Southwestern USA could be set for its worst drought in 1,000 years because of climate change. Numerous states have experienced severe water shortages, with 64 million people affected. Researchers say things could get worse.
The arid conditions in the southwest of the United States and the Great Plains have been caused by higher temperatures, while ground water supplies are shrinking. Studies by scientists using computer models show that the US could be in for its worst droughts since the 12th and 13th centuries.
“The 21st-century projections make the [previous] mega-droughts seem like quaint walks through the Garden of Eden,” said Jason Smerdon, who was a co-author of the paper, which was published in the journal Science Advances and is also a climate scientist at Columbia University’s Lamont-Doherty Earth Observatory.
Ben Cook, from NASA’s Goddard Institute for Space Studies, also helped to write the paper added that American’s may have to get used to droughts as a way of life.
These mega-droughts during the 1100s and 1200s persisted for 20, 30, 40, 50 years at a time, and they were droughts that no one in the history of the United States has ever experienced, he said in a press release.
“The droughts that people do know about like the 1930s ‘dustbowl’ or the 1950s drought, or even the ongoing drought in California, and the southwest today – these are all naturally occurring droughts that are expected to last only a few years or perhaps a decade. Imagine instead the current California drought going on for another 20 years,” Cook added.
To aid their research, the scientists sued data, which they retrieved from tree rings. They were able to determine how much precipitation had fallen and how much moisture was in the ground as the rings were wider during wetter years.
“The surprising thing to us was really how consistent the response was over these regions, nearly regardless of what model we used or what soil moisture metric we looked at,” Cook said in the press release.
It has long been accepted by scientists that the southwest and the Great Plains will become arid during the second half of the 21st century as a consequence of climate change. However, this process is being accelerated due to the increasing levels of carbon dioxide in the atmosphere.
Precipitation levels can be misleading the authors of the report said. Rainfall levels could remain the same as non-drought years, but an increase in temperature means more water is evaporated.
California saw record amounts of rainfall in December 2014, though this has not been enough to fill up water supplies across the state. Crucially, snowfall amounts have been low, which has made it difficult to replenish reservoirs and underground aquifers. NASA says satellite images show the Sierra Nevada range snowpack is half the amount of past estimates.