Groundwater depletion adding to sea level rise

The melting of the polar ice caps gets a lot of attention for global sea level rise. But another contributing factor to higher tides is groundwater depletion.

More than 6 percent of the sea level rise in the last century is from the movement of land-locked water to the oceans. That’s according to a new study by the U.S. Geological Survey and published in the most recent edition of the journal Geophysical Research Letters.

Groundwater depletion for human consumption and agricultural and industrial uses is known to have many negative outcomes, including land subsidence, a reduction in surface water as underground springs dry up, the depletion of wetlands, and threats to long term water supplies.

Pumping groundwater to the surface also adds to sea levels as the water is used and then discharged into sewer systems and storm drains, which ultimately empty into the oceans. How much this is happening has been a bit of a mystery because of insufficient data and previous estimates have been all over the map, says the study’s author Leonard Konikow.

Konikow set out to find the answer by developing the first comprehensive estimate of changes in groundwater storage using “volumetric accounting.” He found that from 1900-2000, the U.S. has depleted 800 km^3 of groundwater, enough to bump up sea levels by 2.2 mm. The study estimates that globally, 3,400 km^3 of groundwater has been removed from 1900-2000 during that time period, adding 9.3 mm total to the seas.

The big shocker is that the rate of groundwater depletion in the U.S. and globally steadily increased between 2000-2008. That’s resulted in a grand total of 12.6 mm to the oceans since 1900, an amount that accounts for greater than 6 percent of all sources of sea level rise.

Konikow says the results will help in assessing freshwater supplies and and create greater accuracy in the prediction of sea level rise.