As anyone who saw last week's images from Oklahoma can attest, terrible things happen above the ground out on the Great Plains. But, far down in the earth, where the 200mph winds of a tornado can never reach, a slow-motion disaster is unfolding. The water is starting to run out – and this particular disaster is not natural but man-made.
The Plains are one of my favourite parts of America. For most of us, they are fly-over territory, observed from 35,000ft as you speed from coast to coast, identifiable only by the brilliant-green circular fields created by central-pivot irrigation. Down at ground level, though, they have an extraordinary haunting beauty, a quiet boundlessness that, more than anywhere else in the country, evokes America before it became America.
But this huge wedge of land, half a million square miles in the middle of the US, is a harsh place to live. The winters are bitter, the summers relentlessly scorching, the winds ferocious. Here, where cold air from Canada collides with steamy air from the Gulf, with barely a hillock to separate them, the storms are epic and terrifying. On occasion, as in Moore, Oklahoma, last Monday afternoon, they can be deadly.
Gradually, though, as you move west towards the Rockies, "Tornado Alley" gives way to what is technically a semi-arid climate zone, where the rainfall is less than 20 inches in a normal year, and in a bad year next to none. But thanks to the water contained in a colossal aquifer called the Ogallala, left behind in the earth millions of years ago as the glaciers receded to the north, the Great Plains have become one of the planet's bread baskets.
Indeed, they've been exploited for their resources throughout recorded time: first, the bison, brought to near extinction in the late 19th century, then corn, wheat, cattle, cotton, oil and gas. The history of the Plains is one of boom and bust, where dreams seem to come true, before being brought low by Mother Nature or the markets. So it was with the 19th-century homesteads, lured by the promise of rich, unlimited farmland, only for utopia to be blown to smithereens by a collapse of agricultural prices, followed by the Dust Bowl.
The latter, too, was part of a cycle of years-long droughts that seem to afflict the region every quarter of a century or so. Naturally, lessons have been learnt. Changed agricultural practices mean that never again will millions of tons of bone-dry topsoil be blown from the ground to form the giant "dusters" that in the 1930s darkened the skies even in Washington DC. But the weather that caused the Dust Bowl wasn't a one-off. There were extended droughts in the 1890s, in the 1950s and late 1980s, and every sign is that we're in one now. In some parts of the Plains, less rain fell in 2012 than even during the driest years of the 1930s.
The fallback has always been the Ogallala, covering more than 170,000 square miles, providing fresh water when none arrived from the sky, enabling the irrigation of farms from South Dakota to the high plains of Texas. But for decades far more has been taken from the Ogallala than nature returns, even when the rains are good. Now it is running out and, once it's gone, there will be no replacing it.
The Ogallala was discovered by accident more than a century ago when a farmer sank a trial well and hit a gusher of H2O. By the 1940s, the aquifer was being drawn upon to support a rapidly expanding agricultural industry. Then, in the late 1980s, farmers in the southern plains, southern Kansas, New Mexico, Oklahoma and Texas, noticed that the output of their wells was declining.
In the Plains' northern reaches, the aquifer is still in reasonable shape. Elsewhere, however, if water continues to be drawn off at current rates, it could be virtually dry in 25 years (roughly when the next cyclical drought is due). Even reducing extraction will only defer the inevitable. And, in northern Texas especially, the inevitable is already happening: great swathes of land can no longer be irrigated, forcing farmers to rely entirely on what little rain falls.
Water – or rather the lack of it – is, of course, not a new problem in this country. The American West has been fighting over the stuff almost from the moment it was settled. The transformation of desert oases into sprawling megalopolises made possible by air conditioning, such as Phoenix and Las Vegas, has made matters worse. Tapped by half a dozen states, the Colorado river, the largest river of the south-west, now doesn't even make it across the US border, let alone to the Gulf of California, where it once emptied, 100 miles to the south.
But the Plains don't offer the sweet and sybaritic pleasures of the Sun Belt. There, today as always, boom and bust rule – and in recent years a couple of booms have put extra pressure on the Ogallala's water. The first was in biofuels, which created a surge in demand for ethanol, derived from corn, a particularly thirsty crop to which many Plains farmers switched.
Then came an even bigger fuel-related boom, the development of hydraulic fracturing, or "fracking", to prise loose vast reserves of shale oil and gas. For the Plains, the Dakotas and Oklahoma in particular, another oil boom is in full swing, akin to that triggered in the 1970s and 1980s by the Opec oil shocks. Soon, some predict, the US could be energy self-sufficient. A heady prospect indeed. But the chemical process of fracking not only needs water, it may also pollute the dwindling underground resources, hastening the day when the water is gone. But fear not. The Plains will still have tornadoes.