Quotes of the Day

Quite by accident a couple of weeks ago — I was looking for a vineyard — I found myself driving through the northern reaches of California's Central Valley, the verdant and productive fruit and vegetable basket of the U.S. To the left and right of highway 101 were fields of produce stretching to the horizon, just a small section of an agricultural superpower that produced $21 billion worth of fruits and vegetables in 2007. It's the rich soil and perfect climate that has helped make the Central Valley so productive, but something else has made a big difference as well: irrigation. Fountains running up and down the fields sprinkle a steady stream of water onto the soil, without which farming on such a massive scale would be all but impossible in this dry climate. And that water comes from both the ground — farmers pumping deep water to the surface — and from a sprawling irrigation network that is fed in part by the great Colorado River.

Or at least, it used to be great. These days the Colorado River — which starts in the Rocky Mountains and cuts through much of the Southwest — isn't what it once was. The water of the river has been dammed and divvied up, with more than 40 million people in the region now depending on it for irrigation and municipal supplies. But persistent drought along with the growth in the West has reduced the river's flow, to the point that these days it usually dries up before it reaches what had been its mouth on the Pacific coast of Mexico. We're draining the river dry.

And this year is likely to be worse than most. The Southwest is still recovering from a historic drought that lasted much of the previous year, setting off wildfires and severely damaging agricultural output. Snowpack across the Colorado River Basin — important because melting snow in the spring helps feed the river — was less than half normal levels, which made for a terribly dry spring. Water levels at Lake Mead — the man-made reservoir created by the Hoover Dam near Las Vegas — was barely half full at the end of April, and is expected to drop another 14 ft. this summer. By mid-April 61% of the lower 48 states were listed by the U.S. Drought Monitor as being in abnormally dry or drought conditions. Already wildfires are sweeping across New Mexico. The West is set to burn this summer, once again.

But what's really scary is what long-term changes in water availability and water use could mean for our ability to feed ourselves. That's the subject of a new paper in the journal Proceedings of the National Academy of Sciences, in which researchers from the University of Texas and the U.S. Geological Survey looked at the level of groundwater depletion in the Central Valley and in the High Plains of the Midwest, home to the country's breadbasket. They found that during a recent intense drought between 2007 and 2009, farmers in the southern half of California's Central Valley depleted enough groundwater to fill all of Lake Mead — a rate of depletion that is utterly unsustainable.

In the High Plains, groundwater levels have steadily declined since the 1950s, falling by 150 ft. in some areas. In parts of the southern High Plains — including western Kansas and parts of the Texas Panhandle — irrigation may simply become impossible within a few decades. "We're already seeing changes in both areas," said Bridget Scanlon, a senior research scientist at the University of Texas's Bureau of Economic Geology and lead author of the PNAS study. "These trends will only accelerate as water scarcity issues become more severe."

All this is bad enough, and I haven't even mentioned the drying impact that climate change is likely to have on the region. Even if that could somehow be removed from the equation — which it can't — the very nature of the American Southwest is working against us. That whole sweep of the continental U.S. has a history of mega-droughts that occurred well before the major settlements of the past century, before desert cities like Phoenix and Las Vegas rose from nothing and before the Central Valley became the water-thirsty agricultural powerhouse it is today. It's possible we might look back on the 20th century as an unusually wet period — and the settlements and agriculture we developed during those years may turn out to be manifestly unfit for a hotter, drier future.

So what can we do? We can start with the irrigation I saw driving through the Central Valley, where water is too often wastefully applied to the soil. Irrigation consumes 90% of the world's available freshwater resources, but as the population increases while water levels remain the same or less, we need to learn how to conserve. In arid Israel, for example, farms use just 1/10th the global average of irrigated water per acre through drip irrigation that involves applying water directly to plants drop by drop, yet the country still produces plenty of food despite the climate. We may also need to think about what we're growing — like the water-intensive alfalfa produced in dry southern California. The American West is changing, and we'll need to change with it.

• Bryan Walsh