Science

“Megadrought” to hit USA in coming months

Cracked ground: Tomas Castelazo (Via wikimedia commons)

By Kirstin Winter

Despite widespread lockdown providing a small respite for the climate, the Southwestern North American region (SWNA) is predicted by scientists to enter a period of “megadrought”. 

Since the coronavirus outbreak, pollution levels have been dropping all over the world. In New York, carbon monoxide levels had been reduced by 50% since last year and, in China and Northern Italy, nitrogen dioxide levels have also fallen. 

Despite this, there are predictions that in the SWNA, summer droughts will intensify as the expected spring precipitation falls for 2020. There is some suggestion that the megadrought has already started; 2000 to 2018 was the second driest period since 800CE. However precipitation levels in 2019 did not reflect this. 

Since 1900, reliable weather records have been kept, allowing scientists to analyse precipitation levels. A report published by scientists at Colombia University predicted this “megadrought” and used tree rings to determine soil moisture levels since 800 CE. There is a relationship between the number of tree rings and the soil moisture content.  Soil moisture levels are indicative of the precipitation levels, allowing scientists to draw accurate conclusions about when droughts have occurred in the past. 

In the 1200 years analysed in this study, the 20th century was one of the wettest on record, causing misconceptions regarding drought risk.

Droughts and fluctuations in precipitation levels in the past have been attributed to natural causes, for example, cooling ocean temperatures blocking storms over the U.S. 

The 2020 “megadrought” is likely to be exacerbated by human activity and the subsequent global warming; “What matters is that it has been made much worse than it would have been because of climate change” explains Benjamin Cook, an environmental scientist at Colombia University. 

According to Park Williams- bioclimatologist at Colombia University- “we’re on the same trajectory as the worst prehistoric droughts”.  Temperature rises of about 1.2 degrees are causing changes in the climate across the globe. The report published in Science attributes 47% of the drought severity between 2000 and 2018 to anthropogenic trends. Droughts are expected to be a lot more severe in terms of longevity, widespread location and frequency.

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