NASA and University of California, Irvine researchers have uncovered a strong link between high wildfire risk in the Amazon basin and devastating hurricanes in the North Atlantic Ocean.
The findings are published in the journal Geophysical Research Letters about 10 years after Hurricane Katrina ravaged New Orleans.
“Hurricane Katrina is, indeed, part of this story,” said UCI Earth system scientist James Randerson, senior author on the paper.
“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 perfectly consistent with our research findings.”
Brian Bell of the University of California, Irvine, reported on the study on the NASA website:
Lead author Yang Chen discovered that in addition to the well-understood east-west influence of El Niño on the Amazon, there is also a north-south control on fire activity that is set by the state of the tropical North Atlantic. The North Atlantic has two modes. In years of high numbers of hurricanes and high fire risk, warm waters in the North Atlantic 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, Chen said, drawing moisture away from the southern Amazon.
As a consequence, ground water is not fully replenished by the end of rainy season, so coming into the next dry spell, when there is less water stored away in the soils, the plants can’t evaporate and transpire as much water out through their stems and leaves into the atmosphere. The atmosphere gets drier and drier, creating conditions where fires can spread rapidly three to six months later. Ground-clearing fires set by farmers for agriculture or new deforestation can easily jump from fields to dense forests under these conditions.