Pumping too much groundwater has changed Earth’s spin
According to a recent study published in the journal Geophysical Research Letters, humans have caused the Earth to tilt approximately 80 centimeters (31.5 inches) eastward between 1993 and 2010 by pumping and relocating large amounts of groundwater.
The study explores the impact of groundwater redistribution on the Earth’s rotational pole, which refers to the point around which the planet rotates. Changes in the distribution of water on Earth affect its mass distribution and consequently alter the rotational pole’s position. This phenomenon, known as polar motion, is analogous to adding weight to a spinning top, thus causing it to spin differently.
“Earth’s rotational pole actually changes a lot,” said study lead author Ki-Weon Seo, a geophysicist at Seoul National University. “Our study shows that among climate-related causes, the redistribution of groundwater actually has the largest impact on the drift of the rotational pole.”
How the research was conducted
In a study from 2016, scientists first discovered that water has the ability to modify the Earth’s rotation, but until now, the specific contribution of groundwater to this rotational change had not been explored. In the current study, the researchers employed models to simulate the observed changes in the Earth’s rotational pole drift and the movement of water. Initially, the models considered only ice sheets and glaciers, but various scenarios of groundwater redistribution were subsequently incorporated.
The model’s results aligned with the observed polar drift only when 2,150 gigatons of groundwater redistribution were included. Without this factor, the model deviated by 78.5 centimeters (31 inches), equivalent to an annual drift of 4.3 centimeters (1.7 inches).
“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.”
“This is a nice contribution and an important documentation for sure,” added lead author of the 2016 study Surendra Adhikari, a research scientist at the Jet Propulsion Laboratory. “They’ve quantified the role of groundwater pumping on polar motion, and it’s pretty significant.”
The location of groundwater redistribution plays a role in determining its effect on polar drift, with midlatitude water redistribution having a greater influence on the rotational pole. The study period saw the highest volume of water being redistributed in western North America and northwestern India, both situated at midlatitudes.
Polar drift can impact the climate
Seo suggests that efforts to reduce the depletion rates of groundwater, particularly in sensitive regions, could potentially alter the rate of drift. However, he emphasizes that sustained conservation approaches would be required over several decades to achieve noticeable results. While the changes caused by groundwater pumping do not pose an immediate risk of altering seasons, Adhikari points out that on geological timescales, polar drift can impact climate.
Looking ahead, the researchers propose delving into historical data to gain further insights. “Observing changes in Earth’s rotational pole is useful for understanding continent-scale water storage variations. Polar motion data are available from as early as the late 19th century. So, we can potentially use those data to understand continental water storage variations during the last 100 years. Were there any hydrological regime changes resulting from the warming climate? Polar motion could hold the answer,” Seo concluded.
Consequences of pumping too much groundwater
Pumping too much groundwater, often as a result of overuse in agricultural, industrial, and domestic activities, can lead to several significant consequences, both environmentally and socio-economically.
Land subsidence
As groundwater is pumped from underground, the support that it provides to the overlying soil is reduced, potentially causing the land to compact and sink, a process known as land subsidence. This can lead to infrastructure damage, including buckling roads and cracking pipelines, and increases the risk of flooding.
Saltwater intrusion
In coastal areas, overpumping groundwater can lead to saltwater intrusion. Freshwater is less dense than saltwater, so it typically lies above saltwater in aquifers near the coast. When excessive groundwater is withdrawn, the pressure of freshwater decreases, allowing saltwater to move inland or upward, which can contaminate drinking water supplies and render the soil less productive for agriculture.
Depletion of water table
Over-extraction can deplete the water table, causing wells to go dry and leading to a water shortage. In severe cases, it can result in water crises, affecting agricultural productivity and domestic water supply.
Ecological consequences
Groundwater feeds into rivers, lakes, and wetlands, and is vital to maintaining their flow levels. A reduction in groundwater can therefore damage these ecosystems and harm the wildlife that depends on them.
Decreased water quality
Overpumping can reduce the natural filtration that occurs as water percolates through the ground, leading to lower water quality.
Socio-economic impact
The aforementioned issues can significantly impact agricultural productivity, potentially leading to increased food prices and food insecurity. Additionally, the cost of accessing water can rise, as deeper wells need to be dug or water needs to be transported from further away.
Increased energy costs
More energy is required to pump groundwater from deeper levels, contributing to higher energy usage and associated environmental and economic costs.
Climate change impacts
Groundwater depletion contributes to sea-level rise. When water is pumped from the ground and used, it eventually makes its way to the sea, increasing its volume.
Sustainable groundwater management is crucial to prevent these adverse effects. This might include implementing regulations to control over-extraction, adopting more water-efficient farming practices, recharging aquifers where possible, and raising awareness about water conservation among the public.
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By Andrei Ionescu, Earth.com Staff Writer
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