Pumping groundwater raises sea level

Sarah Simpson lays it out for us in Discover News: Groundwater mining — pumping aquifers faster than they can be replenished — can have nasty consequences. Mining the Ogallala Aquifer (also called the High Plains aquifer), for example, has infamously run the White River dry where it once gushed over Texas' Silver Falls...

Most of the groundwater sprayed on thirsty croplands across America makes its way into streams and rivers. Even though much of the water seeps into the soil first, the vast majority never makes its way back into the aquifer. Instead, it heads toward the sea, where it eventually contributes a surprising share of global sea level rise, reports Leonard Konikow, a hydrogeologist with the U.S. Geological Survey.

In a rigorous new analysis of global groundwater depletion published earlier this month, Konikow estimated that global aquifers lost 4,500 cubic kilometers between 1900 and 2008 — enough to raise global sea level by about 12.6 millimeters. That’s a little more than 6 percent of the total sea level rise that took place over that time.

The actual impact on global sea level would have been much greater had it not been for dams, which stall groundwater’s trip to the sea. In a second paper out last week, Konikow and a group of colleagues showed that between 1972 and 2008, dams retained more water in their reservoirs than people pumped out of aquifers. Specifically, groundwater depletion contributed an average of 0.3 millimeters per year to sea level rise, whereas surface water retention decreased sea level rise by 0.4 millimeters per year.

Dams and pumps may be locked in a zero sum game for now, but the balance of power is shifting. Konikow points out a startling acceleration in groundwater depletion since 1950: one quarter of the depletion from 1900 to 2008 occurred in the final eight years. Indeed, the volume of groundwater lost between 2000 and 2008 was equal to 13 percent of global sea level rise. That means groundwater loss is accelerating right at a time when dams may be unable to keep pace; the reservoirs of old dams continue to fill with sediment, and new dam construction is expected to slow....

The White River flowing across Silver Falls in 1891. Now dried up...