Aquifers are depleting more and more quickly

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The immense Ogallala aquifer crosses eight US states, from South Dakota to Texas.

Associated Press

Groundwater that supplies farms, homes, industries and cities is depleting around the world and, in many places, faster than in the last 40 years, a new study suggests. which recommends urgently tackling this exhaustion.

The researchers, whose work was published Wednesday in the journal < em>Nature, indicated that the declines were more pronounced in dry regions where cultivated land is extensive. Positive: They found several examples of aquifers that were helped to replenish by changes in water policy or management.

Our study is a story of good news and bad news, said Scott Jasechko, professor of water resources at the University of California, Santa Barbara and author principal of the study. The novelty of the study lies in its global scope.

Groundwater is one of the largest sources of fresh water in the world, making aquifer depletion a major concern. Over-pumping of aquifers can cause soils to sink and wells to dry up, threatening water resources for residential development and farms that use it to irrigate fields.

Jasechko and his colleagues analyzed groundwater data from 170,000 wells and nearly 1,700 aquifers in more than 40 countries, covering 75% of all groundwater withdrawals. For about a third of the aquifers they mapped, they were able to analyze groundwater trends this century and compare them to levels in the 1980s and 1990s.

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This analysis helped provide a more complete picture of the players' reserves. groundwater and the way in which agricultural operations and, to a lesser extent, cities and industries, strain the resource almost everywhere. Researchers and other experts have also pointed out that governments are not doing enough to regulate groundwater in most parts of the world.

That's the key point, said Upmanu Lall, professor of environmental engineering at Columbia University and director of the Columbia Water Center , who did not participate in the study. Groundwater depletion continues unabated in most parts of the world.

In about a third of the 542 aquifers for which researchers were able to analyze several decades of data, they found that depletion was greater during the 21st century than in the last 20 years of the previous century. .

In most cases, this happens in places that have also received less precipitation over time, they found. Aquifers in arid areas where agriculture is important, in places such as northern Mexico, parts of Iran, and southern California, are particularly vulnerable to depletion rapid growth of groundwater, according to the study.

But there are reasons to hope, Mr. Jasechko said.< /p>

Indeed, in about 20 percent of the aquifers studied, the authors found that the rate at which groundwater levels are falling in the 21st century has slowed compared to the 1980s and 1990s.

Our analysis suggests that long-term groundwater losses are neither universal nor irreversible, the authors write. However, in a follow-up interview, one of them, Richard Taylor, professor of hydrogeology at University College London, said that pumping too much Groundwater can irreversibly damage aquifers when it causes land subsidence and the aquifer can no longer store water.

In Saudi Arabia, groundwater depletion slowed over the century in the Eastern Saq aquifer, researchers found, perhaps because of changes the desert kingdom made to its agricultural practices in recent decades, such as banning certain water-intensive crops, to reduce water use.

Another example highlighted by the study is Thailand's Bangkok Basin, where groundwater levels increased in the early 21st century compared to previous decades. The study authors cited groundwater pumping fees and licenses established by the Thai government as possible reasons for the improvement.

Outside Tucson, Arizona, they cited a groundwater recharge project, in which surface water from the Colorado River is stored underground, as another example of a groundwater recharge project, in which surface water from the Colorado River is stored underground. significant increase in groundwater levels during the 21st century.

This means that it is possible to act, but also that there are lessons to be learned, said Mr. Taylor.

Hydrologists, policymakers, and other water experts often describe groundwater as a local or hyperlocal resource, because of the dramatic differences in how water moves through rocks and soils in different aquifers.

We cannot extrapolate from one region to another, but we can clearly see that depletion is faster than growth, recalled Felicia Marcus, former California water official and member of the Water in the West program at Stanford University, who did not participate in the study.

According to Ms. Marcus, this means that intervention is necessary.