Study finds El Nino raises chances of intense daily rain in India’s wetter regions

Climate driver ‘El Nino’, known to suppress monsoon, could however be contributing to a sharp increase in chances of extreme rainfall in a day in India’s wetter regions, according to a new study.

El Nino is the warm phase of the larger ‘El Nino-Southern Oscillation (ENSO)’ cycle, during which warmer waters of the Pacific Ocean trigger unusual patterns of rising and sinking air, thereby suppressing seasonal rainfall across the Indian subcontinent on a large-scale.

ENSO is known to alternate between El Nino, its cool counterpart ‘La Nina’ and a neutral phase—duration of one cycle can be between two and seven years.

Researchers from City College of New York and Columbia University in the US said that while light and moderate rain becomes less common during an El Nino, chances of “very heavy downpours” rise steeply in India’s wetter regions—by more than 50 per cent in some regions, potentially creating hazardous conditions.

The findings, published in the journal Science, suggest that processes which contribute to intensifying daily rainfall could be important in driving more frequent changes in rainfall patterns in the tropics under climate change.

As a result, India’s typically drier regions might see fewer rainy days and weaker showers, further compounding their dryness, researchers from City College of New York and Columbia University in the US added.

However, in the country’s wetter areas—which tend to see lesser rainfall during an El Nino—data from 1901-2020 suggests that storms tend to be “markedly more intense”, they added.

The results reveal the contrasting effects of El Nino on monsoons across India depending on the region—yet influence of ENSO and physical processes driving the effects remain largely unexplored, the researchers said.

“Although El Niño events in the equatorial Pacific are known to suppress total summer rainfall throughout India, we show using observational data spanning 1901 to 2020 that, counterintuitively, they simultaneously intensify extreme daily rainfall,” the authors wrote.

“For accumulations exceeding 250 millimetres (of rainfall), for example, statistically significant increases in likelihoods are 43 per cent for the whole domain and 59 per cent for the Central Monsoon Zone,” they said.

They added, “Extreme rainfall during the Indian summer monsoon can be destructive and deadly to the world’s third-largest economy and the most populous country.”

The authors added that the impact of El Nino on weather extremes has remained steady over time, even as it appears to have weakened on the country’s average rainfall in recent decades.

“El Nino could plausibly drive similar changes in other tropical regions, and our framework could be further applied to changes in hourly extremes,” they said. PTI