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Megadrought in the USA
30.4.2020
Translation: machine translated
It has been extremely dry in the USA for 20 years. The situation is comparable to the four mega-droughts of the last 1200 years, say researchers. It may even be worse.
The USA could be in the midst of a megadrought of unprecedented proportions. At least that's what a study by scientists led by Park Williams from Columbia University has now published in the journal "Science" suggests.
Since most climate records only go back to around 1900, the researchers analysed the rings of thousands of trees in an area that spanned nine different US states, from Oregon and Montana to California, New Mexico and the northern parts of Mexico. In this way, they collected information on soil moisture and thus on the dry periods of the past 1200 years or so.
Since the year 800 AD, Williams and his colleagues have recorded exactly four so-called megadroughts with periods of drought that lasted for decades: In the late eighth century, the eleventh century, the twelfth and finally one in the late 1500s. There have been no more such events since 1600: until now!
Only 1575 was worse - perhaps
In the next step, the researchers compared the data from the four historical megadroughts with soil moisture records from 2000 to 2018, when it was also extremely dry in parts of the USA. They discovered that the current dry period had already eclipsed the three early megadroughts. Only the extreme drought that prevailed from 1575 to 1603 was probably slightly worse. However, the differences are so small that this cannot be said with certainty, the researchers explain. The current dry period is also affecting larger areas of the country.
The researchers attribute this development to global warming, among other things. The average temperature has risen by 1.2 degrees Celsius since 2000. And as warmer air can absorb more moisture, less of it remains in the soil. However, weather events such as La Niña over the Pacific could also have played a role, as was the case with the earlier megadroughts.
As the extreme droughts of the past have all lasted longer than 19 years, scientists assume that the current drought in the USA will also continue for a while. We can only hope that it will not be as long as the mega-drought that began in the 1200s, which lasted for almost a century.
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