A busy Atlantic hurricane season could mean more fires in the Amazon
While warm ocean water drives hurricanes to the U.S. East Coast, the Amazon is likely to feel the heat.
The 2020 fire season in the Amazon rain forest could be far worse than in 2019, researchers say, partly because of the same climate conditions that are fueling an active hurricane season to the north.
Last August, a spate of enormous, human-set fires in the Amazon sent smoke billowing over the Brazilian city of São Paulo, turning day into night and prompting an international outcry. But while those fires were unusual and alarming, the situation could have been far worse if the Amazon had been in a drought.
Unfortunately, drier-than-average conditions are exactly what’s being forecast for the southern Amazon this year, thanks in part to an unusual buildup of heat in the tropical North Atlantic, thousands of miles away.
That oceanic heat has also caused the Atlantic hurricane season to get off to a record fast start, a harbinger of what is predicted to be an unusually busy season. Some research suggests a causal link between hurricanes themselves and bad Amazonian fire years — although that is a matter of greater debate.
“What I think is happening is the ocean is forcing both of those conditions,” says Chris Landsea, a research meteorologist with the National Oceanic and Atmospheric Administration’s National Hurricane Center. “It’s forcing active Atlantic hurricane years, and at the same time causing fires to be likely in the Amazon.”
A perfect firestorm
Doug Morton, a NASA Earth scientist who co-created a seasonal fire forecast for the Amazon, says the rain forest faces the “perfect storm” of conditions for fire this year. Those include a ramp-up in deforestation—a key driver of fires in the Amazon—and broader patterns in the oceans and atmosphere that could lead to drought.
During the first six months of 2020, an estimated 1,184 square miles of forest were deforested—a 25 percent increase compared with the first half of 2019. Jos Barlow, a conservation scientist at Lancaster University, says if the accelerated pace of deforestation continues, nearly 6,000 square miles of forest could be logged by the end of the year, since the most intense logging season is now commencing. That would mark the highest rate of deforestation since 2005.
Amazonian landowners typically set fires to clear land for ranching and farming, although many fires are also set in public forests by people attempting to claim new land. “I’m afraid everything points to this being another very bad year for deforestation,” Barlow wrote in an email. “And unlike 2019, these clearance fires used to burn the felled forests are likely to be aggravated by a drier-than-usual climate,” meaning they could grow faster, become harder to control, and even escape into virgin rainforest.
Indeed, seasonal forecasts indicate large swaths of the Amazon could be plunged into drought as the dry season, which began in June and runs through November, progresses. That’s due, in part, to ocean temperatures far to the north, which form a key part of the basis for Morton’s fire forecast.
According to Yang Chen, an Earth scientist at the University of California, Irvine, who developed the forecast with Morton, temperatures in the tropical North Atlantic are currently “way above average.” When that part of the ocean is especially warm, it triggers a northward shift in the Intertropical Convergence Zone, a belt of low-pressure air that delivers intense, rainmaking thunderstorms to the tropics. If this rain belt shifts further north ahead of the southern Amazon’s dry season, it causes the dry season to start earlier and be even drier than usual.
“In previous years, when the tropical north Atlantic Ocean was warm — in 2005 and 2010 — that triggered record droughts across the Amazon,” Morton explains. “And with those droughts came fires.”
A direct link to hurricanes?
Warm tropical North Atlantic waters also fuel hurricanes, which sends moisture to the west and then north on prevailing winds instead of south. In fact, research that Morton and Chen published in 2015 shows that active Atlantic hurricane seasons and severe Amazonian fire seasons go hand in hand. While both phenomena correlate with heat in the tropical North Atlantic, they correlate more strongly with one another.
Morton believes that indicates a causal link between the two. When tropical storms and hurricanes form, he says, “they take the moisture that would otherwise flow onto the South American continent... and drive it toward the Gulf Coast and eastern seaboard of the United States. Essentially, it’s taking moisture away from the Amazon.”
Chen is less convinced that Atlantic hurricanes trigger drought in the Amazon directly, although he agrees that both “share the same reason,” namely, excessive heat in the tropical North Atlantic and its impact on weather patterns.
Landsea, of the National Hurricane Center, is also unconvinced of a direct causal link between greater numbers of Atlantic hurricanes and Amazon drought. He points out that hurricanes are “very transient events. They only last for a few days, and only account for a small percentage of the rainfall in the Carribean.” But he agrees that there’s “certainly an association” between the two phenomena.
Either way, the 2020 hurricane season should serve as a red flag for the Amazon : There have already been six named tropical storms in the Atlantic, a record for this point in the season, which only began on June 1. And hurricane activity is expected to ramp up as summer wears on and heat builds across the tropical Atlantic.
“We are anticipating it to get very busy,” Landsea says.