Millions of wells are at risk of running dry as overuse and arid conditions empty aquifers from California to Iran
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| Groundwater levels are falling across the globe (Credit: Sierralara/Shutterstock) |
Groundwater levels in many parts of the world are declining at concerning rates, according to the most detailed view of the problem yet. This threatens an essential supply of water for people, agriculture and ecosystems.
For years, satellites have recorded rapid declines in groundwater, from California’s Central Valley to northern India. But such gravity-based measurements can’t capture changes at a more local scale.
To get a clearer picture of the problem, Scott Jasechko at the University of California, Santa Barbara, and his colleagues analysed groundwater levels in more than 170,000 wells. The researchers focused on wells for which they had at least eight years of data since 2000. These sites represented nearly 1700 systems of aquifers, or groundwater reservoirs, around the world.
More than a third of the aquifers they studied saw water levels decline by more than 0.1 metres per year, on average, since 2000. Just over 10 per cent saw rapid declines of more than 0.5 metres per year. And a few outliers saw extreme declines of more than 1 metre per year.
Jasechko says wells are already running dry in many aquifers around the world, and millions of other shallow wells are at risk given these rates of decline.
Graham Fogg at the University of California, Davis, says groundwater declines can create serious issues long before aquifers are fully depleted. They can allow salt to contaminate the water supply, cause the land to sink and even dry out wetlands.
The researchers also found the rate of decline since 2000 had increased in about a third of the aquifers for which data was available compared with the rate over the previous two decades. “The problem is getting worse faster,” says Jasechko.
Patterns in the data point to two major culprits: rainfall and intense farming. Most of the aquifers with faster rates of decline saw below-average precipitation since 2000, and they are in arid places with irrigated agriculture. In these places, water is often pumped out of aquifers faster than it can flow back in. Such over-exploitation of groundwater is a “broad, even global scale problem”, says Fogg, adding that this study brings the issue into “sharper focus”.
But groundwater loss isn’t inevitable, says Jasechko. In about half of the aquifers for which there was data, declines have slowed or even reversed this century. That suggests efforts to stem the depletion, such as increasing the cost of pumping water, can work.
Journal reference:
Nature
DOI: https://doi.org/10.1038/s41586-023-06879-8