Satellites track Indian water loss

Water is being used faster than nature can replenish supplies in Northern India, with new satellite data suggesting the rate of depletion is faster than previously feared.

The Indian government has long known that the states of Rajasthan, Punjab and Haryana have all of the ingredients for groundwater depletion: staggering population growth, rapid economic development and water-hungry farms, which account for about 95% of groundwater use in the region.

But data from a NASA satellite that can 'see' water stored deep underground has suggested that the problem is more pressing than suspected, with water levels dropping by a metre every three years.

The two Gravity Recovery and Climate Experiment (GRACE) satellites orbit the earth around 130 miles apart and the slight changes that they track in gravitational pull can be analysed to assess the amount of groundwater beneath the surface.

Put simplistically, they act like fishing floats on the surface of a lake, and when one bobs, the other takes note and records the strength of the pull from below.

The satellites can be used to pinpoint potential water shortages around the world and assess their urgency.

"Using GRACE satellite observations, we can observe and monitor water changes in critical areas of the world, from one month to the next, without leaving our desks," said NASA scientist Isabella Velicogna.

"These satellites provide a window to underground water storage changes."

Hydrologist Matt Rodell, who is based at NASA's Goddard Space Flight Center in Maryland, said: "If measures are not taken to ensure sustainable groundwater usage, consequences for the 114 million residents of the region may include a collapse of agricultural output and severe shortages of potable water."

Sam Bond




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