Kenneth Glad
Large-scale groundwater pumping is draining underground reserves and moving enough mass to affect Earth’s rotation. The finding highlights an unusual connection between everyday water use and planetary-scale measurements.
Groundwater depletion has been linked not only to shrinking underground reserves, but also to measurable changes in the oceans and in Earth’s motion.
The underlying study, published in the peer-reviewed journal Geophysical Research Letters, examined the years 1993 to 2010. It estimated that humans pumped about 2,150 gigatons of groundwater during that period.
That water was used mainly for drinking supplies, agriculture and industry. But after groundwater is brought to the surface, it does not remain locked in one place.
Some of it eventually moves through rivers, streams and other systems before reaching the ocean.
The study connected that transfer of water to more than 6 millimeters, or about 0.6 centimeters, of global sea-level rise. WP Tech compared the figure with average global sea-level rise of about 3.3 millimeters per year.
Rotation, not tilt
The same movement of water also affected Earth’s balance. According to the study groundwater redistribution helped shift the planet’s rotational pole nearly 80 centimeters east between 1993 and 2010.
That does not mean Earth’s seasonal tilt has suddenly changed, or that people should expect altered seasons because of the finding.
The research deals with polar motion, which describes how Earth’s rotational pole moves relative to the planet’s crust.
The change is small in ordinary terms, but it is large enough to be detected through scientific measurements.
The model lined up with observed polar drift only when groundwater redistribution was added, according to the study.
This makes groundwater depletion more than a local resource issue. Water pumped for farms, cities and factories can eventually become part of a global shift in mass, with effects that scientists can measure in both ocean levels and Earth’s rotation.
Regions that matter
Location was important in the result. The American Geophysical Union reported that groundwater loss from midlatitude regions has a stronger influence on polar motion than water removed from some other areas.
The study identified western North America and northwestern India as especially important regions during the period examined.
Those areas fall within the broader midlatitude zones where the redistribution of mass had a greater effect on Earth’s rotational pole.
Ki-Weon Seo, a geophysicist at Seoul National University and lead author of the study, said:
“Our study shows that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole.”
The finding does not suggest an immediate threat from the pole shift itself. The more practical concern is what groundwater loss means for water security and coastal risk.
As pumped water eventually adds to the oceans, it becomes one more factor contributing to pressure on shorelines already facing higher seas, erosion and flooding.
Sources: WP Tech, Geophysical Research Letters, American Geophysical Union.
