While Groundwater Goes Down, Level of Earth Goes Up

The ongoing drought in the western United Sates has caused so much loss of groundwater that the Earth, on average, has lifted up by about 0.16 inches over the last 18 months, according to a new study.

The situation was even worse in the snow-starved mountains of California, where the Earth rose up to 0.6 inches.

Researchers from San Diego’s Scripps Institution of Oceanography and the U.S. Geological Survey estimated the groundwater loss from the start of 2013 to be 63 trillion gallons – the equivalent of flooding four inches of water across the United States west of the Rockies.

The study, published online by the journal Science, offers a grim accounting of the drought’s toll.

“We found that it’s most severe in California, particularly in the Sierras,” said co-author Duncan Agnew, professor of geophysics at the Scripps Institution. “It’s predominantly in the Coast Ranges and the Sierras showing the most uplift, and hence, that’s where we believe is the largest water loss.”

The 63 trillion gallons lost is about how much ice is lost from the Greenland ice cap every year due to global warming.

Scientists came to this conclusion by studying data collected from hundreds of GPS sensors across the western USA, installed primarily to detect small changes in the ground caused by earthquakes.

But the GPS data can also be used to show very small changes in elevation.

Groundwater is very heavy, and its weight depresses the Earth’s upper crust. Remove the weight, and the crust springs upward – and GPS sensors can detect how much higher the land has risen as a result of loss of groundwater.

According to the study, data showed the period of land lifting up began in 2013 and continues to this day.