Behind the Forecast: Study finds parts of the US in potential megadrought

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Science Behind the Forecast: Megadroughts

LOUISVILLE, Ky. (WAVE) - An April 17, 2020 study has raised concerns about a blossoming megadrought in the Western United States. Researchers used dozens of climate models, tree-ring data stretching back 1,200 years, and modern weather observations for their study. The study's analysis covered nine states, stretching from parts of northern Mexico into California and New Mexico and up to Oregon and Montana. According to the authors, this megadrought could be just as bad or even worse than anything seen in history.

What is a megadrought? It is a drought event of unusual severity lasting for at least 20 years, according to Smithsonian Magazine.

Since reliable modern observations only date back to around 1900, scientists had to use tree rings to infer yearly soil moisture content for the periods before humans started to influence the climate.

The U.S. Drought Monitor indicates 69 percent of the state is experiencing dry or drought conditions. (Source: Pixabay.com)
The U.S. Drought Monitor indicates 69 percent of the state is experiencing dry or drought conditions. (Source: Pixabay.com) (Source: Pixabay.com)

Using data from thousands of trees, found thousands of droughts throughout history. Four were megadroughts that lasted decades: during the late 800s, the mid-1100s, the 1200s, and the late 1500s. These were compared to soil moisture records from 2000 to 2018. They found that the current drought was outpacing the three earliest megadroughts. They also determined that this megadrought was affecting a larger area of land more consistently than any of the previous droughts; they blame global warming for this fact.

It's important to note that nature was the main driver for the previous megadroughts, and the one that the study says is ongoing.

A 2019 study found that La Nina, which is unusually cool conditions over the tropical Pacific Ocean, shifted the tracks of storms further to the north, depriving parts of the western U.S. of much-needed precipitation during previous megadroughts. Average temperatures in the western United States have risen 2.2°F since 2000, playing a role in the precipitation deprivation. Hotter air holds much more moisture; since that moisture has to come from somewhere, it is often pulled from the ground, thus intensifying the dryness of the soil.

Researchers say that hotter temperatures are responsible for half of the severity and pace of the ongoing drought. Basically, researchers state that without our warmer climate, this may have been a regular drought and not a megadrought.

There are quite visible effects of the drought. Lakes Mead (Nevada and Arizona), and Powell (Utah and Arizona), a vital source of water for agriculture, have significantly shrunk. Wildfires across the Western United States have been covering more area.

Many locations in the western United States, as of April 21, 2020, were dealing with some level of drought.
Many locations in the western United States, as of April 21, 2020, were dealing with some level of drought. (Source: U.S. Drought Monitor)

As of April 23, 2020, only a sliver of northern California and southern Oregon are experiencing an Extreme Drought, according to the United States Drought Monitor. There were quite a few locations across the western U.S. that were dealing with a moderate or severe drought.

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