Robust increase in Indian summer monsoon intraseasonal variability in the warmer climate

Despite its significant societal and scientific importance, projected changes in the characteristics of Intraseasonal Oscillations (ISOs) associated with Indian summer monsoon rainfall (ISMR) under increased greenhouse gas concentrations remain largely unexplored. This study utilizes downscaled and bias-corrected historical simulations and projections from 17 models of the Coupled Model Intercomparison Project Phase 6 (CMIP6) to investigate the future evolution of ISOs. Our findings reveal a twofold increase in ISO variability over India in the far future under the very high emissions scenario, raising critical concerns about its adverse socioeconomic impacts. Our analysis suggests that the increased magnitude of precipitation anomalies associated with northward propagating ISOs may intensify active monsoon spells, potentially triggering extreme rainfall events. Additionally, the phase speed of these northward-propagating ISOs over the Bay of Bengal is projected to accelerate due to weakened air-sea coupling and feedback. This acceleration reduces the northwest-southeast tilt of the precipitation band, altering the spatial structure of the ISOs. Concurrently, the strengthening of circulation-precipitation feedback and warming of the Indian Ocean are projected to enhance the phase speed of monsoon ISOs, leading to more frequent active spells. This study underscores the critical role of regional ocean-atmosphere feedback in shaping future ISO characteristics, highlighting the urgent need for improved understanding and prediction of these changes in the context of a warming climate.