Removing Groundwater is Affecting the Earth’s Axis

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The growing demand for water on Earth is resulting in widespread global changes. Groundwater depletion has created adverse changes to the immediate environment such as land subsidence, deterioration of water quality, and the draining of underground water aquifers.

What scientists are also discovering is that the rate and magnitude of pumping water from underground sources has planetary-scale effects, specifically tilting the Earth’s axis enough so that it is now measurable by scientists.

What is the Earth’s axis?

The Earth has a natural tilt at about 23.5 degrees and spins at about 1,000 miles per hour on its north-south axis. The axis is critical for seasonal weather change and other climate-environmental effects that enable our planet’s normal cycles.

The earth against a dark background with stars and a line through the middle showing the earth's axis with the labels 23.5 degrees, Earth's Axis, and equator.
The Earth is tilted at an angle of 23.5 degrees. Diagram: NASA, public domain.

How much groundwater has been extracted?

Recent research, however, shows that this is now changing, with once again human activity affecting this change. Scientists now report that so much groundwater is being pumped out of the ground that this affects how the Earth spins on its axis and contributes to continual change.[1] 

A groundwater well with water flowing over the top with dried leaves in the background.
A groundwater well. Photo: USGS, public domain.

Between 1993-2010, a 2010 study calculated that 2,150 gigatons of water has been extracted from inside the Earth, or the equivalent of about 6 millimeters of total ocean rise if that water was placed on the Earth’s surface oceans.  

How groundwater extraction affects polar motion

To understand the impact of groundwater depletion, the study looked at polar motion. Polar motion is the movement or shift in the Earth’s rotational axis relative to its surface, often measured as the drift of the North and South poles.

Researchers modeled polar drift with and without groundwater extraction factored in. Without accounting for the 2,150 gigatons of groundwater redistribution calculated from a 2010 study, the model incorrectly calculated polar drift by or 4.3 centimeters (1.7 inches) of drift per year as shown by the dashed blue line in figure (b) below.

Two polar view maps with annotations to show the influence of different water movements such as glacier melt and groundwater extraction on solar motion.
Groundwater extraction was found to be the second largest influence on polar motion (PM) and was responsible for 4.36 cm/yr shift in the Earth’s pole shift towards 64.16°E. The total trend contributors to PM excitation are depicted with a solid blue line when groundwater depletion is considered, and with a dashed blue line when it’s not. The red arrow represents the observed PM excitation. Figure: See et al., 2023, CC BY 4.0.

The change in Earth’s axis is affecting sea level rise

Scientists have now shown that Earth’s pole has drifted towards 64.16°E at a speed of 4.36 cm/yr from 1993–2010. This means that each year we are now drifting further away from Earth’s previous axis tilt.

This has occurred mainly by so much water being extracted that it now contributes to overall sea level rise through redistribution of that water back into the oceans. Changes in pressure and mass of water between underground reservoirs and the surface change the overall mass of water and its contribution to Earth’s tilt.

Earth’s axis can be measured using radio telescope observations of immobile objects in space. Changes in mass enable the Earth to shift its axis; as more mass is placed on the Earth then that can move the Earth’s axis.

Typically this is temporary, as mass reverts back to its previous level once mass is redistributed or evolves from one form to another. The movement of molten rock between the Earth’s crust and core does also change the overall mass structure of the Earth. 

How moving water from underground to the Earth’s surface has affected tilt

Modeling now shows that groundwater extraction also has a significant contribution to long-term mass change on the Earth. The shift in water from inside the Earth to the outside has enabled a total of 78.48 centimeters of axis shift between 1993-2010.

Top and bottom graphics show the earth as a globe and as a 2D map showing how shifts in water across the Earth have change the Earth's axis.
Researchers found in a study published in 2016 that the Earth’s axis is particularly sensitive to changes that occur at 45 degrees latitude, both north and south. Groundwater depletion and drought in the Indian subcontinent and the Caspian Sea area caused a shift eastward in the Earth’s spin axis. Diagram: NASA/JPL-Caltech.

To make the overall calculation on how groundwater contributes to Earth’s tilt and its effect on total sea level rise, atmospheric pressure, ocean bottom pressure, artificial reservoirs behind dams, polar ice, mountain glacier mass, wind, current, and groundwater data had to be determined from various databases and estimates made from models. The global hydrological model PCR-GLOBWB was used to estimate total water extraction from underground reservoirs.[2]

What is also potentially worrisome is that groundwater extraction is also significantly impacting sea level rise because of this redistribution of water. Overall, the study was constrained by the fact it only went back to 1993, whereas major water extraction from underground reservoirs began earlier in the twentieth century.

