One-third of global groundwater basins are overstressed, says study

After four consecutive years of drought and with the possibility of a mega-drought looming, California’s water problems have been in the news quite a bit recently. However, according to two new studies led by researchers at the University of California – Irvine, California may soon not be alone.

According to the researchers, 13 of the world’s 37 largest groundwater aquifers are currently overstressed and no one really knows for sure how much water is left in each. Despite the drought California’s Central Valley aquifer was only the fourth worst off on the list.

Scientists used NASA’s GRACE satellites to examine “dips and bumps” in Earth’s gravity, which are partially caused by the shifting weight of groundwater. These measurements were used to analyze 37 aquifers between 2003 and 2013.

Eight aquifers were classified as “overstressed” in that they were being heavily used with almost no replenishment occurring to offset that use. An additional five were classified as “extremely” or “highly stressed”. These were seeing heavy use but were being partially replenished through rainfall or some other source.

The three aquifers that were worse off than California’s were all found to be in areas of political and economic instability. The worst off was the Arabian Aquifer System, second was the Indus Basin of Northwestern India and Pakistan and third was the Murzuk-Djado Basin in northern Africa.

“What happens when a highly stressed aquifer is located in a region with socioeconomic or political tensions that can’t supplement declining water supplies fast enough? We’re trying to raise red flags now to pinpoint where active management today could protect future lives and livelihoods,” said Alexandra Richey in a statement.

Richey is lead author on both studies, and conducted the research as a University of California – Irvine, doctoral student.

The second study, published alongside the first in the journal Water Resources Research concludes that the amount of remaining water in the reservoirs remains largely unknown. This is the first study to analyze the problem using satellite data and the last attempt at estimates was made decades ago, using cruder methods than those available today.

“We don’t actually know how much is stored in each of these aquifers. Estimates of remaining storage might vary from decades to millennia. In a water-scarce society, we can no longer tolerate this level of uncertainty, especially since groundwater is disappearing so rapidly,” said Richey.

Jay Famiglietti, University of California – Irvine professor and senior water scientist at NASA’s Jet Propulsion Laboratory agrees.

“Available physical and chemical measurements are simply insufficient,” “Given how quickly we are consuming the world’s groundwater reserves, we need a coordinated global effort to determine how much is left,” said Famiglietti. “As we’re seeing in California right now, we rely much more heavily on groundwater during drought. When examining the sustainability of a region’s water resources, we absolutely must account for that dependence.”

Accurately answering the question of how much water remains would be no small task. It would require drilling into bedrock to determine where the moisture end. The researchers state, however, that despite the difficulty and expense, the work needs to be done before the world can get a good grasp on the state of our remaining water reserves.

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