Is Groundwater Depletion Causing Sea-level Rise?

by Lakis Polycarpou | November 10, 2010

A recent study from Yoshihide Wada and other researchers from Utrecht University attempted to assess the status of global groundwater depletion—that is, the amount of water that is being drawn out from underground reservoirs that is not being replaced by precipitation—and came up with some startling conclusions. Chief among them that depletion of groundwater may be contributing to as much as 25 percent of observed sea-level rise in recent years.

What does this mean? Try to imagine it this way: human beings have stuck giant straws into the ground all over the world and are sucking out ancient water that has been there for, in some cases, millennia. That water is initially used to irrigate crops, water lawns, etc, but then it has to go somewhere, eventually into the sea. Or to put it another way, as Duke University’s Bill Chameides puts it, “Mankind is moving buckets and buckets of water from land to the ocean.”

To conduct their study the authors extracted country-based data on groundwater use, combined it with estimates of water demand (based on population density and location of irrigated areas) to determine how much groundwater was being withdrawn. They then subtracted that figure from an estimated rate of groundwater recharge.

Patrick J. Michaels, a climate change “skeptic” who writes for the Cato Institute has already seized on the study as supposed evidence that global warming isn’t as bad as we think. Under a part of his blog “The Current Wisdom” subtitled, “More Good News About Sea Level Rise” he writes that the Wada study “estimates that about 25% of the current sea level rise has nothing whatsoever to do with “global warming” from any cause, but instead is contributed by our increasing removal of fossil groundwater to suit our growing water demands.”

But as Chameides points out “the groundwater depletion story of Wada et al doesn’t change the big-picture story of climate change and sea-level rise. Should the Greenland or Antarctic ice sheets go, the contribution to sea level from groundwater depletion will be … well, like a drop in the bucket.”

In fact, according to Chameides, the IPCC suggested that groundwater might be contributing to sea-level rise, but did not quantify how much because of uncertainties. Furthermore, as far as I know no one has studied to the degree to which the human pressure to accelerate groundwater depletion is exacerbated by increasing drought caused by climate change.

One thing is for sure though – for anyone who has studied the issue, there is no “good news” in the depletion of groundwater at such staggering scales. Take India, where the exploitation of groundwater is already taking a massive toll—in the form of lost productivity, huge government costs for subsidies and energy consumption, unstable electrical infrastructure, unsustainable debt burdens, displaced and suicidal farmers, families suffering from fluoride poisoning (a result of ever-deeper drilling of wells) and saltwater intrusion among many other consequences.

As Marc Bierkins, one of the Utrecht University study authors, told Physorg.com,

If you let the population grow by extending the irrigated areas using groundwater that is not being recharged, then you will run into a wall at a certain point in time, and you will have hunger and social unrest to go with it . . . that is something that you can see coming for miles.”

Consequences are not limited to the developing world, though—two of the areas most at risk of groundwater depletion according to the study are the Midwest United States (which sits above Ogallala, a massive fossil aquifer) and California—two ends of the breadbasket of the U.S. and much of the world.

In the end, many of the solutions to groundwater depletion end up sounding a lot like those put forth to mitigate climate change. Conserve both energy and water; adopt more sustainable agricultural practices; grow more trees. The real good news is that we can apply strategies to address both groundwater and climate change simultaneously — if we can find the will to do so.