On paper The Amazon rainforest is a static space: constantly wet, impenetrable, constantly filled with biology. But in reality, the region endures periodic droughts when rains decrease, trees dry up, and wetlands dry up. Boom and crash. As with forests around the world, this is part of the natural order.
One of the drivers of drought in the Amazon could soon set in, which could put even more pressure on an ecosystem already devastated by deforestation and human-caused fires. El Niño Southern Oscillation a phenomenon in the Pacific Ocean in which a band of water forms off the coast of South America that changes from neutral to exceptionally cold or warm. Cold La Niña conditions have been easing in the past few years, potentially giving way to warm El Niño conditions later this year. modeling National Oceanic and Atmospheric Administration. And for the Amazon, it can cause drought.
It is still too early to say when El Niño will come and how serious it could be. But scientists remember how bad things were during El Niño eight years ago. “In 2015-2016. observable that the air temperature over the Amazon was the hottest in perhaps the last century,” says Juan Carlos Jiménez-Muñoz, a physicist and remote sensing specialist at the University of Valencia. “In particular, over the Amazon [El Niño] suppresses rain, and a general drought can be expected.” But, Jimenez-Muñoz warns, “every El Niño is unique—you can have different regional or local effects.”
This is due to the fact that El Niño greatly changes the atmospheric circulation. When this warm water drop forms in the Pacific Ocean, it creates more evaporation, sending moist air into the sky. This water eventually falls as rain over the ocean. It gets in the way Walker circulation, causing relatively dry air to drop over South America, resulting in less rain over the Amazon. “In general, rain falls more on the ocean,” says Earth systems specialist James Randerson of the University of California, Irvine. “It’s just that there isn’t much rain on earth. Continents are losing water, especially South America.”
When El Niño is inactive and conditions are normal, moisture evaporates from the Amazon and rises into the sky before falling to the forest as rain. In this way, the Amazon can recycle up to half of its rainfall. “The Amazon is a factory for atmospheric moisture,” says Paola A. Arias, a climate scientist at the University of Antioquia in Colombia. “When you have droughts, you also typically have reduced rainfall recycling.”
Because El Niños vary in magnitude, they differ in how rain suppression occurs over the Amazon. They also differ in exactly where they cause drought and for how long. If El Niño development is more concentrated in the central Pacific, it tends to create a drought centered in the northeastern Amazon. If it is more concentrated in the eastern Pacific, the drought may be more widespread and last a little longer. But as for 2023, it’s still too early to tell how it all plays out – Randerson says scientists should have a better idea this spring. “The fact that we’re in this sustained La Niña for so long,” Randerson says, “I think it’s more likely that you will move into a stronger El Niño state.”