Climate change helped fuel record levels of extreme rainfall worldwide in 2024, and similar conditions developing during the current El Niño could lead to another record for heavy precipitation in 2027, according to UCLA research highlighted by the university Monday.
Researchers found that the frequency of extreme rainfall events in 2024 was 20% above the historical baseline, with human-caused global warming accounting for about 40% of the increase and El Niño contributing another 20%.
The findings, published in the journal Science Advances, suggest that the combination of a strong El Niño and continued global warming could produce another record-breaking year for heavy precipitation.
“Between El Niño and climate change, 2024 set a global record for the number of days with heavy precipitation,” said UCLA climate scientist Chad Thackeray, the study’s lead author. “We’re getting into uncharted territory for how warm the coming El Niño is going to be, but the conditions are there for another record in 2027.”
The study found that extreme rainfall in 2024 surpassed levels recorded during previous strong El Niño years, including 1983, 1998 and 2016.
Unlike those earlier events, when heavy precipitation generally diminished as the tropical Pacific Ocean cooled during the summer, extreme rainfall continued across much of the globe in 2024 and surged again in August, according to the researchers.
“That surge in 2024 is largely tied to climate change,” Thackeray said. “Compared to El Niños of the ’80s and ’90s, we now have baked in decades more of warming. A warmer atmosphere can hold more moisture, which can mean more severe rainstorms, and the chance of heavy rainfall is increasing over time. By midcentury, we would expect extreme rainfall like what we saw in 2024 almost every other year.”
Researchers said a rare combination of warming in the tropical Atlantic, Indian and Pacific oceans also contributed to the 2024 rainfall record.
The only other year with comparable warming across all three ocean regions was 1998, which held the previous record for extreme rainfall, according to the study.
“That concurrence is quite rare,” Thackeray said. “Our analysis relied on ocean temperature measurements from December to February each year when El Niño is strongest, so we don’t yet know whether that will be a factor this upcoming year.”
Scientists classify El Niño events as mild, moderate or strong depending on how much warmer than normal the tropical Pacific Ocean becomes. Only four strong El Niño events have occurred since reliable satellite measurements began in 1979, according to the researchers.
Although the 2016 El Niño was stronger than the 2024 event, it produced less extreme rainfall, underscoring the increasing influence of global warming, the study found.
“In 2024, the year began during a strong El Niño, but unlike previous major El Niño years, the extreme rainfall was unusually widespread globally and persisted even after El Niño faded,” said climate scientist Alex Hall, the study’s senior author and director of the UCLA Center for Climate Science and the Institute of the Environment and Sustainability. “The record rainfall wasn’t simply the result of El Niño. Climate change transformed the backdrop.”
Researchers said the El Niño currently developing in the tropical Pacific is expected to peak this winter and could become one of the strongest on record.
They also noted that warming is developing in the eastern Pacific, a pattern associated with rainier conditions than El Niño events centered farther west.
Early scientific estimates suggest 2027 could surpass 2024 as the hottest year on record, potentially allowing the atmosphere to hold even more moisture and increasing the likelihood of extreme rainfall, according to the researchers.
“The El Niño now developing is expected to peak this winter and could become one of the strongest on record,” Hall said. “Our results show that a strong winter El Niño can prime the global atmosphere for elevated extreme precipitation well into the following year. And today’s warmer climate makes it easier to reach the kinds of extremes we saw in 2024.
“We can’t say that 2027 will break the 2024 record. But the ingredients are lining up for another potentially exceptional year for global precipitation extremes.”
The research was funded in part by the National Science Foundation and the U.S. Department of Energy.