Satellites to track groundwater depletion?

A new twist on old tech offers novel monitoring solutions using satellite radar altimetry, thanks to research by Ohio State University.

A new twist on old tech offers novel monitoring solutions using satellite radar altimetry, thanks to research by Ohio State University.

Researchers have pioneered a tool that can track the loss of groundwater in California’s Central Valley by measuring how much the Earth is sinking.

The Central Valley supplies about one-fifth of the nation’s groundwater demand. A large part is used to provide crop irrigation and aid agricultural production.

The same area also accounts for about 75 per cent of the region’s subsidence. The leading cause of subsidence is the removal or disturbance of groundwater.

Massive groundwater pumping aggravates water scarcity, said Xuechen Yang, graduate student in earth sciences at The Ohio State University. It is further exacerbated when combined with California’s large population, long history of drought, and tendency to be battered by nearly every form of climate change.

But it is not just California that has a growing issue with water scarcity.

“By 2025, more than 5 billion people worldwide will live in water-stressed conditions,” said Yang. “Because land subsidence often makes human-made areas uninhabitable, those conditions can cause water and food insecurity issues.” These problems can lead to national security concerns, political instability, and even human migration disasters.

To help investigate solutions to these issues, Yang said that researchers are using satellite radar altimetry with creative new techniques. They hope to understand how Earth’s complex geophysical processes impact human life.

Satellite altimetry measures the time it takes a radar pulse to travel from the satellite to the Earth’s surface and back. Tiny changes in these measurements can indicate whether a specific point of land is rising or falling.

Satellite radar altimetry could be a fantastic development for groundwater depletion

“Satellite radar altimetry is a mature technology designed to measure ocean topography and monitor their changes over time,” said Yang. “Recent research demonstrated its feasibility in measuring relatively flat terrain elevation changes. That includes land subsidence over aquifers, such as Central Valley, California, and other coastal regions.”

Using altimetry data from the European Space Agency’s Cryosat-2 mission, Yang’s team generated a low-gradient, two-dimensional map of land subsidence over Central Valley.

Data from radar altimetry satellite missions were processed to create a subsidence time series. They used satellite missions such as the European Space Agency’s Envisat satellite and NASA’s and the French Space Agency (CNES)’s Jason-2 and Jason-3 satellites. After validating the Cryosat-2-derived results, the researchers were able to successfully detect the largest subsidence bowl near the city of Corcoran, California. Corcoran sinks at about a rate of about 30 to 35 centimetres per year.

Yang said more data and better processing methods are needed before their tool can detect smaller deformations in other parts of the state.

The research was presented last month at the annual meeting of the American Geophysical Union.

The study concluded that satellite altimetry could become an effective tool for monitoring land subsidence. Because of its pinpoint accuracy and long data record, Yang said the research could complement other geodetic techniques used to measure changes on the land.

“There is a very long history of drought in California. The people who live there are struggling with it continuously,” said Yang. “Our work could be used to improve groundwater aquifer monitoring systems and change hydrological policy for the better.”

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