Groundwater around the planet is rapidly depleting

Groundwater levels are falling, but the good news is that this can be reversed. Success stories with proactive management policies show that this trend can be improved.

Groundwater is an important source of fresh water for agriculture, human consumption and industry in general. However, aquifers are threatened by climate change, meaning they are no longer as available and pose a threat to economies and ecosystems if overused.

Scientists from the University of California in Santa Barbara (USA) have just published in the journal Nature The world's largest ever measurement of groundwater levels covers nearly 1,700 aquifers. While satellite maps provide information about storage trends, measuring in-situ monitoring wells and analyzing them on a global scale helps scientists and governments build a more comprehensive picture of reserve trends.

Their results show a general trend of global water resource decline, with a decline of more than 0.5 meters per year in the 21st century, corresponding to a 71% decline in aquifers. But they also provide successful examples and management solutions.

This depletion can have a number of undesirable effects on human water supplies. For example, it affects a well's ability to pump water to the surface, meaning it runs dry. Likewise, excessive pumping leads to seawater intrusion or deterioration in quality. And because groundwater and surface water resources are often interconnected, such excessive abstraction can impact the amount of water available in rivers.said Debra Perrone, assistant professor in the Environmental Studies Program at American University.

The team published in the magazine Science another study of wells built in 2021. In this case, groundwater flow was monitored. “Monitoring wells give us information about supply, while groundwater wells give us data about demand,” explains Perrone.


The impacts are greater in dry regions

The researchers collected data from national, subnational and various government registries. In total it took three years, two of which were spent cleaning and classifying the data. “This is necessary to understand 300 million water level measurements from 1.5 million wells over the last 100 years.“, You say.

They then turned these numbers into real trends by reviewing more than 1,200 publications and reconstructing the boundaries of aquifers in the areas they studied. By identifying 1,693 aquifer systems around the world, they found that 36% of aquifers are shrinking by 0.1 meters per year and 12% are shrinking rapidly by more than 0.5 meters per year.

Comparing these results with groundwater depletion data from 1980 to 2000, the team found that 30% of the aquifers studied experienced rapid decline in the 21st century, particularly in drylands.

In this climate, deepening of these waters and rapid retreat are more common, especially in arid and semi-arid agricultural areas. “An intuitive discovery“said co-author Scott Jaseczko, a professor at the same university’s Bren School of Environmental Science and Management. “But it's one thing for something to be intuitive, and quite another to show what happens with real data.“he added.

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Perrone emphasized: “Water is a critical resource for human consumption, agricultural and industrial production. Groundwater is particularly important because it is a reliable, permanent source of water that can be used during droughts, when there is less rainfall and the flow of our rivers decreases. Excessive use of these groundwater resources could hinder adequate supply to important sectors during shortages.“.

Reasons for moderate optimism about groundwater

The researchers also found that 6% of the aquifers included in the data were rising at a rate of 0.1 meters per year and 1% were rising at a rate of 0.5 meters per year. This may be due to reductions in groundwater use, implementation of consumption policies, diversion of surface water or changes in land cover and managed recharge projects. “This research shows that with targeted, focused efforts, people can make a differenceYasechko emphasized.

An example is Tucson, Arizona. Water from the Colorado River is used to recharge the aquifer in the nearby Avra ​​Valley. The project preserves this resource for future use. “Groundwater is often viewed as a bank account. By selectively recharging aquifers, we can store this water until we need itsaid Jasechko.
However, diversion of water flow has caused the Colorado River to flow less, so that it rarely reaches the Gulf of California delta.

Our work shows that we can be cautiously optimistic, as our data shows that more than 100 aquifers have slowed, stopped or reversed groundwater decline. Caution is required in the sense that the rate at which the water level is falling is much greater than the rate at which the groundwater level is rising: it is easier to make the situation worse than to improve itPerrone said.

The collected groundwater can also benefit the region's ecosystem. In fact, when Perrone prepared his research report in 2014, he found that aquifers could hold six times more water per dollar than surface reservoirs. Another option they suggest is to focus on reducing demand.

Currently, the research team is focused on studying changes in groundwater levels over time in the context of climate change. Comparing this rate of change with the actual drilling depth allows for better prediction of when access to water is at risk.

With information from:


Debra Perrone et al. “Rapid groundwater decline in many aquifers worldwide.” Nature (2024)

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