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One-in-100-year drought linked to deforestation, climate change

South America’s Amazon and Nordeste regions are naturally prone to dry conditions, but a recent study suggests the drought of 2015-16 was caused by more than the usual oceanic forcing renowned for impacting the country’s weather patterns.

The study assessed the connection between sea surface temperatures and the 2015-16 drought, finding that human impacts, including deforestation and greenhouse gas emissions, may have had a part to play in the severity of the event.

Co-author and University of Connecticut Professor Guiling Wang said the study was motivated by the new frequency of intense drought in the region, coupled with a curiosity about potential influences.

“This is a region that has been on my radar screen for a while. My interest has significantly grown over the past 10 years as a result of the 2005 and 2010 droughts, both of which were said to be one-in-100-year events. Since then I have kept a close watch on the hydroclimate conditions in South America,” Wang said.

“Following 2010, there were several moderate drought years for some portions of South America, but the 2016 mega drought was mind-boggling. It was more extensive and more intense than both the 2005 and 2010 droughts.

“To have three one-in-100-year drought events within 11 years is quite remarkable. That’s what motivated us to try to figure out what might have happened.”

Although warmer sea surface temperatures in the Pacific and Atlantic oceans are responsible for previous droughts in the region, Wang said these factors alone could not account for the severity of the 2015-16 drought.

“Warming in the Pacific [El Nino] and in the Atlantic have long been considered the main cause of droughts in the Amazon, and they explain both the 2005 and 2010 droughts,” he said.

“We therefore started off with the oceanic forcing, and tried to relate the drought severity and extent to sea surface temperature in those oceanic basins.”

Although more research needs to be done to find evidence, Wang said the extent of the 2015-16 drought was likely fuelled by human activity.

“Several factors tend to reduce precipitation in South America, including oceanic forcing over the Pacific and Atlantic, deforestation, and greenhouse gas warming,” he said.

“Since oceanic forcing could not fully explain the severity and extent of the 2015-16 drought, deforestation and/or greenhouse gas warming likely have contributed to the drought. However, this remains a speculation until we show more clear evidence from carefully designed attribution experiments.”

Wang also suspects that if there is evidence to show these human-made factors are driving the severity of drought in the region, the region can expect more intensely dry periods more frequently in future.

“If deforestation or greenhouse gas warming has become significant enough to cause substantial decrease of precipitation, we can expect severe droughts to become more frequent in the future,” Wang said.

Take a look at the full study here.