Deep underneath the Great Plains states is a massive pool of water that preexists humans. For decades, the High Plains Aquifer has provided irrigation for the nation's breadbasket. But, as with other aquifers around the world, we're depleting it far faster than it's being filled — just as the prospect of climate change-related drought becomes more evident.

The drop in water levels warranted a front-page story in The Times today, but it's a problem that has been more than a century in the making. Farmers in the southwestern corner of Kansas tell The Times about how they're adjusting to wells that produce one-third of the water they did twenty years ago, switching from water-intensive corn to cows, for example.

The issue has come to a head as the region continues to suffer from the worst drought since the Great Depression. Right now, over 97 percent of Kansas is in drought, as seen below; nearly every monitoring well in the state is "much below normal" or "low." The aquifer was once a backup water source in times like this. That resource is fading.

Vast stretches of Texas farmland lying over the aquifer no longer support irrigation. In west-central Kansas, up to a fifth of the irrigated farmland along a 100-mile swath of the aquifer has already gone dry. In many other places, there no longer is enough water to supply farmers’ peak needs during Kansas’ scorching summers.

A 2009 report from the US Geological Survey outlined the threat to the aquifer. In raw figures:

The area-weighted, average water-level changes in the aquifer were a decline of 14.0 feet from predevelopment to 2009, a decline of 0.1 foot from 2007–08, and a decline of 0.3 foot from 2008–09. Total water in storage in the aquifer in 2009 was about 2.9 billion acre-feet, which was a decline of about 273 million acre-feet since predevelopment.

There's still a lot of water in the aquifer, but as levels drop, it necessarily becomes harder to access. The decline isn't uniform, as shown in the map below.

The only region showing a gain is in Nebraska, at the north end of the aquifer. This is why the government insisted TransCanada re-route its proposed path for the Keystone XL pipeline. The original route took it over the sand hills that act as a sort of sponge for the aquifer.

Through 2009, the reduction by state looks like this. Dark blue indicates less withdrawal, expressed in feet; gray, more.

The fate of the High Plains Aquifer isn't unique. Across the world, people have extracted far more water than the aquifers can replenish. A 2012 report in Nature documented the steep decline of aquifers across the world. In the map below, red aquifers are declining far faster than they can be replenished. On a global scale, the High Plains isn't doing that badly — which is bad news. As the Nature report puts it, "about 1.7 billion people live in areas where groundwater resources and/or groundwater-dependent ecosystems are under threat."


Image from Nature, via Grist.

You'll notice on that map, as on the map of the states above, that it's aquifers in drier, warmer regions that are more likely to tap the underground stores. As the High Plains Aquifer raises worries about our ability to meet our existing needs, those needs are about to become much more starkly pronounced. A draft report on the effects of climate change in the United States, released last year, indicates that land in the breadbasket, land served by that aquifer, is going to get much drier by the end of the century.

As the report says:

Based mostly on hydrologic simulations, soil moisture, especially in summer, is expected to decline with higher temperatures and attendant increases in the potential for evapotranspiration in much of the country, especially in the Southwest.

The High Plains Aquifer acts as a sort of hydrological savings account. Farmers largely relied on it in times of need, though dipping into the savings was a common practice. We're now approaching a time when we'll increasingly have to live paycheck-to-paycheck — rainstorm-to-rainstorm, if you will — right as we may also be getting a paycut.