Groundwater extraction linked to drift in Earth's rotational pole

The capacity of water's mass to influence the Earth's rotation was found only in 2016. 

Scientists previously calculated that humans pumped approximately 2,150 gigatonnes of groundwater from 1993 to 2010 at the worldwide level.

However, until this new study, it was unclear how groundwater contributed to the nudge in the rotational pole of the Earth. 

The authors developed a computational model to assess changes in the drift of the Earth's rotational pole. The researchers initially included scenarios of ice sheets and glaciers, and then scenarios of groundwater redistribution.

And it turns out that the model only matched the previously reported polar drift when 2,150 gigatonnes of groundwater redistribution were added to it. 

“I’m very glad to find the unexplained cause of the rotation pole drift,” Seo said. “On the other hand, as a resident of Earth and a father, I’m concerned and surprised to see that pumping groundwater is another source of sea-level rise.”

2,150 gigatonnes of groundwater extraction equate to an increase in sea level of more than 6 millimeters (0.24 inch) in this mentioned time frame. But how does groundwater extraction contribute to sea-level rise? This is due to the fact that the majority of groundwater pumped eventually ends up in the sea. 

Regions with high water redistribution 

The study discovered that a large amount of groundwater redistribution occurred in western North America and northern India between 1993 and 2010. 

The authors suggest that the nation's efforts to decrease groundwater depletion, particularly in those high-used areas, may theoretically alter the change in drift. However, this is only achievable if such conservation efforts are properly adhered to over decades. 

But does this change in the rotational pole impact the seasons on the Earth? The answer is no. “The rotational pole normally changes by several meters within about a year, so changes due to groundwater pumping don’t run the risk of shifting seasons. But on geologic time scales, polar drift can have an impact on climate,” explained Surendra Adhikari, a research scientist at the Jet Propulsion Laboratory who was not involved in this study. 

The study is published in the journal Geophysical Research Letters.

Study abstract:

Climate model estimates show significant groundwater depletion during the 20th century, consistent with global mean sea level (GMSL) budget analysis. However, prior to the Argo float era, in the early 2000’s, there is little information about steric sea level contributions to GMSL, making the role of groundwater depletion in this period less certain. We show that a useful constraint is found in observed polar motion (PM). In the period 1993–2010, we find that predicted PM excitation trends estimated from various sources of surface mass loads and the estimated glacial isostatic adjustment agree very well with the observed. Among many contributors to the PM excitation trend, groundwater storage changes are estimated to be the second largest (4.36 cm/yr) toward 64.16°E. Neglecting groundwater effects, the predicted trend differs significantly from the observed. PM observations may also provide a tool for studying historical continental scale water storage variations.