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Study: ‘Exceptional’ 2018 Drought Made Worse By Climate Change

U.S. Drought Monitor

In 2018 the Four Corners region suffered from an “exceptional” drought—the highest rating on the U.S. Drought Monitor’s scale. Water sources dried up and crops died, costing the U.S. economy 3 billion dollars. Scientists are now able to pinpoint how much of that drought was the result of climate change. KNAU’s Melissa Sevigny spoke with Emily Williams of the University of California-Santa Barbara, the lead author of the study.

Melissa Sevigny: You wanted to figure out how much of this drought was caused or attributed to climate change. How did you go about answering that question?

Emily Williams: There is a budding area in climate science. A lot of times people have probably heard the idea that with climate change we can’t look at any one single event and say whether or not it was caused by climate change. That isn’t true so much anymore. So there’s an area of research called “detection and attribution studies” that allows us to look at specific events—they could be droughts, they could be floods—and use various statistical tools to determine to what extent climate change exacerbated, made an event more intense or made it more likely. What we ended up doing, we decided we would just focus on how higher temperatures related to climate change exacerbated that drought.

What did you find out?

Our results were pretty surprising. Just looking at those hot temperatures, leaving aside the really low precipitation, we found that climate change reduced snowpack by about 20% and also contributed to about 20% of the poor rangeland and vegetation conditions.

You said that was surprising. What surprised you about that?

I think what was surprising we were looking at the record low year in terms of rainfall, but even leaving aside the fact rainfall was so low, those hot temperatures alone exacerbated it by 20 percent. What that showed to us was the fact that—you know, there’s always variability in the climate system. The Southwest is not new the idea of droughts. There have always been droughts, there have always been really wet years. But with climate change, every single year is that much hotter than the year before… Those hotter temperatures, what they do is they evaporate that much more water out of the soil. They melt snowpack that much faster, and as listeners know, snow is a really important water source for the Southwest. What that will do is take what would have been a mild or moderate drought and make it into a severe drought.

Why do you think it’s important to tease out these differences; ok, we know how climate change is affecting this particular event?

What I think is important about these kinds of studies is seeing that climate change isn’t just this projected thing that we think is going to happen in the future. It’s happening in the here and now and it’s hurting people today. So 20 percent, listeners might be thinking, that means 80 percent of the drought was driven by natural processes. If you live in this area, though, if you are using water sources in this area, if you are a rancher and your livestock need access to watering holes, if you are a farmer—particularly in that area there’s lot of tribes that use rain-fed agricultural practices—that additional impact really has measurable impacts on people today, on livelihoods, on economics and cultural parts of livelihoods…. It’s not this abstract thing, it’s not just about the coasts. It’s about ensuring that people are safe and healthy and have access to livelihoods…. A lot of times when people talk about climate change mitigation they say it’s too hard, it’s going to be too expensive. But what attribution shows it’s going to be even more expensive to not address climate change.

Emily Williams, thank you so much for speaking with me today.

Thank you for having me.


Melissa joined KNAU's team in 2015 to report on science, health, and the environment. Her work has appeared nationally on NPR and been featured on Science Friday. She grew up in Tucson, Arizona, where she fell in love with the ecology and geology of the Sonoran desert.
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