Arabian Sea warm pool fuelled storm cluster behind Wayanad landslide: Study

Kochi: Nearly two years after the Chooralmala-Mundakkai landslide devastated Wayanad, a new study published in Scientific Reports has linked the July 30, 2024, disaster — which left 298 dead and caused extensive destruction — to an unusual chain of atmospheric events that began over the Arabian Sea days before it struck.Researchers have found that a massive cluster of thunderstorms, known as a Mesoscale Convective Complex (MCC), fuelled by an abnormal "mini warm pool" (a localised high-temperature patch of water) over the southeastern Arabian Sea, was the primary driver of the extreme rainfall over Wayanad on July 29–30, 2024, eventually triggering the landslides. Using data from the INSAT-3DS geostationary satellite of the Indian Space Research Organisation (Isro), along with other satellite and model datasets, the team tracked the system and unravelled its evolution.The study was conducted by a team led by Dr Subin Jose of the department of physics at Newman College, Thodupuzha, and Dr Jayachandran V of the Clouds and Convective Systems Group at the National Atmospheric Research Laboratory in Tirupati."We identified the MCC as the primary driver behind the extreme rainfall recorded on July 29 and 30 in Wayanad. Our analysis shows that unusual sea surface temperature (SST) patterns played a key role in its formation, something that is relatively uncommon during the monsoon season. SST levels typically touch 30°C in the pre-monsoon season and are expected to drop to 25–27°C once monsoon rains set in. However, we found a persistent warming of about 1°C or more above normal over the southeastern Arabian Sea in SST beginning as early as July 21, and it continued until the event. This unusual warming of the sea surface intensified evaporation rates, leading to a surge in atmospheric moisture. The heightened moisture created favourable conditions for the formation of an MCC, a large storm system known to produce intense rainfall over localised regions," Jose said.The study also highlights that the event was not driven by a single factor. Instead, a combination of high moisture in the air, strong near-surface winds, and upper-level divergence helped storms to develop and persist. At the same time, conditions favoured rapid cloud growth, leading to prolonged and intense rainfall over the steep terrain of the Western Ghats, ultimately triggering the landslides.The authors warn that unusually high SSTs over the Arabian Sea, even during the monsoon season, are alarming. Such conditions could increase the frequency and intensity of extreme rainfall events over Kerala and Western Ghats in the future, posing serious risks to vulnerable regions. In a warming climate, a 1°C rise in temperature increases the atmosphere's water vapour holding capacity by approximately 7%, which can lead to more frequent extreme rainfall events and flash floods.