Enlarge / Satellite measured elevation loss (greatest in the dark blue) between 2011 and 2017.

The linear break in color is an inactive fault that walls off part of the aquifer. (credit: ASI/University at Buffalo/NASA-JPL/Caltech/Google Earth/U of Basilicata)
The GRACE satellites are, unfortunately, about to die.

The pair of formation-flying gravity sensors has provided revolutionary data over the past 15 years, tracking ice loss and groundwater depletion through the subtle change in gravity triggered by that lost mass. Replacements will hopefully be launched soon.
But GRACE isn’t the only way to track groundwater in places like California. InSAR is a satellite radar measurement technology that can detect extremely small changes in ground elevation—including before-and-after mapping of the shifts around an earthquake.

But they also work well for tracking elevation changes that occur as areas gain or lose groundwater.

A new study takes advantage of that to track the golden state’s response to its recent drought, and it even detected changes due to the policy response.
Rise and fall
Parts of California have lost impressive amounts of elevation over the years as groundwater levels were lowered.

The loss of water in between grains of sediment allows the sediment to compact more densely.

And if you compact the sediments, the surface elevation drops.
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