According to new research that examined millions of groundwater level measurements from 170,000 wells in more than 40 nations, many regions of the world are seeing a rapid depletion in the underground water reservoirs that billions of people depend on for drinking, agriculture, and other uses. According to the researchers involved, it’s the first study to piece together what’s happening to groundwater levels globally. It will also help scientists better understand the impact that humans are having on this precious subsurface resource, either directly through overuse or indirectly through changes in rainfall linked to climate change.People depend on groundwater, which is found in aquifers—permeable rock formations with pores and fissures—especially in regions of the world like northwest India and the southwest of the United States where surface water and rainfall are in short supply.

Decreases in groundwater can cause land to sink and make it more difficult for people to get freshwater for drinking or irrigating crops.

Curiosity served as the study’s motivation. In a news release on the study that was published in the journal Nature on Wednesday, co-lead author Debra Perrone, an associate professor in the University of California, Santa Barbara’s Environmental Studies Program, stated, “We wanted to better understand the state of global groundwater by wrangling millions of groundwater level measurements.” In 71% of the 1,693 aquifer systems studied, the authors discovered that groundwater levels decreased between 2000 and 2022. Of these, 617, or 36% of the systems, had a reduction in groundwater levels of more than 0.1 meter annually.

According to the data obtained, the Ascoy-Soplamo Aquifer in Spain experienced the quickest rate of loss, with a median decline of 2.95 meters per year, according to research coauthor Scott Jasechko, an associate professor at the University of California Santa Barbara’s Bren School of Environmental Science and Management.He said, “Several Iranian aquifer systems were among those with the fastest rate of decline in groundwater.”Due to a lack of monitoring, the team was unable to collect data from most of Africa, South America, or Southeast Asia; nonetheless, according to Jasechko, the study covered the nations where the majority of groundwater pumping worldwide occurs.

Declines are not always the same

The report also included a few success stories from Arizona, New Mexico, Bangkok, and other places where groundwater has started to recover following actions taken to improve water usage regulation or reroute water to refill depleted aquifers. Jasechko emailed, “Although these ‘good news’ stories are very rare, I was impressed by the clever strategies that have been put into action to address groundwater depletion in several places.”In order to determine whether the declines observed in the 21st century were accelerating, the team also obtained groundwater level data for 542 of the study’s aquifers from 1980 to 2000. They discovered that for thirty of those aquifers, losses in groundwater levels accelerated in the first two decades of the twenty-first century, surpassing the declines noted between 1980 and 2000. “In the absence of any regular trends in either time period, these occurrences of accelerated groundwater-level drops are more than twice as numerous as one would predict from random fluctuations,” the report stated.

Although there were significant gaps in the data, Donald John MacAllister, a British Geological Survey hydrologist who was not engaged in the study, stated the set was still quite “impressive.”

“To the best of my knowledge, this global compilation of groundwater data hasn’t been done before, at least not on this scale,” he remarked.

“Groundwater is an extremely valuable resource, but one of the problems is that most people don’t think about it since they can’t see it. Our task is to continuously remind legislators that we have this resource, which we must protect and utilize to increase our resilience and prepare for climate change.

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