Climate Change Is Drying Out the American West

Picture a drought.

If you’re up on your American history, you’re probably imagining the Dust Bowl crisis of the 1930s—a decade-long drought that combined with poor land management practices to trigger one of the largest migrations in U.S. history. Oklahomans and other Plains farmers headed west in desperate search of work, and the associated economic convulsions were a major contributor to the Great Depression. The Dust Bowl is branded into our cultural memory as the defining American drought.

But if you think the Dust Bowl was American drought at its worst, think again. According to new research published in the Proceedings of the National Academy of Sciences, the droughts experienced so far in the 21st century surpass the Dust Bowl. And the worst is yet to come.

The new study, conducted by a team of government and university scientists, examined tree ring data from the past 1,200 years. The width and density of a tree ring tell us how much water was available in the year it formed—wider rings, for example, indicate that ample water spurred rapid growth, while narrow rings suggest that dryness inhibited the tree’s growth. Using this data, combined with other climate indicators, the researchers were able to reconstruct the volume of water flowing through the rivers and streams in the Upper Missouri River Basin going back to pre-Columbian times.

They found that the drought that spanned 2000 to 2010 surpassed the Dust Bowl and likely rivaled the worst droughts in the upper Midwest, stretching back more than a millennium.

Human carbon emissions are the leading cause of the worsening U.S. droughts, and they drive the phenomenon in several ways. The most obvious is temperature: Hot air absorbs more water. So, as the temperature of the air warms due to climate change, it draws more water out of lakes, rivers, soils, and plants. In addition, when the atmosphere is warm, precipitation is more likely to fall as rain than as snow. That’s a problem, because snow helps dry areas retain moisture, and when it melts, the meltwater flows across soils when they are more likely to need it. The lack of snow cover also causes the land to absorb more sunlight and further accelerate the warming process.

It would be easy to think of this research as another of those “everything is a bit worse with climate change” studies. Hurricanes are a bit stronger. Extreme heat is a bit more common. Sea levels are a bit higher.

The thrust of this study, however, isn’t that droughts are a bit worse, or even a lot worse. This finding invites us to think of drought differently—not as a periodic lack of precipitation but rather as a progressive drying out of the landscape. The authors say we will continue to experience periods of acute crisis, followed by moments of relief, but the overall trend is clear. The United States, particularly, the West, is becoming ever more arid. Climate change is wringing out our country like a sponge.

Policy makers and the public currently view the end of an acute drought as an opportunity to return to normalcy—showers get longer, cars get washed, farmers irrigate crops freely, and restaurants fill your glass before you ask. But that response is badly misguided. Droughts aren’t things to be overcome—they are harbingers of a new normal in which our water demand perpetually outstrips our water supplies.

And that requires not only rethinking our relationship to water use but taking urgent action against climate change and the carbon emissions that fuel it. Measures to conserve water and curb carbon emissions will be crucial to prevent this drying out from intensifying.

“Unfortunately, climate change and this aridification are likely irreversible on human timescales, so the sooner emissions of greenhouse gases to the atmosphere are halted, the sooner the aridification of North America will stop getting worse,” write Jonathan T. Overpeck of the University of Michigan and Bradley Udall of the University of Colorado Law School in a commentary accompanying their study.

But if action isn’t taken, in addition to losing water to green lawns and almond trees, the land will lose its moisture to the atmosphere and to the oceans on an unimaginable scale.

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