that, together, will get us on a path to sustainable groundwater management,” said Perrone.
That includes reducing demand for water by encouraging and incentivising people to use it more efficiently, and also by adopting “water-saving technologies,” said Scott. There are many approaches to this that could be effective, ranging from installing devices to shut off irrigation systems when it is raining to incentivising farmers to grow crops that are less water-intensive. Those strategies should be paired with stringent regulations on water use for agriculture and industry, and those regulations should also prioritise equity rather than large agribusiness.
In addition, the authors call for more careful monitoring of groundwater levels. Of course, more monitoring itself won’t fix the problem alone, but it could certainly make it easier for researchers to figure out how to solve it.
“Data themselves are not the solution, but they help us understand processes — human behaviours that influence demand or physical processes that inform supply — and can provide insights in how to best manage groundwater,” said Perrone.