More extreme Indian monsoon rainfall in El Niño summers.

Extreme rainfall during the Indian summer monsoon can be destructive and deadly to the world's third-largest economy and most populous country. 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. This is partly driven by increases in extreme daily values of convective buoyancy, provided that both the undilute instability of near-surface air and the dilution by mixing with drier air above are considered. El Niño could plausibly drive similar changes in other tropical regions, and our framework could be further applied to changes in hourly extremes, to other internal variability modes, and to forced trends under climate change. Editor's summary: India, the world's most populous country and third-largest economy, depends on the rainfall it receives during the summer monsoon season. How much and when that rain falls has major implications for the environment, agriculture, water supply, and river flow. Hill et al. found that although the well-documented effect of El Niño events is to decrease summer rainfall, it also paradoxically intensifies extreme daily precipitation amounts, thereby resulting in hazardous conditions across the region. The processes that create this intensification may be important in other tropical locations as well. —Jesse Smith [ABSTRACT FROM AUTHOR]