Study of extreme Indian rainfall upends conventional wisdom

A new study published in the journal ScienceLed by scientists from the City College in New York (CCNY) and Columbia University, calls into question the long -standing beliefs about the way in which El Niño events influence precipitation during the Indian summer monsoon. The results show that even if El Niño often provides drought conditions to India on the whole, this also increases the probability of a devastating downpour in some of the most populous regions of the country.

“Our main observation is that you tend to obtain more days with extreme quantities of precipitation in India, no less, during the summers of El Niño”, explains the main author Spencer Hill, professor at CCNY and affiliated with the Lamont-Doherty Earth Observatory, which is part of the Columbia Climate School.

“This result has been unexpected, because we have known for more than a century that El Niño events are precisely the opposite for total precipitation added during the rainy season, from June to September.”

The research team has combined more than a century of precipitation observations with high -resolution precipitation data and advanced atmospheric diagnoses to discover this paradoxical effect of El Niño.

“A key advance in the approach of our study is that, even if it deals with rare events, it allows robust differences to emerge without grouping all data in a single bucket of Indian precipitation ” ‘, explains the co-author Michela Biasutti. “In doing so, we were able to see changes in the opposite sign in the rainiest and drier regions of the subcontinent.”

The increases in extreme daily precipitation under El Niño compared to the Niña are concentrated in the center of India and in the southwest coastal strip, says Hill. “In the south-east and the northwest, however, the signal is opposed, which means that daily extreme precipitation is less likely in the summers of El Niño.”

In India, floods and other extreme meteorological events have generalized and serious impacts each year. In 2024, they killed more than 3,000 people, destroyed or damaged 230,000 houses and buildings and killed nearly 10,000 cattle heads.

The results of the study also indicate opportunities for improving seasonal forecasts. A preliminary warning could help civil servants better prepare for disasters by issuing flood alerts earlier, by prepressing emergency supplies or by strengthening vulnerable infrastructure.

“Our results open the door to the creation of seasonal perspectives for extreme events in India, on the basis of the slowly evolving temperature of the ocean,” explains Biasutti. “This study focused on the discovery of the effects of the ENSO, but the same physical mechanisms could apply to other natural variability modes. They could also be relevant to understand anthropogenic changes in extreme precipitation.”

ENSO, which means El Niño-Southern Oscillation, is the favorite name of scientists for the climate phenomenon which encompasses the El Niño and Niña phases.

In the 1980s, Mark Cane de Lamont, who was also the author of this study, co-developed the first world model of El Niño, laying the basics of the seasonal forecast of today’s climate.

Hill says that the team’s work will continue, thanks to a new three -year subsidy from the National Science Foundation.

“We will study how and why the type of storms responsible for a large part of this extreme precipitation, called low pressure systems of the monsoon, change depending on whether there are El Niño or Niña conditions,” he said.

In addition to CCNY and LDEO researchers, the study team included scientists from the applied physics department of Columbia and applied mathematics and the University of California in Los Angeles.

This story is republished with the kind authorization of Earth Institute, Columbia University http://blogs.ei.columbia.edu.