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The Science Behind the U.S. Drought

This post is part of WRI's "Extreme Weather Watch" series, which explores the link between climate change and extreme events. Read our other posts in this series.

Heat and drought continue to blanket the United States, leaving 54 percent of the nation’s pasture and rangeland, 38 percent of its corn crop, and 30 percent of soybeans in “poor” or “very poor” condition. As of the end of June, 55 percent of the contiguous U.S. was experiencing moderate or extreme drought – the most extensive drought in more than half a century (see map from last week’s US Drought Monitor).

What’s Causing the Drought?

What we know is that recent temperature and precipitation levels have strayed significantly from historical averages (with, for example, 2012 being the warmest spring ever experienced in the U.S. since record keeping began in 1895). From the Southwest to the Great Lakes, temperatures have been so high and rainfall so low that the drying effect of warmer air temperatures far exceeded what little precipitation there’s been, resulting in moisture being drawn out of soils. This situation has occurred at a critical time in the country’s growing season, leaving the ground sapped of moisture and, in turn, wreaking havoc on crops and livestock. According to the National Oceanic and Atmospheric Administration (NOAA), even if a normal amount of rainfall occurred this year, it could not have offset the drying effect of the record-breaking heat.

In addition, recent warming across a large swath of the nation led to faster melting of already-reduced snowpack, which supplies water bodies as it melts. This has resulted in below average spring and early summer runoff and depleted reservoirs. For example, this year’s water flow to Lake Powell, which straddles the border between Arizona and Utah, is projected to be less than 50 percent of the average flow.

<p>Credit: U.S. Drought Monitor</p>

Credit: U.S. Drought Monitor


Is There a Climate Change Connection?

So what explains these patterns? One factor could be La Niña conditions, which leads to shifts in weather patterns and can contribute significantly to drought in the Southwest. But it’s also important to note, as our colleagues at Climate Central explain, that these dry, hot conditions are occurring against a backdrop of human-induced climate change. Research shows that global warming intensifies both drought and heat, making drought even dryer and heat waves even warmer than they otherwise would have been without excess greenhouse gases in the atmosphere.

What Does the Research Say About Climate Change’s Future Impacts?

According to the U.S. Global Change Research Program (USGCRP), we will see more severe and frequent drought events in the U.S. if human-induced climate change continues unabated. This drought will coincide with rising temperatures, further straining water availability.

Declines in precipitation and increases in summer temperatures are projected for the Southwest in particular. This combination of effects will lead to “a serious water supply challenge in the decades and centuries ahead,” according to the USGCRP. Research indicates that the Great Plains, the nation’s breadbasket, with agriculture covering 70% of the region, will also witness rising temperatures and evaporation rates, as well as more sustained drought. Optimal growing zones will likely shift, affecting farmers, and pests are likely to come earlier given milder winters, resulting in greater numbers of insects.

What Do We Make of This?

Climate science is advancing in its ability to attribute individual extreme events to climate change. For example, a new NOAA report analyzed recent extreme events’ connections to climate change and found that the conditions leading to the 2011 Texas drought are 20 times more likely to occur now than in the 1960s due to increases in greenhouse gas concentrations and the resulting climatic changes. And it’s likely we’ll soon learn even more; the recent heat waves and drought will undoubtedly be the focus of intense scientific study in the coming years.

But we don’t need to wait for more scientific literature to know that the conditions we’re currently experiencing match projections of a warmer world. As U.S. politicians swelter while addressing the losses this drought is bringing to our economy, it’s time they also adopt a policy agenda that will reverse our carbon-intensive ways. Otherwise, this current drought will just be a taste of what’s to come – and come more often.

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