Over 75% of Tropical Forests Faced Extreme Drought and Heat in the 2023-24 El Niño
A new study in the journal Earth's Future found that over 75% of the world's tropical forests (about 77% by one measure) faced "compound" hot and dry conditions (drought and heat at the same time) during the 2023-24 El Niño, lasting about six months on average.
The study used climate data from 2000 to 2024 for about 15.9 million sq km of tropical forest across the Americas (8.4 million sq km), Africa (3.6 million sq km) and Asia (3.9 million sq km).
The worst hit were the Americas and Africa: compound hot-dry events covered about 88% of forests in the Americas and 89% in Africa, compared with about 43% in Asia. In the Americas they lasted about nine months.
Compared with the 2015-16 El Niño, heat lasted 10 to 13 months longer. About 80% of the dry, hot months fell in the wet season, when soils normally refill with water. Burned area rose by about 9%.
Projections suggest that under high emissions, years as hot as 2023-24 could happen every year from as early as 2043, and such conditions could become the "new normal" for tropical forests within about 20 years.
The authors warn that rising tree deaths could weaken the tropical forest carbon sink (about 1.2 billion tonnes of carbon absorbed each year) or turn parts of it into a carbon source.
El Niño–Southern Oscillation (ENSO)
El Niño–Southern Oscillation, or ENSO, is a natural climate swing in the tropical Pacific Ocean. In its warm phase, El Niño, the central and eastern Pacific becomes unusually warm; in its cold phase, La Niña, it becomes unusually cool. These swings change rain and temperature patterns across the world, including over India and the tropical forests of South America, Africa and Asia.
The study shows how El Niño, added on top of global warming, pushed most tropical forests into long spells of drought and heat at the same time. Future El Niño years will start from an even warmer base.
Compound Drought and Heatwave (CDHW) Events
A compound drought and heatwave event is when a place suffers a drought (a long shortage of water) and a heatwave (unusually high temperatures) at the same time. Each alone is harmful. Together, they make each other worse, so the damage to crops, forests, water supply and human health is far greater than the two would cause separately. Scientists call such linked disasters "compound events".
The study measured exactly this kind of event across the tropics. About three-fourths of tropical forests had drought and heat together for months, mostly in the wet season, when forests normally store water for the dry months. That makes the next dry season even more dangerous.
Tropical Forests as a Global Carbon Sink
A carbon sink is anything that takes in more carbon dioxide from the air than it gives out. Tropical forests, the dense forests near the equator, are among the world's most important natural carbon sinks. Their trees pull carbon dioxide out of the air and store the carbon in wood, roots and soil. By doing this, they slow down global warming.
The study found that hot, dry conditions in 2023-24 hit about three-fourths of tropical forests, raising tree deaths, fires and forest degradation. If such years become normal within 20 years, the forests that absorb about 1.2 billion tonnes of carbon a year could absorb far less, or even start releasing carbon, making global warming worse.
- Study: Earth's Future; data from 2000 to 2024; about 15.9 million sq km of tropical forest
- Share of tropical forests with compound hot-dry conditions in 2023-24: over 75% (about 77%), average about six months
- Compound hot-dry area: Americas about 88%, Africa about 89%, Asia about 43%
- Drought-affected forest area: about 80% overall (Americas 91%, Africa 92%, Asia 48%)
- About 80% of dry, hot months fell in the wet season; burned area up about 9%
- Heat lasted 10 to 13 months longer than in the 2015-16 El Niño
- Under high emissions, 2023-24-like years could occur every year from as early as 2043
- Tropical forests absorb about 1.2 billion tonnes (1.2 Pg) of carbon per year
- WMO: 2024 warmest year on record, about 1.55°C above pre-industrial