During the drought, California has increasingly turned to groundwater to fill the deficit. Up until last year, groundwater was unregulated in CA – if anyone owned land and drilled a borehole, they could use as much of the water they found as they liked. It made sense during a time of abundance and made it easy for farmers and other landowners that operated their own wells. About 30 million Californians rely on groundwater for a portion of their drinking supply.
But now groundwater is disappearing at an alarming rate. Unlike surface reservoirs which can replenish in a matter of one or two rainy seasons, aquifers can take tens or hundreds of years to replenish. Wells are starting to run dry. Farmers that can afford to do so, are drilling expensive deeper wells to keep their farms in operation. In a process called subsidence, the ground is compressing and collapsing – in some areas by as much as several feet – as aquifers are depleted.
Gravity Recovery and Climate Experiment (GRACE) is a joint mission of NASA and the German Aerospace Center, and has been measuring Earth’s gravity field since 2002. The mission includes twin satellites, one following the other. When one flies over a gravity anomaly, it speeds up or slows down. The distance between the satellites changes when this occurs, and by constantly measuring the distance between the two satellites and using precise GPS data, scientists can construct a map of the change in gravity across the globe. Gravity is determined by mass, and by measuring the change in gravity, GRACE shows how the distribution of mass – mostly water – varies across the planet over time. A timelapse of the changes clearly show water being removed from heavily populated areas that are digging deep into aquifers to sustain growth and demand.
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