Here is a connection that may not be so obvious – accelerating ground water depletion worldwide is adding to sea level rise. That is the finding of a forthcoming study – A Worldwide View of Groundwater Depletion by Dr. Marc Bierkens of Utrecht University – slated for publication in Geophysical Research Letters, a journal of the American Geophysical Union.
How might that be possible? Well, the water has to go somewhere. Once its pumped out of the ground and used for its intended purpose, much of it ends up in the oceans, either through evaporation and precipitation or direct flow into the seas. Yes, some of it does infiltrate back into the soil and recharges underlying aquifers. Yet, according to the study, as much as 25% of annual sea level rise can be attributed to ground water withdrawn by human ingenuity.
Dr. Ramón Llamas, Emeritus Professor of Hydrogeology at the Complutense University of Madrid, Spain, has termed the growing global exploitation of ground water resources a silent revolution for its stealthy expansion and the lack of attention in both national and international water law and policy. It is high time that governments and policy-makers begin focusing on both domestic and transboundary aquifers and their sustainable management, not only to protect these dwindling and threatened sources of fresh water, but also to consider the global impact that their utilization is having on communities, dependent ecosystems, and now sea level.
You can read more about this forthcoming study in the press release AGU just issued. Here is an excerpt:
In recent decades, the rate at which humans worldwide are pumping dry the vast underground stores of water that billions depend on has more than doubled, say scientists who have conducted an unusual, global assessment of groundwater use.
These fast-shrinking subterranean reservoirs are essential to daily life and agriculture in many regions, while also sustaining streams, wetlands, and ecosystems and resisting land subsidence and salt water intrusion into fresh water supplies. Today, people are drawing so much water from below that they are adding enough of it to the oceans (mainly by evaporation, then precipitation) to account for about 25 percent of the annual sea level rise across the planet, the researchers find.
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Applying these techniques worldwide to regions ranging from arid areas to those with the wetness of grasslands, the team finds that the rate at which global groundwater stocks are shrinking has more than doubled between 1960 and 2000, increasing the amount lost from 126 to 283 cubic kilometers (30 to 68 cubic miles) of water per year. Because the total amount of groundwater in the world is unknown, it’s hard to say how fast the global supply would vanish at this rate. But, if water was siphoned as rapidly from the Great Lakes, they would go bone-dry in around 80 years.
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The new assessment shows the highest rates of depletion in some of the world’s major agricultural centers, including northwest India, northeastern China, northeast Pakistan, California’s central valley, and the midwestern United States.
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Most water extracted from underground stocks ends up in the ocean, the researchers note. The team estimates the contribution of groundwater depletion to sea level rise to be 0.8 millimeters per year, which is about a quarter of the current total rate of sea level rise of 3.1 millimeters per year. That’s about as much sea-level rise as caused by the melting of glaciers and icecaps outside of Greenland and Antarctica, and it exceeds or falls into the high end of previous estimates of groundwater depletion’s contribution to sea level rise, the researchers add.