Multi-decadal evolution of ocean–monsoon teleconnections and the resurgence of ENSO influence on Indian summer monsoon rainfall

Understanding the variability of the Indian Summer Monsoon Rainfall (ISMR) is crucial for anticipating regional climate impacts. This study demonstrates the ISMR’s strong large-scale oceanic teleconnections, particularly with the El Niño-Southern Oscillation (ENSO) whose influence was relatively weak in earlier decades but has intensified in the current decade. By applying sliding correlations between the ISMR index and gridded ocean temperatures over 11-year windows, the study identifies dominant recurrent teleconnection patterns. A machine learning technique is then used to isolate statistically significant robust modes of variability. These patterns connect with ISMR with the phases of active and inactive periods over time. The analysis reveals new and confirms known teleconnections. Notably, revealing signals from the southern/eastern Indian Ocean and the equatorial/northern Atlantic primarily affect southern and western India, highlighting regional variations in monsoon response. Also, the influence of the tropical Pacific, both at the surface and subsurface levels, appears to be resurging, contrary to earlier studies that suggested it was weakening. These findings provide new insights and stress the need to keep monitoring large-scale oceanic influences to improve seasonal forecasts and climate risk assessments in South Asia.