Insights from recent extreme rainfall events over Kerala: ENSO-MJO interaction

Roose, S. ORCID: https://orcid.org/0000-0002-6444-4837, Sushama, L. and Ajayamohan, R. S. (2025) Insights from recent extreme rainfall events over Kerala: ENSO-MJO interaction. Climate Dynamics, 63. 290. ISSN 1432-0894 doi: 10.1007/s00382-025-07782-w

Abstract/Summary

Kerala, situated in the southwestern tip of India, faced devastating floods during the summer monsoon seasons of 2018 and 2019, resulting in extensive property damage and claiming the lives of over 500 people. This study examines the critical role played by El Ni\~o Southern Oscillation (ENSO) and Madden--Julian Oscillation (MJO) in triggering these consecutive flood events using reanalyses and high-resolution regional climate simulation. Analysis of ERA5 reanalysis and ocean observation dataset reveals that the shallow mixed layer in the northern west Pacific Ocean during El Ni\~o years can lead to rapid intraseasonal variations in sea surface temperature in the region compared to the thicker mixed layer during La Ni\~a years, facilitating eastward advancement of convective clusters of the MJO, leading to the genesis of Low Pressure Systems (LPSs) in the Bay of Bengal and the northwest Pacific Ocean. The flood event of 2018, being an El Ni\~o year, therefore witnessed MJO propagation further east to the west Pacific Ocean. The associated extension of the monsoon jet over India led to increased vorticity to the north of its axis, supporting the formation of LPSs in the Bay of Bengal region, with enhanced precipitation over the study region, which are very well demonstrated in the high-resolution simulation. In contrast, the neutral ENSO year of 2019 experienced active MJO phases in the Indian Ocean and Maritime Continent during the monsoon season. These phases led to enhanced convection over the study region and the formation of LPSs, notably in the Bay of Bengal during the second week of August contributing to the flood event. This study underscores the intricate relationship between ENSO-MJO interactions, and their impact on monsoon dynamics and the need for improving model representation of ENSO-MJO interactions to enhance their predictability of extreme rainfall events during Indian summer monsoon.