Unravelling the link between extreme rainfall and tropical wave activity over the west coast of India

This study examines the influence of convectively coupled equatorial waves (CCEWs) on extreme rainfall over the west coast of India across all seasons. The results show that CCEWs substantially amplify extreme rainfall, with Rossby waves exerting the strongest impact, followed by Mixed Rossby-Gravity (MRG) and Kevin waves. Overall, these waves enhance land rainfall extremes by about 20-60 %, while amplification over adjacent oceanic regions can exceed 150 %. Wave activity associated with Kelvin and Rossby waves remains relatively uniform throughout the year, whereas MRG waves exhibit pronounced seasonality, peaking during June-September. During summer, the enhancement in extreme rainfall linked to MRG waves is comparable to that of Rossby waves, while in winter the influence of all wave types is largely confined to the southernmost part of India. The amplification of rainfall primarily arises from wave-induced increases in moisture convergence and the subsequent development of deep convective systems, further supported by strong interactions between the dynamical waves and the orography of the Western Ghats. The waves are not only instrumental in magnifying extreme rainfall but also in increasing its probability, with Rossby and MRG waves playing a major role in this process, while Kelvin wave's effect is insignificant. The study observes that the devastating extreme rainfall events over the southwest coast in 2018, 2019, and 2024 are linked to strong wave activity. These findings provide new insight into the mechanisms that intensify rainfall extremes over the west coast of India and highlight the potential for improving extreme rainfall forecasts using the predictable nature of equatorial wave activity.