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Deeper Droughts Possible In Southwest, Scientists Warn

University of Nevada-Las Vegas

The Colorado River Basin is enduring two decades of drought, and water shortages are on the horizon. But scientists say this isn’t the worst-case scenario. The region has undergone longer, deeper droughts in the past. KNAU’s Melissa Sevigny spoke with paleoclimatologist Matt Lachniet of the University of Nevada-Las Vegas about how knowing the past can help us plan for a warmer, drier future.

Tell me about how this current drought compares to droughts that the region has seen in the past.

Well, we know from tree ring records that go back the last 1,500 years or so, that nature is capable is giving us droughts that last for 10, 15 years or so, and some of them were pretty severe, similar to what we’re seeing today…. But there’s a fundamental difference, and that fundamental difference is that climate is warming in the Southwest and regionally… Warming climate means less of that rainfall falls as snow. It means more evaporation from the reservoirs, and it means the plants themselves are using more water.

So are you saying that what we’re experiencing now—is there a better word than drought? It sounds like it’s something we’re going to be dealing with as long as we’re dealing with climate change.

So long as the region continues to warm, we’re going to be trending into what climate scientists would call aridification. We can hope that natural climate cycles will push us back into wetter conditions that will somewhat offset the drier conditions associated with the warming, but we don’t really have any evidence that that’s going to happen. It’s wishful thinking at this point. … Our job as paleoclimatologists, looking into the past, is to see what nature is capable of in even longer time intervals. The reason this is important, is because when we look further back in time, past the tree ring records, we look at geologic archives of climate change, like lake levels, or cave deposits which I study, or packrat middens, and what they are showing us is the Southwest can be in an extended period of aridity for hundreds to perhaps even thousands of years.

One way you’ve studied these droughts is by looking at caves, is that right? How does that work?

I used cave deposits that are called speleothems. Speleothems consist of stalactites and stalagmites and other features. I mostly focus on cave stalagmites. They grow upward over time by depositing a thin layer of limestone bit by bit as water drips from the celling of the cave onto these stalagmites. They essential grow over time. We’re able to date the intervals of growth, find out how old this material is, and then we measure the chemistry within those cave deposits to understand something about climate change. Because the chemistry of the limestone varies as a function of climate, we’re able to reconstruct what’s happened thousands of years into the past, going back upwards to 100,000 years of climate history for the Southwest.

So knowing that, having this information from the past that shows us it could get a lot worse than it is now, how can that information help policymakers make decisions about what to do next?

The first thing is to acknowledge that nature is capable to being even hotter and drier than it today, and it’s capable of having arid intervals more arid than today last for thousands of years. The challenge for policymakers is not only to recognize the scientific fact, but figure out how to change the policies to have the flexibility to potentially adapt to those future conditions should the aridification we’re currently seeing continue into the future.

I really appreciate your time, thanks so much.

Thank you.

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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