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Groundwater is being pumped from California’s Central Valley at a much greater rate than it can be replaced, according to a new report from NASA water scientist James Famiglietti.

The report, recently published in Nature Climate Change, is not limited in scope to California – Famiglietti warns that major aquifers worldwide are at risk – but California has some of the fastest-draining aquifers in the world.

“California’s Sacramento and San Joaquin river basins have lost roughly 15 cubic kilometers of total water per year since 2011,” he writes, which is “more water than all 38 million Californians use for domestic and municipal supplies annually—over half of which is due to groundwater pumping in the Central Valley.”

The images below illustrate the decreasing levels of groundwater in the first three years of California’s ongoing drought:

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Images by J.T. Reager, NASA Jet Propulsion Laboratory, California Institute of Technology, from “The Global Groundwater Crisis,” Nature Climate Change, November 2014, by James S. Famiglietti

Famiglietti states that, at present, regions are treating their aquifers like inexhaustible resources, when in actuality they are precious and limited. If left unchecked, drainage rates will eventually result in defunct aquifers, which could trigger “civil uprising and international violent conflict in the already water-stressed regions of the world, and new conflict in others.”

The graph below shows drainage rates at some of the largest aquifers on Earth, most of which “underlie the world’s great agricultural regions and are primarily responsible for their high productivity.”

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Image: J. T. Reager, NASA Jet Propulsion Laboratory, California Institute of Technology, USA.

Northwestern India, for example, is losing its groundwater at a much greater pace than California, though an extended drought in either region would lead to severe mortal and economic turmoil. 

And the problems will begin before the aquifers are completely drained. The lower a well’s water table drops, the higher the pumping costs – and the water at those lower levels usually has a higher salt content. The salt can kill crops and destroy soil productivity. Some almond groves in California’s Central Valley are already suffering from salty irrigation water.

And yet California’s farms need all of that water. Nearly half of all U.S.-grown fruits, nuts and vegetables come from the Central Valley, and the persistent drought has cost the state an estimated $2.2 billion in direct and indirect agricultural losses.

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