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Environment

A Devastating Drought in South America Was Caused by an Unusual Wave Halfway Around the World

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A devastating drought in eastern South America a few years ago caused catastrophic water shortages in parts of Brazil, disruptions in coffee and soy production, and a surge in mosquito-borne diseases. 

Now, a team of researchers traced the drought to an unusual wave originating thousands of miles away in the Indian Ocean. Their research, published Monday in the journal Nature Geoscience, shows how massive chain reactions can alter the planet’s climate system and warns against the growing consequences of climate change. Through their forensic analysis, the researchers hope that countries can better predict and prepare for future droughts. 

“The whole story, it’s all tied up to a common driver,” Regina Rodrigues, lead author of the report and professor of oceanography at the Federal University of Santa Catarina in Florianópolis, Brazil, told Global CItizen. “We used several scientific tools ... to find the most extreme droughts, and when we traced back [the information] we realized that there was this kind of wave pattern coming from the Indian Ocean.

“Once you know where these events come from, then you can monitor it, and that would give you better prediction ability,” she added. “That’s the ultimate goal.”

The drought started in 2013 when a powerful atmospheric convection, which happens when different temperatures collide in the atmosphere, erupted over the Indian Ocean. This caused a “planetary wave” to form in the ocean and travel to the South Atlantic. 

Once there, the warm mass of water interfered with local precipitation conditions, triggering an “atmospheric blocking” that prevented clouds from forming and releasing rain above Eastern South America. A feedback loop then formed as the lack of clouds caused more sunlight to fall on the ocean, creating an intensifying marine heat wave that further interfered with the surrounding climate. 

The resulting drought in parts of Brazil caused devastating health and economic impacts throughout 2014. 

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The prevalence of dengue fever, a potentially lethal mosquito-borne disease, tripled in the country because more people, in their desperation to have enough water, kept buckets of water out in the open, allowing mosquitoes to thrive. 

“You have all these small buckets of water everywhere, plus the high temperature, it’s perfect for the increase of mosquitoes,” Rodrigues said.

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Coffee farms, which are sensitive to climate shifts, took a major hit and worldwide prices of coffee rose. Soy production similarly declined. 

Mismanagement of water sources in cities like São Paolo, meanwhile, could no longer be ignored as the drought prevented replenishing rains from reaching critical reservoirs. 

The researchers looked at climate data from the past few decades and found similar patterns to suggest that the Indian Ocean has sent planetary waves to the Atlantic before, but there’s not enough data to definitively link the phenomenon to climate change, Rodrigues said. 

At the same time, the general warming of the oceans has been linked to climate change, because the oceans absorb the majority of excess heat trapped in the atmosphere by greenhouse gas emissions. As the oceans become hotter, extreme weather events become more likely because warm and cool pockets of air become more likely to collide.

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Rodrigues said that the next phase of research will be to examine how the heat wave affected marine life. Past research has shown that hotter ocean temperatures kill coral reefs and unravel marine ecosystems

Her team is working with 35 other institutions to explore this area of research as part of the European Union’s Project Horizon 2020.

“It’s important to try and understand the mechanisms of these events to predict the impacts on marine environments, which are already stressed by pollution, plastic and so many other things,” Rodrigues said.