Future projections of heat extreme modulation by subseasonal oscillations over India as simulated by the CMIP6 models

This study evaluates the ability of 15 CMIP6 models to capture Tropical Subseasonal Oscillations (TSOs) and their influence on the heat extremes over the Indian region along with their future projections. Based on the individual model’s capability to simulate the intensity, wavenumber-frequency spectrum, and propagation characteristics of various TSOs, an ensemble of the five best-performing models for each TSO is selected and their future projections of heat extremes are assessed. The model historical ensembles agree well with the observed heat extremes modulation by TSOs. Future projections under SSP126, SSP245, and SSP585 scenarios reveal that the dry phases of TSOs enhance the heat extreme frequency across India, with their influence becoming more pronounced under higher emission scenarios. The Equatorial Rossby (ER) wave has the strongest influence on heat extreme frequency and intensity in the future scenarios, and Boreal Summer Intraseasonal Oscillation (BSISO) mainly increases the heat extreme frequency, with minimal impact on the intensity of heat extremes. The Kelvin and MT (Mixed Rossby Gravity wave and Tropical Depression) waves mostly increase the heat extreme frequency over the southern Indian region. This is attributed to enhanced TSO activity as we go from lower to higher emission scenarios. Overall, the results suggest that in a warming climate, the TSOs will significantly amplify the frequency, however, the intensity of heat extremes over India depends on the warming scenarios, with severe scenarios showing less modulation by TSOs. This work highlights the importance of accounting for intraseasonal variability in future heat extreme projections, offering valuable insights for climate risk assessment and early warning system development.