The "megadroughts" of the Middle Ages could return due to the warming effects of climate change, a new study says.

Scientists said the prolonged droughts have been absent in the American Southwest since the 16th century, but researchers studying past megadroughts predict they may soon plague the region again, according to the study published Wednesday in Science Advances.

Without access to weather records before the late 1800s, researchers used "proxy data," including tree rings and lake sediment, to analyze how much rain fell, USA Today reported.

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Before the study, researchers said it was a mystery as to what caused the megadroughts or why they stopped centuries ago.

"In our paper, we present the first comprehensive theory for what caused historical megadroughts, which happened during the medieval period but not after about the year 1600," study lead author Nathan Stieger of Columbia University's Lamont-Doherty Earth Observatory told USA Today. "We find that they were caused by severe and frequent La Niñas, a warm Atlantic Ocean, and a net increase in energy from the sun."

Climate change could be increasing the possibility of megadroughts returning, he said.

"Because you increase the baseline [dryness], in the future when you have a big La Niña, or several of them in a row, it could lead to megadroughts in the American West,” Steiger told the paper.