UCLA study links 2024's record heavy rainfall to warming and El Niño

UCLA researchers reported on October 12 that global heavy-precipitation extremes occurred at a record rate in 2024, with warming contributing to the increase alongside El Niño. The study, published in Science Advances on October 9, raises the possibility of another exceptional year in 2027 as a new El Niño strengthens, but its lead author says a repeat rainfall record cannot be predicted.

The researchers found that global precipitation extremes occurred 20% more often in 2024 than the baseline used in their analysis. That put 2024 above the strong El Niño years of 1983, 1998 and 2016. The measure concerns how often extreme precipitation occurred globally; it does not mean rainfall increased by 20% everywhere or that each region experienced the same conditions.

How warming and El Niño contributed to 2024's rainfall

The study attributed 20% of the record occurrence of heavy rainfall to El Niño and 40% to global warming, according to UCLA's account of the research. The report associated some of the remaining contribution with unusual warmth in the tropical Atlantic and Indian oceans at the same time as Pacific warming. Those figures describe the researchers' assessment of the 2024 global result, rather than a forecast for any individual country or storm.

The timing also distinguished 2024 from earlier strong El Niño years. In those previous years, most heavy precipitation occurred in the first half of the year. In 2024, the extremes continued after the Pacific cooled in summer and reached another peak in August. The researchers noted that the 2016 El Niño was stronger than the 2024 event but produced less rain, another reason El Niño strength alone cannot explain the record.

What NOAA's October El Niño outlook shows

An October 8 discussion from NOAA's Climate Prediction Center provides a separate check on current conditions. NOAA said El Niño continued to strengthen, with Niño-3.4 sea-surface temperatures averaging 2.1°C above normal in the preceding month. Parts of the eastern equatorial Pacific had anomalies above 4.0°C. These are measurements of ocean conditions, not measurements of future rainfall.

NOAA put the chance of strong-to-very-strong El Niño conditions through January–March 2027 at greater than 83%. Using its threshold for historic strength, it estimated probabilities of 54% for September–November, 83% for October–December and 70% for November–January. Those probabilities refer to the strength of the climate pattern in the stated periods; they do not assign a probability to a 2027 rainfall record.

NOAA said an event of this magnitude makes impacts consistent with El Niño more likely, while stressing that they are not guaranteed. It directs readers to seasonal outlooks for probabilities of specific impacts. That distinction is especially important for people looking for a local rainfall forecast: the agency's global El Niño assessment does not establish where, when or how much rain will fall.

Why researchers are watching 2027

UCLA lead author Chad Thackeray said, “We can't say that 2027 will break the 2024 record.” He nevertheless described conditions as aligning for another potentially exceptional year of global precipitation extremes. Senior author Alex Hall said a strong winter El Niño can prime the atmosphere for elevated extreme precipitation into the following year, while a warmer climate makes such extremes easier to reach. These are the researchers' interpretation of a possible risk, not an observed 2027 outcome.

The researchers also pointed to moisture in a warmer atmosphere and signs that Pacific warming was gathering in the eastern part of the ocean. They said eastern-Pacific El Niños correlate with rainier seasons than central-Pacific events. Their analysis used ocean-temperature measurements from December through February, when El Niño is strongest, so the developing season still matters to how closely 2027 might resemble 2024.

One important ingredient remains unresolved: Thackeray said the researchers do not yet know whether the unusual simultaneous warmth in the tropical Atlantic and Indian oceans will return in the coming season. NOAA had scheduled its next ENSO Diagnostic Discussion for November 12 and said it updates oceanic and atmospheric conditions weekly. Those observations can clarify how the El Niño develops; they cannot yet settle whether global rainfall will reach another record.