Groundwater responsible for nearly half of sea level rise?
No, you don't need to check the prescription on your eyeglasses (or medications)'we really are talking groundwater depletion and sea level rise again. Just a few weeks ago, we covered a recent study on the topic published by researchers from Taiwan and the Netherlands and compared it to one from last year that was done by Leonard Konikow of the United States Geological Survey. There's a good reason that we're back at it again. But first, for those who didn't take notes'what are we talking about?
In many places, the water table is dropping as groundwater is depleted. When groundwater is pumped up for use, whether for drinking water or irrigation, some portion of it fails to infiltrate back down into the ground. (In drier regions, that portion approaches nil). Instead, the water evaporates into the atmosphere or ends up in surface streams. In either case, most of it eventually makes its way to the ocean. In many places, the amount of precipitation that infiltrates into the ground is too small to make up for that loss. And as the volume of groundwater decreases, sea level must rise in turn. It's an awfully big planet we're on, though. Most of its surface is ocean, so you might not expect this to add up to much.
That's where these studies become so interesting. They estimated that, currently, the volume of groundwater being depleted is equivalent to about 13 to 20 percent of the ocean volume change. This isn't the whole story, however. The construction of dams on rivers creates large reservoirs (or lakes) behind them, increasing the storage of water on land. As long as you keep building new dams, you continually counteract some portion of sea level rise.
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