Study shows contribution of groundwater extraction to sea level rise

According to a study published in Geophysical Research Letters, groundwater extraction has been a significant s=contributor to global sea level rise in the period between 1993 and 2010. Global sea level rise is currently associated primarily with the melting of polar ice sheets and mountain glaciers. Scientists have in the past suggested that the depletion of groundwater for irrigation and urban consumption could also contribute to a rise in sea levels, but there was so far no evidence to confirm or reject this theory. However, a group of researchers under the leadership of Ki-Weon Seo from the Department of Earth Sciences at Seoul National University have conducted research which provides the first evidence that groundwater pumping does contribute to sea level rise.

To make their argument, the researchers analysed the relationship between changes in global water storage and changes in the polar motion of the planet. Using precise observations of changes in the orientation of the earth’s axis, it is possible to relate any ‘wobbles’ of the axis with changes in the distribution of weight on the surface of the earth, including melting ice, water stored in dams, and groundwater extraction. Melting ice and groundwater extraction can be expected to contribute to sea level rise as long as this water reaches the seas and oceans. However, a large amount of surface water is also stored in dams, which limits the flows of water to the coast.

The researchers modelled the changes in the rotational pole of the earth, including insights on how changing the amount of water on the surface of the earth could affect the tilt of the earth’s axis. They compared the observed changes to predicted changes first by only considering the effect of melting ice, and then by adding in scenarios of groundwater redistribution. They found that if only melting ice is considered, the model does not correspond all to well with observed reality. However, if the displacement of groundwater is factored in, the model fits remarkably well with observations. The earth’s pole, it was found,  has drifted toward 64.16°E at a speed of 4.36 cm/year in the period  during 1993–2010 due to groundwater depletion and resulting sea level rise.