Although El Niño suppresses overall monsoon season rainfall across India, a new study finds that it also, counterintuitively, sharply increases the likelihood of extreme daily downpours in the country’s wetter regions. The findings suggest that the processes that drive this intensification may play an important role in driving extreme rainfall variability under climate change in other tropical locations. It’s long been known that the El Niño-Southern Oscillation (ENSO) exerts a powerful influence on India’s summer monsoon rains. During El Niño years, warmer Pacific waters trigger unusual patterns of rising and sinking air, producing a large-scale suppression of seasonal rainfall across the Indian subcontinent. In India’s typically drier regions, this results in fewer rainy days and weaker showers, compounding their dryness. However, in the nation’s climatologically wetter zones, which also experience less frequent rainfall during El Niño events, observations suggest that the storms that do occur tend to be markedly more intense. This contrasting pattern underscores El Niño’s complex and regionally varied impact on India’s monsoon rains. Yet, despite this, ENSOs’ influence on the Indian summer monsoon, and the physical mechanisms driving these patterns, remain largely unexplored. To address this gap, Spencer Hill and colleagues measured extreme daily rainfall using a cutoff accumulation metric, which captures how often very heavy rain occurs relative to average conditions. Applying this to over a century of high-resolution Indian rainfall observational data (1901–2020), Hill et al. found that while light and moderate rain become less frequent during El Niño, the probability of very heavy downpours rises steeply in India’s wetter regions, with extreme rainfall events becoming more than 50% likelier in some cases, which can result in potentially hazardous conditions. Moreover, unlike El Niño’s weakening influence on India’s average summer rainfall over recent decades, its impact on extremes has remained comparatively steady over time, though with some regional shifts. According to the authors, this intensification is linked to changes in atmospheric buoyancy and low-pressure system tracks.
