Key takeaways
- Climate change and El Niño combined to set a global record for extreme rainfall in 2024, exceeding the historical baseline by 20%.
- Human-caused warming can explain 40% of the record rainfall, while El Niño and rare tropical warming in three different oceans play contributing roles.
- UCLA researchers see many parallels in the formation of the current and 2024 El Niños that suggest 2027 may set new records for global extreme rainfall.
Though strong El Niños have only occurred four times in as many decades, 2024's intense El Niño is already getting a sequel. New UCLA research shows that 2024 broke the record for extreme rainfall, with 40% of that increase tied to global warming — and conditions are ripe for a repeat.
"Between El Niño and climate change, 2024 set a global record for the number of days with heavy precipitation," said UCLA climate scientist and lead author Chad Thackeray. "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."
In 2024, the occurrence of global precipitation extremes was 20% higher than baseline, surpassing the strong El Niños in 1983, 1998 and 2016, said Thackeray, a researcher in the UCLA Department of Atmospheric and Oceanic Sciences and UCLA's Center for Climate Science.
In the new research, published Oct. 9 in Science Advances, UCLA scientists found that even as El Niño's influence waned in 2024, extreme rain continued globally due to climate change. In previous strong El Niño years, the bulk of the heavy precipitation occurred in the first half of the year, before largely dissipating as the tropical Pacific cooled in summer. Even as the Pacific Ocean cooled in 2024, the rain surged again, with extreme deluges peaking in August, the study found.
"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."
Depending on how abnormally warm the tropical Pacific becomes, an El Niño is classified as mild, moderate or strong. Since reliable satellite measurements began in 1979, scientists have data on only four strong examples of the weather phenomenon. Although the 2016 El Niño was stronger than 2024, it produced less rain, the research noted.
"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 UCLA climate scientist and senior author Alex Hall, director of the 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.
How ocean warming drove 2024's record rain
The study found that in 2024, El Niño could only explain 20% of the record rainfall, while global warming was tied to 40%. A portion of the remainder was tied to a rare event: Broad regions of the tropical Atlantic and Indian oceans were unusually warm at the same time that the Pacific Ocean warming triggered El Niño. The only other year with triple-ocean warming near this level was 1998, which held the record for extreme rain until 2024.
"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."
Regardless, researchers said their findings about 2024 suggest that another strong El Niño and ongoing global warming mean that 2027 is primed to break records again. In addition to climate change, warming in the Pacific Ocean appears to be coalescing in the eastern Pacific, which correlates with rainier seasons than central-Pacific El Niños, they said. Early scientific estimates project that 2027 will likely surpass 2024 as the hottest year on record, which will further amplify the atmosphere's sponge-like ability to absorb and drop more water.
"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.