This implies historical trends and total contribution of groundwater could be studied if historical water extraction estimates can be made to incorporate their potential effect on Earth’s axis tilt by accounting for this factor in modeling that also incorporates other factors, such as molten lava change between the Earth’s crust and core.  

Where groundwater pumping is happening

The overwhelming majority of this extraction also appears to be coming from India and the American West, where now decades long drought and population and agricultural growth has contributed to large-scale pumping of underground water.

Side by side shaded relief maps showing irrigation in 1955 and 2001 in shades of blue and groundwater depletion in yellow to green to red gradients.
As irrigation demands have risen, groundwater depletion has accelerated across the Western United States. Maps: NASA after data from Y. Wada et al. Global Annual Groundwater Depletion, 1900-2100 and Y. Wada et al. Global Monthly Irrigation, 1/12 deg, 1900-2005.

A study published in 2017 found that between 2000 and 2020, groundwater increased 22%. Groundwater intensive crops such as wheat, rice, sugar crops, maize (corn), and cotton are the major drivers of this increase. This study also found that almost all of the world’s breadbaskets (i.e. the prime agriculture areas of USA, Mexico, the Middle East and North Africa, India, Pakistan and China) are in regions that overly rely on aquifers for water.

Current water restrictions on underground water resources are not as strong compared to those restrictions imposted on extracting surface water. The implication of this study is that there may need to be more restrictions or alternative practices given the contribution underground water is having on overall sea level rise and the tilting of the Earth’s axis.

Furthermore, in areas such as West Texas, underground reservoirs are rapidly diminishing, leading to the loss of this water resources and effects such as the formation of sinkholes are increasing.

In California, over 5000 wells have dried out in the past decade, giving a sense of scale and how underground water extraction is beginning to have deleterious impact on groundwater resources as well as on overall sea level rise.[3]

A map of the contiguous United States and Mexico overlaid with a yellow to red heat map gradient showing areas of groundwater depletion.
Groundwater depletion across Western United States in 2020. Source: NASA, public domain.

The tilting of the axis is also important for producing accurate navigation systems such as GPS. The new study now allows us to factor in groundwater as a new impact on Earth’s tilt so that future navigation could account for what Earth’s tilt might be. The tilt of the Earth also has important implications for climate and climate future modeling.

Rising global temperatures may also contribute to Earth’s wobble, as glaciers melt, while the construction of dams are also having an effect. Overall, there needs to now be more study on different contributing factors to demonstrate how human activities may affect the Earth’s axis and how the Earth spins.

References

[1]    For more on how the Earth has now begun to tilt due to underground water extraction, see:  Seo K, Ryu D, Eom J, et al. (2023) Drift of Earth’s Pole Confirms Groundwater Depletion as a Significant Contributor to Global Sea Level Rise 1993–2010. Geophysical Research Letters 50(12): e2023GL103509. DOI: 10.1029/2023GL103509 and https://news.agu.org/press-release/weve-pumped-so-much-groundwater-that-weve-nudged-the-earths-spin/

[2]    Estimates on groundwater extraction were made based on this study:  Wada, Y., van Beek, L. P. H., van Kempen, C. M., Reckman, J. W. T. M., Vasak, S., & Bierkens, M. F. P. (2010). Global depletion of groundwater resources. Geophysical Research Letters, 37(20), L20402. https://doi.org/10.1029/2010gl044571

[3]    An article discussing the implications of Earth’s axis change can be seen here:  https://thehill.com/policy/equilibrium-sustainability/4075087-human-society-is-shifting-the-tilt-of-the-earth/.

Further resources

Adhikari, S., & Ivins, E. R. (2016). Climate-driven polar motion: 2003–2015. Science advances2(4), e1501693. DOI: 10.1126/sciadv.1501693

Buis, A., & Rasmussen, C. (2016, April 8). NASA study solves two mysteries about wobbling earth. NASA. https://www.nasa.gov/feature/nasa-study-solves-two-mysteries-about-wobbling-earth

Dalin, C., Wada, Y., Kastner, T., & Puma, M. J. (2017). Groundwater depletion embedded in international food trade. Nature543(7647), 700-704. https://doi.org/10.1038/nature21403

Konikow, L. F. (2013). Groundwater depletion in the United States (1900-2008) (p. 63). Reston, Virginia: US Department of the Interior, US Geological Survey. https://pubs.usgs.gov/sir/2013/5079/

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