JAIPUR: Groundwater depletion in India is a calamity that now calls for urgent measures. What is less well known, though, is that Earth's spin around its axis too is especially sensitive to changes in the mass of water beneath Earth's surface. By the law of rotation, the 45 degrees North and South latitudes would play an especially important role in determining the spin. And India's groundwater depletion has indeed been causing a shift in the axis, scientists have explained in a paper published earlier this month in the journal Science Advances.
The paper, published April 8, by Nasa scientists Surendra Adhikari and Erik Ivins of Nasa's Jet Propulsion Laboratory (JPL), Pasadena, California, built on earlier studies showing that there were connections between the Earth's movement and changes in the surface or interior of the planet.
The Earth, Nasa website explains, is still adjusting to loss of ice in North America after the last Ice Age. The reduced mass beneath North America is pulling the spin axis of Earth towards Canada, at a rate of a few inches each year.
Around the year 2000, scientists found, Earth's spin around the axis took an abrupt turn east. It is now drifting in that direction at a pace of about seven inches a year. Adhikari says the eastward shift of the axis was earlier considered to be because of the loss of mass in Greenland and Antarctica, with the rapid melting of ice. Using the monthly record of changes in mass made available through the observations of the twin satellites that are part of the Gravity Recovery and Climate Experiment (GRACE), in which Nasa collaborates with Germany, scientists found that the massive energy needed for such a shift in the axis could not be produced by the loss of mass in Greenland alone.
Something east of Greenland had to be exerting an additional pull. "The bulk of the answer is a deficit of water in Eurasia: the Indian subcontinent and the Caspian Sea area," Adhikari is quoted as saying on Nasa website.
The finding came as a surprise, because the quantity of the loss due to depletion of aquifers and drought in the area is nowhere near the losses caused by changes in the ice sheets. Earth's spin axis, though, is especially sensitive to changes occurring at 45 degrees latitude, both North and South. "That's why changes in the Indian subcontinent, for example, are so important," Adhikari explains.