Impact of Ground Water Extraction on Earth’s Spin | 20 Jun 2023

Why in News?

A recent study published in Geophysical Research Letters has shed light on the significant impact of Groundwater Extraction on Earth's Rotational Axis and its contribution to global sea-level rise.

  • Researchers analyzed changes in the drift of Earth’s rotational pole and water movement — first, by accounting for just ice sheets and Glaciers and then by adding different groundwater redistribution scenarios.

What are the Factors Affecting Earth's Rotation?

  • Factors contributing to polar motion include Weather, Seasonal Changes, the molten Core, and powerful Hurricanes.
    • Polar motion is the movement of the Earth's rotational axis relative to its crust, reflecting the influence of the material exchange and mass redistribution of each layer of the Earth on the Earth's rotation axis.
    • Generally, polar motion is caused by changes in the hydrosphere, atmosphere, oceans, or solid Earth.
  • Earth’s Geographic North and South Poles are where its axis intersects the surface; however, they are not fixed. The axis and hence the poles fluctuate due to variations in the Earth’s mass distribution.
  • In the past, the poles’ drift was only caused by natural forces like ocean currents and the convection of heated rock deep beneath the Earth.
  • But the new research pitched the redistribution of groundwater as the primary culprit for the drift.
    • Water’s role in altering the Earth’s rotation was discovered in 2016, and until now, the contribution of groundwater to drifts has been unexplored.

What are the Key Findings of the Study?

  • Earth’s Tilt:
    • Groundwater pumping has tilted Earth nearly 80 centimeters east between 1993 and 2010 alone.
    • The water circulated across the planet determines how mass is distributed.
      • Between 1993 and 2010, people pumped 2,150 gigatons of groundwater, or more than 6 millimeters of sea level increase.
  • Impact on Polar Drift:
    • Excessive groundwater pumping has caused the Earth's pole to drift at a rate of 4.36 centimeters per year between 1993 and 2010, making it the climate-related factor with the greatest impact on polar motion.
    • Redistributing water from the mid-latitudes significantly influences polar drift; therefore, the location of redistribution determines polar drift.
      • During the study period, most redistribution occurred in western North America and northwestern India — both located at mid-latitudes.
  • Impact of Groundwater Pumping on Sea-Level Rise:
    • Groundwater pumping contributed to a sea-level rise of 6.24 mm during the mentioned period.
    • Pumping from mid latitude areas, such as northwest India and western North America, has the most substantial influence on Earth's axis drift.
  • Impact of Polar Drift:
    • The rotational pole normally changes by several metres 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.
  • Recommendations:
    • Attempts to slow groundwater depletion rates, especially in those sensitive regions, can theoretically alter the change in drift, but only if such conservation approaches are sustained for decades.

What is the Significance of the Study?

  • The findings emphasize the need to address groundwater depletion and its consequences on a global scale.
  • This finding underscores the importance of considering groundwater depletion as a crucial factor in analyzing Earth's rotational dynamics and rising sea levels.

Source: DTE