Devastating Chart Shows Why El Niño Won’t Fix the Drought

California Aqueduct
The California Aqueduct in the Mojave Desert near Palmdale, CA. Steve Proehl/Corbis Enlarge

This story originally appeared on Mother Jones and is part of the Climate Desk collaboration.

In California, news of a historically powerful El Niño oceanic warming event is stoking hopes that winter rains will ease the state’s brutal drought. But for farmers in the Central Valley, one of the globe’s most productive agricultural regions, water troubles go much deeper—literally—than the current lack of precipitation.

That’s the message of an eye-popping report from researchers at the US Geological Survey. This chart tells the story:

chart-1_0
USGS a bit bigger

To understand it, note that in the arid Central Valley, farmers get water to irrigate their crops in two ways. The first is through massive, government-built projects that deliver melted snow from the Sierra Nevada mountains. The second is by digging wells into the ground and pumping water from the region’s ancient aquifers. In theory, the aquifer water serves as a buffer—it keeps farming humming when (as has happened the last three years) the winter snows don’t come. When the snows return, the theory goes, irrigation water flows anew through canals, and the aquifers are allowed to refill.

But as the chart shows, the Central Valley’s underground water reserves are in a state of decline that predates the current drought by decades. The red line shows the change in underground water storage since the early 1960s; the green bars show how much water entered the Central Valley each year through the irrigation projects. Note how both vary during “wet” and “dry” times.

As you’d expect, underground water storage drops during dry years, as farmers resort to the pump to make up for lost irrigation allotments, and it rises during wet years, when the irrigation projects up their contribution. The problem is, aquifer recharge during wet years never fully replaces all that was taken away during dry times—meaning that the the Central Valley has surrendered a total of 100 cubic kilometers, or 811 million acre-feet, of underground water since 1962. That’s an average of about 1.5 million acre-feet of water annually extracted from finite underground reserves and not replaced by the Central Valley’s farms. By comparison, all of Los Angeles uses about 600,000 acre-feet of water per year. (An acre-foot is the amount needed to cover an acre of land with a foot of water).

 

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