Seasonal extreme rainfall over Indian monsoon region: a moisture budget analysis to distinguish the role of ENSO and non-ENSO forcing

Indian summer monsoon rainfall (ISMR) variability of ± 10% of its long-term mean leads to flood and drought, affecting the life and economic situation of the country. It is already established that the interannual variability of ISMR is influenced by large-scale boundary forcing such as SST anomalies of tropical Pacific, Indian, and Atlantic Oceans. The ISMR association between Pacific SST anomalies in the form of El Niño Southern Oscillation (ENSO) is only studied in detail. Meanwhile, the present and previous studies show that the ENSO accounts for around 50% of the extreme years, while the other half is associated with other processes such as Atlantic Nino. A differentiation between extremes induced by ENSO and non-ENSO processes is attempted here with the help of moisture and moist static energy budget. The significant contribution to the rainfall extremes comes from moisture advection induced by anomalous winds generated by the boundary forcing and the second contribution from moisture convergence. For the non-ENSO cases, there is a contribution from local fluxes, which are not prominent in the cases of ENSO induced cases. In the ENSO cases, anomalous winds are from the equatorial central Pacific, while EQWIN/IOD cases influence extremes through the local evaporation and moisture advection from the Indian Ocean. Extreme years independent of ENSO/IOD/EQWIN have moisture advection from the anomalous winds across Africa and the Atlantic and are associated with moisture advection toward the northern parts of India. These differences in moisture processes can be responsible for the difference in rainfall distribution over India.