Amazon Wildfires May be Linked to More Hurricanes in the North Atlantic

First Posted: Aug 18, 2015 04:44 PM EDT

Researchers uncovered a disturbing link between wildfire risk in the Amazon basin and hurricanes in the North Atlantic. They've discovered that high wildfire risk may actually cause more devastating hurricanes.

"Hurricane Katrina is indeed part of this story,' said James Randerson, senior author of the new paper, in a news release. "The ocean conditions that led to a severe hurricane season in 2005 also reduced atmospheric moisture flow to South America, contributing to a once-in-a-century dry spell in the Amazon. The timing of these events is perfect consistent with our research findings."

In addition to the well-understood east-west influence of El Niño on the Amazon, there's also a north-south control on fire activity that's set by the state of the tropical North Atlantic. Warm ocean waters help hurricanes develop and gather strength and speed on their way to North American shores. They also tend to pull a large belt of tropical rainfall, known as the Intertropical Convergence Zone, to the north. This draws most of the moisture away from the southern Amazon and leads to heightened fire risk over time.

The mechanics of the ocean-fire link in the Amazon are fairly straightforward. When the North Atlantic sea surface temperatures are warmer than normal, less rain falls in the southern Amazon. As a consequence, groundwater is not fully recharged by the end of the rainy season. This means that plants can't evaporate and transpire as much water out through their stems and leaves. As a result, the atmosphere gets drier and drier, creating conditions in which fires can spread rapidly.

"Understory fires in Amazon forests are extremely damaging, since most rainforest trees are not adapted to fire," said Douglas Morton, one of the researchers. "The synchronization of forest damages from fires in South America and tropical storms in North America highlights how important it is to consider the Earth as a system."

The findings are published in the journal Geophysical Research Letters.